blk-core.c 73.5 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543 2544 2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607 2608 2609 2610 2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796 2797
/*
 * Copyright (C) 1991, 1992 Linus Torvalds
 * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
 * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
 * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
 * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au>
 *	-  July2000
 * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
 */

/*
 * This handles all read/write requests to block devices
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/fault-inject.h>
#include <linux/list_sort.h>

#define CREATE_TRACE_POINTS
#include <trace/events/block.h>

#include "blk.h"

EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);

static int __make_request(struct request_queue *q, struct bio *bio);

/*
 * For the allocated request tables
 */
static struct kmem_cache *request_cachep;

/*
 * For queue allocation
 */
struct kmem_cache *blk_requestq_cachep;

/*
 * Controlling structure to kblockd
 */
static struct workqueue_struct *kblockd_workqueue;

static void drive_stat_acct(struct request *rq, int new_io)
{
	struct hd_struct *part;
	int rw = rq_data_dir(rq);
	int cpu;

	if (!blk_do_io_stat(rq))
		return;

	cpu = part_stat_lock();

	if (!new_io) {
		part = rq->part;
		part_stat_inc(cpu, part, merges[rw]);
	} else {
		part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
		if (!hd_struct_try_get(part)) {
			/*
			 * The partition is already being removed,
			 * the request will be accounted on the disk only
			 *
			 * We take a reference on disk->part0 although that
			 * partition will never be deleted, so we can treat
			 * it as any other partition.
			 */
			part = &rq->rq_disk->part0;
			hd_struct_get(part);
		}
		part_round_stats(cpu, part);
		part_inc_in_flight(part, rw);
		rq->part = part;
	}

	part_stat_unlock();
}

void blk_queue_congestion_threshold(struct request_queue *q)
{
	int nr;

	nr = q->nr_requests - (q->nr_requests / 8) + 1;
	if (nr > q->nr_requests)
		nr = q->nr_requests;
	q->nr_congestion_on = nr;

	nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
	if (nr < 1)
		nr = 1;
	q->nr_congestion_off = nr;
}

/**
 * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
 * @bdev:	device
 *
 * Locates the passed device's request queue and returns the address of its
 * backing_dev_info
 *
 * Will return NULL if the request queue cannot be located.
 */
struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
{
	struct backing_dev_info *ret = NULL;
	struct request_queue *q = bdev_get_queue(bdev);

	if (q)
		ret = &q->backing_dev_info;
	return ret;
}
EXPORT_SYMBOL(blk_get_backing_dev_info);

void blk_rq_init(struct request_queue *q, struct request *rq)
{
	memset(rq, 0, sizeof(*rq));

	INIT_LIST_HEAD(&rq->queuelist);
	INIT_LIST_HEAD(&rq->timeout_list);
	rq->cpu = -1;
	rq->q = q;
	rq->__sector = (sector_t) -1;
	INIT_HLIST_NODE(&rq->hash);
	RB_CLEAR_NODE(&rq->rb_node);
	rq->cmd = rq->__cmd;
	rq->cmd_len = BLK_MAX_CDB;
	rq->tag = -1;
	rq->ref_count = 1;
	rq->start_time = jiffies;
	set_start_time_ns(rq);
	rq->part = NULL;
}
EXPORT_SYMBOL(blk_rq_init);

static void req_bio_endio(struct request *rq, struct bio *bio,
			  unsigned int nbytes, int error)
{
	if (error)
		clear_bit(BIO_UPTODATE, &bio->bi_flags);
	else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
		error = -EIO;

	if (unlikely(nbytes > bio->bi_size)) {
		printk(KERN_ERR "%s: want %u bytes done, %u left\n",
		       __func__, nbytes, bio->bi_size);
		nbytes = bio->bi_size;
	}

	if (unlikely(rq->cmd_flags & REQ_QUIET))
		set_bit(BIO_QUIET, &bio->bi_flags);

	bio->bi_size -= nbytes;
	bio->bi_sector += (nbytes >> 9);

	if (bio_integrity(bio))
		bio_integrity_advance(bio, nbytes);

	/* don't actually finish bio if it's part of flush sequence */
	if (bio->bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))
		bio_endio(bio, error);
}

void blk_dump_rq_flags(struct request *rq, char *msg)
{
	int bit;

	printk(KERN_INFO "%s: dev %s: type=%x, flags=%x\n", msg,
		rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->cmd_type,
		rq->cmd_flags);

	printk(KERN_INFO "  sector %llu, nr/cnr %u/%u\n",
	       (unsigned long long)blk_rq_pos(rq),
	       blk_rq_sectors(rq), blk_rq_cur_sectors(rq));
	printk(KERN_INFO "  bio %p, biotail %p, buffer %p, len %u\n",
	       rq->bio, rq->biotail, rq->buffer, blk_rq_bytes(rq));

	if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
		printk(KERN_INFO "  cdb: ");
		for (bit = 0; bit < BLK_MAX_CDB; bit++)
			printk("%02x ", rq->cmd[bit]);
		printk("\n");
	}
}
EXPORT_SYMBOL(blk_dump_rq_flags);

static void blk_delay_work(struct work_struct *work)
{
	struct request_queue *q;

	q = container_of(work, struct request_queue, delay_work.work);
	spin_lock_irq(q->queue_lock);
	__blk_run_queue(q);
	spin_unlock_irq(q->queue_lock);
}

/**
 * blk_delay_queue - restart queueing after defined interval
 * @q:		The &struct request_queue in question
 * @msecs:	Delay in msecs
 *
 * Description:
 *   Sometimes queueing needs to be postponed for a little while, to allow
 *   resources to come back. This function will make sure that queueing is
 *   restarted around the specified time.
 */
void blk_delay_queue(struct request_queue *q, unsigned long msecs)
{
	queue_delayed_work(kblockd_workqueue, &q->delay_work,
				msecs_to_jiffies(msecs));
}
EXPORT_SYMBOL(blk_delay_queue);

/**
 * blk_start_queue - restart a previously stopped queue
 * @q:    The &struct request_queue in question
 *
 * Description:
 *   blk_start_queue() will clear the stop flag on the queue, and call
 *   the request_fn for the queue if it was in a stopped state when
 *   entered. Also see blk_stop_queue(). Queue lock must be held.
 **/
void blk_start_queue(struct request_queue *q)
{
	WARN_ON(!irqs_disabled());

	queue_flag_clear(QUEUE_FLAG_STOPPED, q);
	__blk_run_queue(q);
}
EXPORT_SYMBOL(blk_start_queue);

/**
 * blk_stop_queue - stop a queue
 * @q:    The &struct request_queue in question
 *
 * Description:
 *   The Linux block layer assumes that a block driver will consume all
 *   entries on the request queue when the request_fn strategy is called.
 *   Often this will not happen, because of hardware limitations (queue
 *   depth settings). If a device driver gets a 'queue full' response,
 *   or if it simply chooses not to queue more I/O at one point, it can
 *   call this function to prevent the request_fn from being called until
 *   the driver has signalled it's ready to go again. This happens by calling
 *   blk_start_queue() to restart queue operations. Queue lock must be held.
 **/
void blk_stop_queue(struct request_queue *q)
{
	__cancel_delayed_work(&q->delay_work);
	queue_flag_set(QUEUE_FLAG_STOPPED, q);
}
EXPORT_SYMBOL(blk_stop_queue);

/**
 * blk_sync_queue - cancel any pending callbacks on a queue
 * @q: the queue
 *
 * Description:
 *     The block layer may perform asynchronous callback activity
 *     on a queue, such as calling the unplug function after a timeout.
 *     A block device may call blk_sync_queue to ensure that any
 *     such activity is cancelled, thus allowing it to release resources
 *     that the callbacks might use. The caller must already have made sure
 *     that its ->make_request_fn will not re-add plugging prior to calling
 *     this function.
 *
 *     This function does not cancel any asynchronous activity arising
 *     out of elevator or throttling code. That would require elevaotor_exit()
 *     and blk_throtl_exit() to be called with queue lock initialized.
 *
 */
void blk_sync_queue(struct request_queue *q)
{
	del_timer_sync(&q->timeout);
	cancel_delayed_work_sync(&q->delay_work);
}
EXPORT_SYMBOL(blk_sync_queue);

/**
 * __blk_run_queue - run a single device queue
 * @q:	The queue to run
 *
 * Description:
 *    See @blk_run_queue. This variant must be called with the queue lock
 *    held and interrupts disabled.
 */
void __blk_run_queue(struct request_queue *q)
{
	if (unlikely(blk_queue_stopped(q)))
		return;

	q->request_fn(q);
}
EXPORT_SYMBOL(__blk_run_queue);

/**
 * blk_run_queue_async - run a single device queue in workqueue context
 * @q:	The queue to run
 *
 * Description:
 *    Tells kblockd to perform the equivalent of @blk_run_queue on behalf
 *    of us.
 */
void blk_run_queue_async(struct request_queue *q)
{
	if (likely(!blk_queue_stopped(q))) {
		__cancel_delayed_work(&q->delay_work);
		queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
	}
}
EXPORT_SYMBOL(blk_run_queue_async);

/**
 * blk_run_queue - run a single device queue
 * @q: The queue to run
 *
 * Description:
 *    Invoke request handling on this queue, if it has pending work to do.
 *    May be used to restart queueing when a request has completed.
 */
void blk_run_queue(struct request_queue *q)
{
	unsigned long flags;

	spin_lock_irqsave(q->queue_lock, flags);
	__blk_run_queue(q);
	spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(blk_run_queue);

void blk_put_queue(struct request_queue *q)
{
	kobject_put(&q->kobj);
}
EXPORT_SYMBOL(blk_put_queue);

/*
 * Note: If a driver supplied the queue lock, it should not zap that lock
 * unexpectedly as some queue cleanup components like elevator_exit() and
 * blk_throtl_exit() need queue lock.
 */
void blk_cleanup_queue(struct request_queue *q)
{
	/*
	 * We know we have process context here, so we can be a little
	 * cautious and ensure that pending block actions on this device
	 * are done before moving on. Going into this function, we should
	 * not have processes doing IO to this device.
	 */
	blk_sync_queue(q);

	del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
	mutex_lock(&q->sysfs_lock);
	queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
	mutex_unlock(&q->sysfs_lock);

	if (q->elevator)
		elevator_exit(q->elevator);

	blk_throtl_exit(q);

	blk_put_queue(q);
}
EXPORT_SYMBOL(blk_cleanup_queue);

static int blk_init_free_list(struct request_queue *q)
{
	struct request_list *rl = &q->rq;

	if (unlikely(rl->rq_pool))
		return 0;

	rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
	rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;
	rl->elvpriv = 0;
	init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
	init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);

	rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
				mempool_free_slab, request_cachep, q->node);

	if (!rl->rq_pool)
		return -ENOMEM;

	return 0;
}

struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
{
	return blk_alloc_queue_node(gfp_mask, -1);
}
EXPORT_SYMBOL(blk_alloc_queue);

struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
{
	struct request_queue *q;
	int err;

	q = kmem_cache_alloc_node(blk_requestq_cachep,
				gfp_mask | __GFP_ZERO, node_id);
	if (!q)
		return NULL;

	q->backing_dev_info.ra_pages =
			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
	q->backing_dev_info.state = 0;
	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
	q->backing_dev_info.name = "block";

	err = bdi_init(&q->backing_dev_info);
	if (err) {
		kmem_cache_free(blk_requestq_cachep, q);
		return NULL;
	}

	if (blk_throtl_init(q)) {
		kmem_cache_free(blk_requestq_cachep, q);
		return NULL;
	}

	setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
		    laptop_mode_timer_fn, (unsigned long) q);
	setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
	INIT_LIST_HEAD(&q->timeout_list);
	INIT_LIST_HEAD(&q->flush_queue[0]);
	INIT_LIST_HEAD(&q->flush_queue[1]);
	INIT_LIST_HEAD(&q->flush_data_in_flight);
	INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);

	kobject_init(&q->kobj, &blk_queue_ktype);

	mutex_init(&q->sysfs_lock);
	spin_lock_init(&q->__queue_lock);

	/*
	 * By default initialize queue_lock to internal lock and driver can
	 * override it later if need be.
	 */
	q->queue_lock = &q->__queue_lock;

	return q;
}
EXPORT_SYMBOL(blk_alloc_queue_node);

/**
 * blk_init_queue  - prepare a request queue for use with a block device
 * @rfn:  The function to be called to process requests that have been
 *        placed on the queue.
 * @lock: Request queue spin lock
 *
 * Description:
 *    If a block device wishes to use the standard request handling procedures,
 *    which sorts requests and coalesces adjacent requests, then it must
 *    call blk_init_queue().  The function @rfn will be called when there
 *    are requests on the queue that need to be processed.  If the device
 *    supports plugging, then @rfn may not be called immediately when requests
 *    are available on the queue, but may be called at some time later instead.
 *    Plugged queues are generally unplugged when a buffer belonging to one
 *    of the requests on the queue is needed, or due to memory pressure.
 *
 *    @rfn is not required, or even expected, to remove all requests off the
 *    queue, but only as many as it can handle at a time.  If it does leave
 *    requests on the queue, it is responsible for arranging that the requests
 *    get dealt with eventually.
 *
 *    The queue spin lock must be held while manipulating the requests on the
 *    request queue; this lock will be taken also from interrupt context, so irq
 *    disabling is needed for it.
 *
 *    Function returns a pointer to the initialized request queue, or %NULL if
 *    it didn't succeed.
 *
 * Note:
 *    blk_init_queue() must be paired with a blk_cleanup_queue() call
 *    when the block device is deactivated (such as at module unload).
 **/

struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
{
	return blk_init_queue_node(rfn, lock, -1);
}
EXPORT_SYMBOL(blk_init_queue);

struct request_queue *
blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
{
	struct request_queue *uninit_q, *q;

	uninit_q = blk_alloc_queue_node(GFP_KERNEL, node_id);
	if (!uninit_q)
		return NULL;

	q = blk_init_allocated_queue_node(uninit_q, rfn, lock, node_id);
	if (!q)
		blk_cleanup_queue(uninit_q);

	return q;
}
EXPORT_SYMBOL(blk_init_queue_node);

struct request_queue *
blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
			 spinlock_t *lock)
{
	return blk_init_allocated_queue_node(q, rfn, lock, -1);
}
EXPORT_SYMBOL(blk_init_allocated_queue);

struct request_queue *
blk_init_allocated_queue_node(struct request_queue *q, request_fn_proc *rfn,
			      spinlock_t *lock, int node_id)
{
	if (!q)
		return NULL;

	q->node = node_id;
	if (blk_init_free_list(q))
		return NULL;

	q->request_fn		= rfn;
	q->prep_rq_fn		= NULL;
	q->unprep_rq_fn		= NULL;
	q->queue_flags		= QUEUE_FLAG_DEFAULT;

	/* Override internal queue lock with supplied lock pointer */
	if (lock)
		q->queue_lock		= lock;

	/*
	 * This also sets hw/phys segments, boundary and size
	 */
	blk_queue_make_request(q, __make_request);

	q->sg_reserved_size = INT_MAX;

	/*
	 * all done
	 */
	if (!elevator_init(q, NULL)) {
		blk_queue_congestion_threshold(q);
		return q;
	}

	return NULL;
}
EXPORT_SYMBOL(blk_init_allocated_queue_node);

int blk_get_queue(struct request_queue *q)
{
	if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
		kobject_get(&q->kobj);
		return 0;
	}

	return 1;
}
EXPORT_SYMBOL(blk_get_queue);

static inline void blk_free_request(struct request_queue *q, struct request *rq)
{
	if (rq->cmd_flags & REQ_ELVPRIV)
		elv_put_request(q, rq);
	mempool_free(rq, q->rq.rq_pool);
}

static struct request *
blk_alloc_request(struct request_queue *q, int flags, int priv, gfp_t gfp_mask)
{
	struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);

	if (!rq)
		return NULL;

	blk_rq_init(q, rq);

	rq->cmd_flags = flags | REQ_ALLOCED;

	if (priv) {
		if (unlikely(elv_set_request(q, rq, gfp_mask))) {
			mempool_free(rq, q->rq.rq_pool);
			return NULL;
		}
		rq->cmd_flags |= REQ_ELVPRIV;
	}

	return rq;
}

/*
 * ioc_batching returns true if the ioc is a valid batching request and
 * should be given priority access to a request.
 */
static inline int ioc_batching(struct request_queue *q, struct io_context *ioc)
{
	if (!ioc)
		return 0;

	/*
	 * Make sure the process is able to allocate at least 1 request
	 * even if the batch times out, otherwise we could theoretically
	 * lose wakeups.
	 */
	return ioc->nr_batch_requests == q->nr_batching ||
		(ioc->nr_batch_requests > 0
		&& time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
}

/*
 * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
 * will cause the process to be a "batcher" on all queues in the system. This
 * is the behaviour we want though - once it gets a wakeup it should be given
 * a nice run.
 */
static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
{
	if (!ioc || ioc_batching(q, ioc))
		return;

	ioc->nr_batch_requests = q->nr_batching;
	ioc->last_waited = jiffies;
}

static void __freed_request(struct request_queue *q, int sync)
{
	struct request_list *rl = &q->rq;

	if (rl->count[sync] < queue_congestion_off_threshold(q))
		blk_clear_queue_congested(q, sync);

	if (rl->count[sync] + 1 <= q->nr_requests) {
		if (waitqueue_active(&rl->wait[sync]))
			wake_up(&rl->wait[sync]);

		blk_clear_queue_full(q, sync);
	}
}

/*
 * A request has just been released.  Account for it, update the full and
 * congestion status, wake up any waiters.   Called under q->queue_lock.
 */
static void freed_request(struct request_queue *q, int sync, int priv)
{
	struct request_list *rl = &q->rq;

	rl->count[sync]--;
	if (priv)
		rl->elvpriv--;

	__freed_request(q, sync);

	if (unlikely(rl->starved[sync ^ 1]))
		__freed_request(q, sync ^ 1);
}

/*
 * Determine if elevator data should be initialized when allocating the
 * request associated with @bio.
 */
static bool blk_rq_should_init_elevator(struct bio *bio)
{
	if (!bio)
		return true;

	/*
	 * Flush requests do not use the elevator so skip initialization.
	 * This allows a request to share the flush and elevator data.
	 */
	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA))
		return false;

	return true;
}

/*
 * Get a free request, queue_lock must be held.
 * Returns NULL on failure, with queue_lock held.
 * Returns !NULL on success, with queue_lock *not held*.
 */
static struct request *get_request(struct request_queue *q, int rw_flags,
				   struct bio *bio, gfp_t gfp_mask)
{
	struct request *rq = NULL;
	struct request_list *rl = &q->rq;
	struct io_context *ioc = NULL;
	const bool is_sync = rw_is_sync(rw_flags) != 0;
	int may_queue, priv = 0;

	may_queue = elv_may_queue(q, rw_flags);
	if (may_queue == ELV_MQUEUE_NO)
		goto rq_starved;

	if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
		if (rl->count[is_sync]+1 >= q->nr_requests) {
			ioc = current_io_context(GFP_ATOMIC, q->node);
			/*
			 * The queue will fill after this allocation, so set
			 * it as full, and mark this process as "batching".
			 * This process will be allowed to complete a batch of
			 * requests, others will be blocked.
			 */
			if (!blk_queue_full(q, is_sync)) {
				ioc_set_batching(q, ioc);
				blk_set_queue_full(q, is_sync);
			} else {
				if (may_queue != ELV_MQUEUE_MUST
						&& !ioc_batching(q, ioc)) {
					/*
					 * The queue is full and the allocating
					 * process is not a "batcher", and not
					 * exempted by the IO scheduler
					 */
					goto out;
				}
			}
		}
		blk_set_queue_congested(q, is_sync);
	}

	/*
	 * Only allow batching queuers to allocate up to 50% over the defined
	 * limit of requests, otherwise we could have thousands of requests
	 * allocated with any setting of ->nr_requests
	 */
	if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
		goto out;

	rl->count[is_sync]++;
	rl->starved[is_sync] = 0;

	if (blk_rq_should_init_elevator(bio)) {
		priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
		if (priv)
			rl->elvpriv++;
	}

	if (blk_queue_io_stat(q))
		rw_flags |= REQ_IO_STAT;
	spin_unlock_irq(q->queue_lock);

	rq = blk_alloc_request(q, rw_flags, priv, gfp_mask);
	if (unlikely(!rq)) {
		/*
		 * Allocation failed presumably due to memory. Undo anything
		 * we might have messed up.
		 *
		 * Allocating task should really be put onto the front of the
		 * wait queue, but this is pretty rare.
		 */
		spin_lock_irq(q->queue_lock);
		freed_request(q, is_sync, priv);

		/*
		 * in the very unlikely event that allocation failed and no
		 * requests for this direction was pending, mark us starved
		 * so that freeing of a request in the other direction will
		 * notice us. another possible fix would be to split the
		 * rq mempool into READ and WRITE
		 */
rq_starved:
		if (unlikely(rl->count[is_sync] == 0))
			rl->starved[is_sync] = 1;

		goto out;
	}

	/*
	 * ioc may be NULL here, and ioc_batching will be false. That's
	 * OK, if the queue is under the request limit then requests need
	 * not count toward the nr_batch_requests limit. There will always
	 * be some limit enforced by BLK_BATCH_TIME.
	 */
	if (ioc_batching(q, ioc))
		ioc->nr_batch_requests--;

	trace_block_getrq(q, bio, rw_flags & 1);
out:
	return rq;
}

/*
 * No available requests for this queue, wait for some requests to become
 * available.
 *
 * Called with q->queue_lock held, and returns with it unlocked.
 */
static struct request *get_request_wait(struct request_queue *q, int rw_flags,
					struct bio *bio)
{
	const bool is_sync = rw_is_sync(rw_flags) != 0;
	struct request *rq;

	rq = get_request(q, rw_flags, bio, GFP_NOIO);
	while (!rq) {
		DEFINE_WAIT(wait);
		struct io_context *ioc;
		struct request_list *rl = &q->rq;

		prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
				TASK_UNINTERRUPTIBLE);

		trace_block_sleeprq(q, bio, rw_flags & 1);

		spin_unlock_irq(q->queue_lock);
		io_schedule();

		/*
		 * After sleeping, we become a "batching" process and
		 * will be able to allocate at least one request, and
		 * up to a big batch of them for a small period time.
		 * See ioc_batching, ioc_set_batching
		 */
		ioc = current_io_context(GFP_NOIO, q->node);
		ioc_set_batching(q, ioc);

		spin_lock_irq(q->queue_lock);
		finish_wait(&rl->wait[is_sync], &wait);

		rq = get_request(q, rw_flags, bio, GFP_NOIO);
	};

	return rq;
}

struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
{
	struct request *rq;

	if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
		return NULL;

	BUG_ON(rw != READ && rw != WRITE);

	spin_lock_irq(q->queue_lock);
	if (gfp_mask & __GFP_WAIT) {
		rq = get_request_wait(q, rw, NULL);
	} else {
		rq = get_request(q, rw, NULL, gfp_mask);
		if (!rq)
			spin_unlock_irq(q->queue_lock);
	}
	/* q->queue_lock is unlocked at this point */

	return rq;
}
EXPORT_SYMBOL(blk_get_request);

/**
 * blk_make_request - given a bio, allocate a corresponding struct request.
 * @q: target request queue
 * @bio:  The bio describing the memory mappings that will be submitted for IO.
 *        It may be a chained-bio properly constructed by block/bio layer.
 * @gfp_mask: gfp flags to be used for memory allocation
 *
 * blk_make_request is the parallel of generic_make_request for BLOCK_PC
 * type commands. Where the struct request needs to be farther initialized by
 * the caller. It is passed a &struct bio, which describes the memory info of
 * the I/O transfer.
 *
 * The caller of blk_make_request must make sure that bi_io_vec
 * are set to describe the memory buffers. That bio_data_dir() will return
 * the needed direction of the request. (And all bio's in the passed bio-chain
 * are properly set accordingly)
 *
 * If called under none-sleepable conditions, mapped bio buffers must not
 * need bouncing, by calling the appropriate masked or flagged allocator,
 * suitable for the target device. Otherwise the call to blk_queue_bounce will
 * BUG.
 *
 * WARNING: When allocating/cloning a bio-chain, careful consideration should be
 * given to how you allocate bios. In particular, you cannot use __GFP_WAIT for
 * anything but the first bio in the chain. Otherwise you risk waiting for IO
 * completion of a bio that hasn't been submitted yet, thus resulting in a
 * deadlock. Alternatively bios should be allocated using bio_kmalloc() instead
 * of bio_alloc(), as that avoids the mempool deadlock.
 * If possible a big IO should be split into smaller parts when allocation
 * fails. Partial allocation should not be an error, or you risk a live-lock.
 */
struct request *blk_make_request(struct request_queue *q, struct bio *bio,
				 gfp_t gfp_mask)
{
	struct request *rq = blk_get_request(q, bio_data_dir(bio), gfp_mask);

	if (unlikely(!rq))
		return ERR_PTR(-ENOMEM);

	for_each_bio(bio) {
		struct bio *bounce_bio = bio;
		int ret;

		blk_queue_bounce(q, &bounce_bio);
		ret = blk_rq_append_bio(q, rq, bounce_bio);
		if (unlikely(ret)) {
			blk_put_request(rq);
			return ERR_PTR(ret);
		}
	}

	return rq;
}
EXPORT_SYMBOL(blk_make_request);

/**
 * blk_requeue_request - put a request back on queue
 * @q:		request queue where request should be inserted
 * @rq:		request to be inserted
 *
 * Description:
 *    Drivers often keep queueing requests until the hardware cannot accept
 *    more, when that condition happens we need to put the request back
 *    on the queue. Must be called with queue lock held.
 */
void blk_requeue_request(struct request_queue *q, struct request *rq)
{
	blk_delete_timer(rq);
	blk_clear_rq_complete(rq);
	trace_block_rq_requeue(q, rq);

	if (blk_rq_tagged(rq))
		blk_queue_end_tag(q, rq);

	BUG_ON(blk_queued_rq(rq));

	elv_requeue_request(q, rq);
}
EXPORT_SYMBOL(blk_requeue_request);

static void add_acct_request(struct request_queue *q, struct request *rq,
			     int where)
{
	drive_stat_acct(rq, 1);
	__elv_add_request(q, rq, where);
}

/**
 * blk_insert_request - insert a special request into a request queue
 * @q:		request queue where request should be inserted
 * @rq:		request to be inserted
 * @at_head:	insert request at head or tail of queue
 * @data:	private data
 *
 * Description:
 *    Many block devices need to execute commands asynchronously, so they don't
 *    block the whole kernel from preemption during request execution.  This is
 *    accomplished normally by inserting aritficial requests tagged as
 *    REQ_TYPE_SPECIAL in to the corresponding request queue, and letting them
 *    be scheduled for actual execution by the request queue.
 *
 *    We have the option of inserting the head or the tail of the queue.
 *    Typically we use the tail for new ioctls and so forth.  We use the head
 *    of the queue for things like a QUEUE_FULL message from a device, or a
 *    host that is unable to accept a particular command.
 */
void blk_insert_request(struct request_queue *q, struct request *rq,
			int at_head, void *data)
{
	int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
	unsigned long flags;

	/*
	 * tell I/O scheduler that this isn't a regular read/write (ie it
	 * must not attempt merges on this) and that it acts as a soft
	 * barrier
	 */
	rq->cmd_type = REQ_TYPE_SPECIAL;

	rq->special = data;

	spin_lock_irqsave(q->queue_lock, flags);

	/*
	 * If command is tagged, release the tag
	 */
	if (blk_rq_tagged(rq))
		blk_queue_end_tag(q, rq);

	add_acct_request(q, rq, where);
	__blk_run_queue(q);
	spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(blk_insert_request);

static void part_round_stats_single(int cpu, struct hd_struct *part,
				    unsigned long now)
{
	if (now == part->stamp)
		return;

	if (part_in_flight(part)) {
		__part_stat_add(cpu, part, time_in_queue,
				part_in_flight(part) * (now - part->stamp));
		__part_stat_add(cpu, part, io_ticks, (now - part->stamp));
	}
	part->stamp = now;
}

/**
 * part_round_stats() - Round off the performance stats on a struct disk_stats.
 * @cpu: cpu number for stats access
 * @part: target partition
 *
 * The average IO queue length and utilisation statistics are maintained
 * by observing the current state of the queue length and the amount of
 * time it has been in this state for.
 *
 * Normally, that accounting is done on IO completion, but that can result
 * in more than a second's worth of IO being accounted for within any one
 * second, leading to >100% utilisation.  To deal with that, we call this
 * function to do a round-off before returning the results when reading
 * /proc/diskstats.  This accounts immediately for all queue usage up to
 * the current jiffies and restarts the counters again.
 */
void part_round_stats(int cpu, struct hd_struct *part)
{
	unsigned long now = jiffies;

	if (part->partno)
		part_round_stats_single(cpu, &part_to_disk(part)->part0, now);
	part_round_stats_single(cpu, part, now);
}
EXPORT_SYMBOL_GPL(part_round_stats);

/*
 * queue lock must be held
 */
void __blk_put_request(struct request_queue *q, struct request *req)
{
	if (unlikely(!q))
		return;
	if (unlikely(--req->ref_count))
		return;

	elv_completed_request(q, req);

	/* this is a bio leak */
	WARN_ON(req->bio != NULL);

	/*
	 * Request may not have originated from ll_rw_blk. if not,
	 * it didn't come out of our reserved rq pools
	 */
	if (req->cmd_flags & REQ_ALLOCED) {
		int is_sync = rq_is_sync(req) != 0;
		int priv = req->cmd_flags & REQ_ELVPRIV;

		BUG_ON(!list_empty(&req->queuelist));
		BUG_ON(!hlist_unhashed(&req->hash));

		blk_free_request(q, req);
		freed_request(q, is_sync, priv);
	}
}
EXPORT_SYMBOL_GPL(__blk_put_request);

void blk_put_request(struct request *req)
{
	unsigned long flags;
	struct request_queue *q = req->q;

	spin_lock_irqsave(q->queue_lock, flags);
	__blk_put_request(q, req);
	spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(blk_put_request);

/**
 * blk_add_request_payload - add a payload to a request
 * @rq: request to update
 * @page: page backing the payload
 * @len: length of the payload.
 *
 * This allows to later add a payload to an already submitted request by
 * a block driver.  The driver needs to take care of freeing the payload
 * itself.
 *
 * Note that this is a quite horrible hack and nothing but handling of
 * discard requests should ever use it.
 */
void blk_add_request_payload(struct request *rq, struct page *page,
		unsigned int len)
{
	struct bio *bio = rq->bio;

	bio->bi_io_vec->bv_page = page;
	bio->bi_io_vec->bv_offset = 0;
	bio->bi_io_vec->bv_len = len;

	bio->bi_size = len;
	bio->bi_vcnt = 1;
	bio->bi_phys_segments = 1;

	rq->__data_len = rq->resid_len = len;
	rq->nr_phys_segments = 1;
	rq->buffer = bio_data(bio);
}
EXPORT_SYMBOL_GPL(blk_add_request_payload);

static bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
				   struct bio *bio)
{
	const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

	if (!ll_back_merge_fn(q, req, bio))
		return false;

	trace_block_bio_backmerge(q, bio);

	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
		blk_rq_set_mixed_merge(req);

	req->biotail->bi_next = bio;
	req->biotail = bio;
	req->__data_len += bio->bi_size;
	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

	drive_stat_acct(req, 0);
	elv_bio_merged(q, req, bio);
	return true;
}

static bool bio_attempt_front_merge(struct request_queue *q,
				    struct request *req, struct bio *bio)
{
	const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

	if (!ll_front_merge_fn(q, req, bio))
		return false;

	trace_block_bio_frontmerge(q, bio);

	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
		blk_rq_set_mixed_merge(req);

	bio->bi_next = req->bio;
	req->bio = bio;

	/*
	 * may not be valid. if the low level driver said
	 * it didn't need a bounce buffer then it better
	 * not touch req->buffer either...
	 */
	req->buffer = bio_data(bio);
	req->__sector = bio->bi_sector;
	req->__data_len += bio->bi_size;
	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

	drive_stat_acct(req, 0);
	elv_bio_merged(q, req, bio);
	return true;
}

/*
 * Attempts to merge with the plugged list in the current process. Returns
 * true if merge was successful, otherwise false.
 */
static bool attempt_plug_merge(struct task_struct *tsk, struct request_queue *q,
			       struct bio *bio)
{
	struct blk_plug *plug;
	struct request *rq;
	bool ret = false;

	plug = tsk->plug;
	if (!plug)
		goto out;

	list_for_each_entry_reverse(rq, &plug->list, queuelist) {
		int el_ret;

		if (rq->q != q)
			continue;

		el_ret = elv_try_merge(rq, bio);
		if (el_ret == ELEVATOR_BACK_MERGE) {
			ret = bio_attempt_back_merge(q, rq, bio);
			if (ret)
				break;
		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
			ret = bio_attempt_front_merge(q, rq, bio);
			if (ret)
				break;
		}
	}
out:
	return ret;
}

void init_request_from_bio(struct request *req, struct bio *bio)
{
	req->cpu = bio->bi_comp_cpu;
	req->cmd_type = REQ_TYPE_FS;

	req->cmd_flags |= bio->bi_rw & REQ_COMMON_MASK;
	if (bio->bi_rw & REQ_RAHEAD)
		req->cmd_flags |= REQ_FAILFAST_MASK;

	req->errors = 0;
	req->__sector = bio->bi_sector;
	req->ioprio = bio_prio(bio);
	blk_rq_bio_prep(req->q, req, bio);
}

static int __make_request(struct request_queue *q, struct bio *bio)
{
	const bool sync = !!(bio->bi_rw & REQ_SYNC);
	struct blk_plug *plug;
	int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
	struct request *req;

	/*
	 * low level driver can indicate that it wants pages above a
	 * certain limit bounced to low memory (ie for highmem, or even
	 * ISA dma in theory)
	 */
	blk_queue_bounce(q, &bio);

	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
		spin_lock_irq(q->queue_lock);
		where = ELEVATOR_INSERT_FLUSH;
		goto get_rq;
	}

	/*
	 * Check if we can merge with the plugged list before grabbing
	 * any locks.
	 */
	if (attempt_plug_merge(current, q, bio))
		goto out;

	spin_lock_irq(q->queue_lock);

	el_ret = elv_merge(q, &req, bio);
	if (el_ret == ELEVATOR_BACK_MERGE) {
		if (bio_attempt_back_merge(q, req, bio)) {
			if (!attempt_back_merge(q, req))
				elv_merged_request(q, req, el_ret);
			goto out_unlock;
		}
	} else if (el_ret == ELEVATOR_FRONT_MERGE) {
		if (bio_attempt_front_merge(q, req, bio)) {
			if (!attempt_front_merge(q, req))
				elv_merged_request(q, req, el_ret);
			goto out_unlock;
		}
	}

get_rq:
	/*
	 * This sync check and mask will be re-done in init_request_from_bio(),
	 * but we need to set it earlier to expose the sync flag to the
	 * rq allocator and io schedulers.
	 */
	rw_flags = bio_data_dir(bio);
	if (sync)
		rw_flags |= REQ_SYNC;

	/*
	 * Grab a free request. This is might sleep but can not fail.
	 * Returns with the queue unlocked.
	 */
	req = get_request_wait(q, rw_flags, bio);

	/*
	 * After dropping the lock and possibly sleeping here, our request
	 * may now be mergeable after it had proven unmergeable (above).
	 * We don't worry about that case for efficiency. It won't happen
	 * often, and the elevators are able to handle it.
	 */
	init_request_from_bio(req, bio);

	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) ||
	    bio_flagged(bio, BIO_CPU_AFFINE))
		req->cpu = raw_smp_processor_id();

	plug = current->plug;
	if (plug) {
		/*
		 * If this is the first request added after a plug, fire
		 * of a plug trace. If others have been added before, check
		 * if we have multiple devices in this plug. If so, make a
		 * note to sort the list before dispatch.
		 */
		if (list_empty(&plug->list))
			trace_block_plug(q);
		else if (!plug->should_sort) {
			struct request *__rq;

			__rq = list_entry_rq(plug->list.prev);
			if (__rq->q != q)
				plug->should_sort = 1;
		}
		list_add_tail(&req->queuelist, &plug->list);
		plug->count++;
		drive_stat_acct(req, 1);
		if (plug->count >= BLK_MAX_REQUEST_COUNT)
			blk_flush_plug_list(plug, false);
	} else {
		spin_lock_irq(q->queue_lock);
		add_acct_request(q, req, where);
		__blk_run_queue(q);
out_unlock:
		spin_unlock_irq(q->queue_lock);
	}
out:
	return 0;
}

/*
 * If bio->bi_dev is a partition, remap the location
 */
static inline void blk_partition_remap(struct bio *bio)
{
	struct block_device *bdev = bio->bi_bdev;

	if (bio_sectors(bio) && bdev != bdev->bd_contains) {
		struct hd_struct *p = bdev->bd_part;

		bio->bi_sector += p->start_sect;
		bio->bi_bdev = bdev->bd_contains;

		trace_block_bio_remap(bdev_get_queue(bio->bi_bdev), bio,
				      bdev->bd_dev,
				      bio->bi_sector - p->start_sect);
	}
}

static void handle_bad_sector(struct bio *bio)
{
	char b[BDEVNAME_SIZE];

	printk(KERN_INFO "attempt to access beyond end of device\n");
	printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
			bdevname(bio->bi_bdev, b),
			bio->bi_rw,
			(unsigned long long)bio->bi_sector + bio_sectors(bio),
			(long long)(i_size_read(bio->bi_bdev->bd_inode) >> 9));

	set_bit(BIO_EOF, &bio->bi_flags);
}

#ifdef CONFIG_FAIL_MAKE_REQUEST

static DECLARE_FAULT_ATTR(fail_make_request);

static int __init setup_fail_make_request(char *str)
{
	return setup_fault_attr(&fail_make_request, str);
}
__setup("fail_make_request=", setup_fail_make_request);

static bool should_fail_request(struct hd_struct *part, unsigned int bytes)
{
	return part->make_it_fail && should_fail(&fail_make_request, bytes);
}

static int __init fail_make_request_debugfs(void)
{
	struct dentry *dir = fault_create_debugfs_attr("fail_make_request",
						NULL, &fail_make_request);

	return IS_ERR(dir) ? PTR_ERR(dir) : 0;
}

late_initcall(fail_make_request_debugfs);

#else /* CONFIG_FAIL_MAKE_REQUEST */

static inline bool should_fail_request(struct hd_struct *part,
					unsigned int bytes)
{
	return false;
}

#endif /* CONFIG_FAIL_MAKE_REQUEST */

/*
 * Check whether this bio extends beyond the end of the device.
 */
static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
{
	sector_t maxsector;

	if (!nr_sectors)
		return 0;

	/* Test device or partition size, when known. */
	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
	if (maxsector) {
		sector_t sector = bio->bi_sector;

		if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
			/*
			 * This may well happen - the kernel calls bread()
			 * without checking the size of the device, e.g., when
			 * mounting a device.
			 */
			handle_bad_sector(bio);
			return 1;
		}
	}

	return 0;
}

/**
 * generic_make_request - hand a buffer to its device driver for I/O
 * @bio:  The bio describing the location in memory and on the device.
 *
 * generic_make_request() is used to make I/O requests of block
 * devices. It is passed a &struct bio, which describes the I/O that needs
 * to be done.
 *
 * generic_make_request() does not return any status.  The
 * success/failure status of the request, along with notification of
 * completion, is delivered asynchronously through the bio->bi_end_io
 * function described (one day) else where.
 *
 * The caller of generic_make_request must make sure that bi_io_vec
 * are set to describe the memory buffer, and that bi_dev and bi_sector are
 * set to describe the device address, and the
 * bi_end_io and optionally bi_private are set to describe how
 * completion notification should be signaled.
 *
 * generic_make_request and the drivers it calls may use bi_next if this
 * bio happens to be merged with someone else, and may change bi_dev and
 * bi_sector for remaps as it sees fit.  So the values of these fields
 * should NOT be depended on after the call to generic_make_request.
 */
static inline void __generic_make_request(struct bio *bio)
{
	struct request_queue *q;
	sector_t old_sector;
	int ret, nr_sectors = bio_sectors(bio);
	dev_t old_dev;
	int err = -EIO;

	might_sleep();

	if (bio_check_eod(bio, nr_sectors))
		goto end_io;

	/*
	 * Resolve the mapping until finished. (drivers are
	 * still free to implement/resolve their own stacking
	 * by explicitly returning 0)
	 *
	 * NOTE: we don't repeat the blk_size check for each new device.
	 * Stacking drivers are expected to know what they are doing.
	 */
	old_sector = -1;
	old_dev = 0;
	do {
		char b[BDEVNAME_SIZE];
		struct hd_struct *part;

		q = bdev_get_queue(bio->bi_bdev);
		if (unlikely(!q)) {
			printk(KERN_ERR
			       "generic_make_request: Trying to access "
				"nonexistent block-device %s (%Lu)\n",
				bdevname(bio->bi_bdev, b),
				(long long) bio->bi_sector);
			goto end_io;
		}

		if (unlikely(!(bio->bi_rw & REQ_DISCARD) &&
			     nr_sectors > queue_max_hw_sectors(q))) {
			printk(KERN_ERR "bio too big device %s (%u > %u)\n",
			       bdevname(bio->bi_bdev, b),
			       bio_sectors(bio),
			       queue_max_hw_sectors(q));
			goto end_io;
		}

		if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
			goto end_io;

		part = bio->bi_bdev->bd_part;
		if (should_fail_request(part, bio->bi_size) ||
		    should_fail_request(&part_to_disk(part)->part0,
					bio->bi_size))
			goto end_io;

		/*
		 * If this device has partitions, remap block n
		 * of partition p to block n+start(p) of the disk.
		 */
		blk_partition_remap(bio);

		if (bio_integrity_enabled(bio) && bio_integrity_prep(bio))
			goto end_io;

		if (old_sector != -1)
			trace_block_bio_remap(q, bio, old_dev, old_sector);

		old_sector = bio->bi_sector;
		old_dev = bio->bi_bdev->bd_dev;

		if (bio_check_eod(bio, nr_sectors))
			goto end_io;

		/*
		 * Filter flush bio's early so that make_request based
		 * drivers without flush support don't have to worry
		 * about them.
		 */
		if ((bio->bi_rw & (REQ_FLUSH | REQ_FUA)) && !q->flush_flags) {
			bio->bi_rw &= ~(REQ_FLUSH | REQ_FUA);
			if (!nr_sectors) {
				err = 0;
				goto end_io;
			}
		}

		if ((bio->bi_rw & REQ_DISCARD) &&
		    (!blk_queue_discard(q) ||
		     ((bio->bi_rw & REQ_SECURE) &&
		      !blk_queue_secdiscard(q)))) {
			err = -EOPNOTSUPP;
			goto end_io;
		}

		if (blk_throtl_bio(q, &bio))
			goto end_io;

		/*
		 * If bio = NULL, bio has been throttled and will be submitted
		 * later.
		 */
		if (!bio)
			break;

		trace_block_bio_queue(q, bio);

		ret = q->make_request_fn(q, bio);
	} while (ret);

	return;

end_io:
	bio_endio(bio, err);
}

/*
 * We only want one ->make_request_fn to be active at a time,
 * else stack usage with stacked devices could be a problem.
 * So use current->bio_list to keep a list of requests
 * submited by a make_request_fn function.
 * current->bio_list is also used as a flag to say if
 * generic_make_request is currently active in this task or not.
 * If it is NULL, then no make_request is active.  If it is non-NULL,
 * then a make_request is active, and new requests should be added
 * at the tail
 */
void generic_make_request(struct bio *bio)
{
	struct bio_list bio_list_on_stack;

	if (current->bio_list) {
		/* make_request is active */
		bio_list_add(current->bio_list, bio);
		return;
	}
	/* following loop may be a bit non-obvious, and so deserves some
	 * explanation.
	 * Before entering the loop, bio->bi_next is NULL (as all callers
	 * ensure that) so we have a list with a single bio.
	 * We pretend that we have just taken it off a longer list, so
	 * we assign bio_list to a pointer to the bio_list_on_stack,
	 * thus initialising the bio_list of new bios to be
	 * added.  __generic_make_request may indeed add some more bios
	 * through a recursive call to generic_make_request.  If it
	 * did, we find a non-NULL value in bio_list and re-enter the loop
	 * from the top.  In this case we really did just take the bio
	 * of the top of the list (no pretending) and so remove it from
	 * bio_list, and call into __generic_make_request again.
	 *
	 * The loop was structured like this to make only one call to
	 * __generic_make_request (which is important as it is large and
	 * inlined) and to keep the structure simple.
	 */
	BUG_ON(bio->bi_next);
	bio_list_init(&bio_list_on_stack);
	current->bio_list = &bio_list_on_stack;
	do {
		__generic_make_request(bio);
		bio = bio_list_pop(current->bio_list);
	} while (bio);
	current->bio_list = NULL; /* deactivate */
}
EXPORT_SYMBOL(generic_make_request);

/**
 * submit_bio - submit a bio to the block device layer for I/O
 * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
 * @bio: The &struct bio which describes the I/O
 *
 * submit_bio() is very similar in purpose to generic_make_request(), and
 * uses that function to do most of the work. Both are fairly rough
 * interfaces; @bio must be presetup and ready for I/O.
 *
 */
void submit_bio(int rw, struct bio *bio)
{
	int count = bio_sectors(bio);

	bio->bi_rw |= rw;

	/*
	 * If it's a regular read/write or a barrier with data attached,
	 * go through the normal accounting stuff before submission.
	 */
	if (bio_has_data(bio) && !(rw & REQ_DISCARD)) {
		if (rw & WRITE) {
			count_vm_events(PGPGOUT, count);
		} else {
			task_io_account_read(bio->bi_size);
			count_vm_events(PGPGIN, count);
		}

		if (unlikely(block_dump)) {
			char b[BDEVNAME_SIZE];
			printk(KERN_DEBUG "%s(%d): %s block %Lu on %s (%u sectors)\n",
			current->comm, task_pid_nr(current),
				(rw & WRITE) ? "WRITE" : "READ",
				(unsigned long long)bio->bi_sector,
				bdevname(bio->bi_bdev, b),
				count);
		}
	}

	generic_make_request(bio);
}
EXPORT_SYMBOL(submit_bio);

/**
 * blk_rq_check_limits - Helper function to check a request for the queue limit
 * @q:  the queue
 * @rq: the request being checked
 *
 * Description:
 *    @rq may have been made based on weaker limitations of upper-level queues
 *    in request stacking drivers, and it may violate the limitation of @q.
 *    Since the block layer and the underlying device driver trust @rq
 *    after it is inserted to @q, it should be checked against @q before
 *    the insertion using this generic function.
 *
 *    This function should also be useful for request stacking drivers
 *    in some cases below, so export this function.
 *    Request stacking drivers like request-based dm may change the queue
 *    limits while requests are in the queue (e.g. dm's table swapping).
 *    Such request stacking drivers should check those requests agaist
 *    the new queue limits again when they dispatch those requests,
 *    although such checkings are also done against the old queue limits
 *    when submitting requests.
 */
int blk_rq_check_limits(struct request_queue *q, struct request *rq)
{
	if (rq->cmd_flags & REQ_DISCARD)
		return 0;

	if (blk_rq_sectors(rq) > queue_max_sectors(q) ||
	    blk_rq_bytes(rq) > queue_max_hw_sectors(q) << 9) {
		printk(KERN_ERR "%s: over max size limit.\n", __func__);
		return -EIO;
	}

	/*
	 * queue's settings related to segment counting like q->bounce_pfn
	 * may differ from that of other stacking queues.
	 * Recalculate it to check the request correctly on this queue's
	 * limitation.
	 */
	blk_recalc_rq_segments(rq);
	if (rq->nr_phys_segments > queue_max_segments(q)) {
		printk(KERN_ERR "%s: over max segments limit.\n", __func__);
		return -EIO;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(blk_rq_check_limits);

/**
 * blk_insert_cloned_request - Helper for stacking drivers to submit a request
 * @q:  the queue to submit the request
 * @rq: the request being queued
 */
int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
{
	unsigned long flags;
	int where = ELEVATOR_INSERT_BACK;

	if (blk_rq_check_limits(q, rq))
		return -EIO;

	if (rq->rq_disk &&
	    should_fail_request(&rq->rq_disk->part0, blk_rq_bytes(rq)))
		return -EIO;

	spin_lock_irqsave(q->queue_lock, flags);

	/*
	 * Submitting request must be dequeued before calling this function
	 * because it will be linked to another request_queue
	 */
	BUG_ON(blk_queued_rq(rq));

	if (rq->cmd_flags & (REQ_FLUSH|REQ_FUA))
		where = ELEVATOR_INSERT_FLUSH;

	add_acct_request(q, rq, where);
	spin_unlock_irqrestore(q->queue_lock, flags);

	return 0;
}
EXPORT_SYMBOL_GPL(blk_insert_cloned_request);

/**
 * blk_rq_err_bytes - determine number of bytes till the next failure boundary
 * @rq: request to examine
 *
 * Description:
 *     A request could be merge of IOs which require different failure
 *     handling.  This function determines the number of bytes which
 *     can be failed from the beginning of the request without
 *     crossing into area which need to be retried further.
 *
 * Return:
 *     The number of bytes to fail.
 *
 * Context:
 *     queue_lock must be held.
 */
unsigned int blk_rq_err_bytes(const struct request *rq)
{
	unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
	unsigned int bytes = 0;
	struct bio *bio;

	if (!(rq->cmd_flags & REQ_MIXED_MERGE))
		return blk_rq_bytes(rq);

	/*
	 * Currently the only 'mixing' which can happen is between
	 * different fastfail types.  We can safely fail portions
	 * which have all the failfast bits that the first one has -
	 * the ones which are at least as eager to fail as the first
	 * one.
	 */
	for (bio = rq->bio; bio; bio = bio->bi_next) {
		if ((bio->bi_rw & ff) != ff)
			break;
		bytes += bio->bi_size;
	}

	/* this could lead to infinite loop */
	BUG_ON(blk_rq_bytes(rq) && !bytes);
	return bytes;
}
EXPORT_SYMBOL_GPL(blk_rq_err_bytes);

static void blk_account_io_completion(struct request *req, unsigned int bytes)
{
	if (blk_do_io_stat(req)) {
		const int rw = rq_data_dir(req);
		struct hd_struct *part;
		int cpu;

		cpu = part_stat_lock();
		part = req->part;
		part_stat_add(cpu, part, sectors[rw], bytes >> 9);
		part_stat_unlock();
	}
}

static void blk_account_io_done(struct request *req)
{
	/*
	 * Account IO completion.  flush_rq isn't accounted as a
	 * normal IO on queueing nor completion.  Accounting the
	 * containing request is enough.
	 */
	if (blk_do_io_stat(req) && !(req->cmd_flags & REQ_FLUSH_SEQ)) {
		unsigned long duration = jiffies - req->start_time;
		const int rw = rq_data_dir(req);
		struct hd_struct *part;
		int cpu;

		cpu = part_stat_lock();
		part = req->part;

		part_stat_inc(cpu, part, ios[rw]);
		part_stat_add(cpu, part, ticks[rw], duration);
		part_round_stats(cpu, part);
		part_dec_in_flight(part, rw);

		hd_struct_put(part);
		part_stat_unlock();
	}
}

/**
 * blk_peek_request - peek at the top of a request queue
 * @q: request queue to peek at
 *
 * Description:
 *     Return the request at the top of @q.  The returned request
 *     should be started using blk_start_request() before LLD starts
 *     processing it.
 *
 * Return:
 *     Pointer to the request at the top of @q if available.  Null
 *     otherwise.
 *
 * Context:
 *     queue_lock must be held.
 */
struct request *blk_peek_request(struct request_queue *q)
{
	struct request *rq;
	int ret;

	while ((rq = __elv_next_request(q)) != NULL) {
		if (!(rq->cmd_flags & REQ_STARTED)) {
			/*
			 * This is the first time the device driver
			 * sees this request (possibly after
			 * requeueing).  Notify IO scheduler.
			 */
			if (rq->cmd_flags & REQ_SORTED)
				elv_activate_rq(q, rq);

			/*
			 * just mark as started even if we don't start
			 * it, a request that has been delayed should
			 * not be passed by new incoming requests
			 */
			rq->cmd_flags |= REQ_STARTED;
			trace_block_rq_issue(q, rq);
		}

		if (!q->boundary_rq || q->boundary_rq == rq) {
			q->end_sector = rq_end_sector(rq);
			q->boundary_rq = NULL;
		}

		if (rq->cmd_flags & REQ_DONTPREP)
			break;

		if (q->dma_drain_size && blk_rq_bytes(rq)) {
			/*
			 * make sure space for the drain appears we
			 * know we can do this because max_hw_segments
			 * has been adjusted to be one fewer than the
			 * device can handle
			 */
			rq->nr_phys_segments++;
		}

		if (!q->prep_rq_fn)
			break;

		ret = q->prep_rq_fn(q, rq);
		if (ret == BLKPREP_OK) {
			break;
		} else if (ret == BLKPREP_DEFER) {
			/*
			 * the request may have been (partially) prepped.
			 * we need to keep this request in the front to
			 * avoid resource deadlock.  REQ_STARTED will
			 * prevent other fs requests from passing this one.
			 */
			if (q->dma_drain_size && blk_rq_bytes(rq) &&
			    !(rq->cmd_flags & REQ_DONTPREP)) {
				/*
				 * remove the space for the drain we added
				 * so that we don't add it again
				 */
				--rq->nr_phys_segments;
			}

			rq = NULL;
			break;
		} else if (ret == BLKPREP_KILL) {
			rq->cmd_flags |= REQ_QUIET;
			/*
			 * Mark this request as started so we don't trigger
			 * any debug logic in the end I/O path.
			 */
			blk_start_request(rq);
			__blk_end_request_all(rq, -EIO);
		} else {
			printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
			break;
		}
	}

	return rq;
}
EXPORT_SYMBOL(blk_peek_request);

void blk_dequeue_request(struct request *rq)
{
	struct request_queue *q = rq->q;

	BUG_ON(list_empty(&rq->queuelist));
	BUG_ON(ELV_ON_HASH(rq));

	list_del_init(&rq->queuelist);

	/*
	 * the time frame between a request being removed from the lists
	 * and to it is freed is accounted as io that is in progress at
	 * the driver side.
	 */
	if (blk_account_rq(rq)) {
		q->in_flight[rq_is_sync(rq)]++;
		set_io_start_time_ns(rq);
	}
}

/**
 * blk_start_request - start request processing on the driver
 * @req: request to dequeue
 *
 * Description:
 *     Dequeue @req and start timeout timer on it.  This hands off the
 *     request to the driver.
 *
 *     Block internal functions which don't want to start timer should
 *     call blk_dequeue_request().
 *
 * Context:
 *     queue_lock must be held.
 */
void blk_start_request(struct request *req)
{
	blk_dequeue_request(req);

	/*
	 * We are now handing the request to the hardware, initialize
	 * resid_len to full count and add the timeout handler.
	 */
	req->resid_len = blk_rq_bytes(req);
	if (unlikely(blk_bidi_rq(req)))
		req->next_rq->resid_len = blk_rq_bytes(req->next_rq);

	blk_add_timer(req);
}
EXPORT_SYMBOL(blk_start_request);

/**
 * blk_fetch_request - fetch a request from a request queue
 * @q: request queue to fetch a request from
 *
 * Description:
 *     Return the request at the top of @q.  The request is started on
 *     return and LLD can start processing it immediately.
 *
 * Return:
 *     Pointer to the request at the top of @q if available.  Null
 *     otherwise.
 *
 * Context:
 *     queue_lock must be held.
 */
struct request *blk_fetch_request(struct request_queue *q)
{
	struct request *rq;

	rq = blk_peek_request(q);
	if (rq)
		blk_start_request(rq);
	return rq;
}
EXPORT_SYMBOL(blk_fetch_request);

/**
 * blk_update_request - Special helper function for request stacking drivers
 * @req:      the request being processed
 * @error:    %0 for success, < %0 for error
 * @nr_bytes: number of bytes to complete @req
 *
 * Description:
 *     Ends I/O on a number of bytes attached to @req, but doesn't complete
 *     the request structure even if @req doesn't have leftover.
 *     If @req has leftover, sets it up for the next range of segments.
 *
 *     This special helper function is only for request stacking drivers
 *     (e.g. request-based dm) so that they can handle partial completion.
 *     Actual device drivers should use blk_end_request instead.
 *
 *     Passing the result of blk_rq_bytes() as @nr_bytes guarantees
 *     %false return from this function.
 *
 * Return:
 *     %false - this request doesn't have any more data
 *     %true  - this request has more data
 **/
bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
{
	int total_bytes, bio_nbytes, next_idx = 0;
	struct bio *bio;

	if (!req->bio)
		return false;

	trace_block_rq_complete(req->q, req);

	/*
	 * For fs requests, rq is just carrier of independent bio's
	 * and each partial completion should be handled separately.
	 * Reset per-request error on each partial completion.
	 *
	 * TODO: tj: This is too subtle.  It would be better to let
	 * low level drivers do what they see fit.
	 */
	if (req->cmd_type == REQ_TYPE_FS)
		req->errors = 0;

	if (error && req->cmd_type == REQ_TYPE_FS &&
	    !(req->cmd_flags & REQ_QUIET)) {
		char *error_type;

		switch (error) {
		case -ENOLINK:
			error_type = "recoverable transport";
			break;
		case -EREMOTEIO:
			error_type = "critical target";
			break;
		case -EBADE:
			error_type = "critical nexus";
			break;
		case -EIO:
		default:
			error_type = "I/O";
			break;
		}
		printk(KERN_ERR "end_request: %s error, dev %s, sector %llu\n",
		       error_type, req->rq_disk ? req->rq_disk->disk_name : "?",
		       (unsigned long long)blk_rq_pos(req));
	}

	blk_account_io_completion(req, nr_bytes);

	total_bytes = bio_nbytes = 0;
	while ((bio = req->bio) != NULL) {
		int nbytes;

		if (nr_bytes >= bio->bi_size) {
			req->bio = bio->bi_next;
			nbytes = bio->bi_size;
			req_bio_endio(req, bio, nbytes, error);
			next_idx = 0;
			bio_nbytes = 0;
		} else {
			int idx = bio->bi_idx + next_idx;

			if (unlikely(idx >= bio->bi_vcnt)) {
				blk_dump_rq_flags(req, "__end_that");
				printk(KERN_ERR "%s: bio idx %d >= vcnt %d\n",
				       __func__, idx, bio->bi_vcnt);
				break;
			}

			nbytes = bio_iovec_idx(bio, idx)->bv_len;
			BIO_BUG_ON(nbytes > bio->bi_size);

			/*
			 * not a complete bvec done
			 */
			if (unlikely(nbytes > nr_bytes)) {
				bio_nbytes += nr_bytes;
				total_bytes += nr_bytes;
				break;
			}

			/*
			 * advance to the next vector
			 */
			next_idx++;
			bio_nbytes += nbytes;
		}

		total_bytes += nbytes;
		nr_bytes -= nbytes;

		bio = req->bio;
		if (bio) {
			/*
			 * end more in this run, or just return 'not-done'
			 */
			if (unlikely(nr_bytes <= 0))
				break;
		}
	}

	/*
	 * completely done
	 */
	if (!req->bio) {
		/*
		 * Reset counters so that the request stacking driver
		 * can find how many bytes remain in the request
		 * later.
		 */
		req->__data_len = 0;
		return false;
	}

	/*
	 * if the request wasn't completed, update state
	 */
	if (bio_nbytes) {
		req_bio_endio(req, bio, bio_nbytes, error);
		bio->bi_idx += next_idx;
		bio_iovec(bio)->bv_offset += nr_bytes;
		bio_iovec(bio)->bv_len -= nr_bytes;
	}

	req->__data_len -= total_bytes;
	req->buffer = bio_data(req->bio);

	/* update sector only for requests with clear definition of sector */
	if (req->cmd_type == REQ_TYPE_FS || (req->cmd_flags & REQ_DISCARD))
		req->__sector += total_bytes >> 9;

	/* mixed attributes always follow the first bio */
	if (req->cmd_flags & REQ_MIXED_MERGE) {
		req->cmd_flags &= ~REQ_FAILFAST_MASK;
		req->cmd_flags |= req->bio->bi_rw & REQ_FAILFAST_MASK;
	}

	/*
	 * If total number of sectors is less than the first segment
	 * size, something has gone terribly wrong.
	 */
	if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
		blk_dump_rq_flags(req, "request botched");
		req->__data_len = blk_rq_cur_bytes(req);
	}

	/* recalculate the number of segments */
	blk_recalc_rq_segments(req);

	return true;
}
EXPORT_SYMBOL_GPL(blk_update_request);

static bool blk_update_bidi_request(struct request *rq, int error,
				    unsigned int nr_bytes,
				    unsigned int bidi_bytes)
{
	if (blk_update_request(rq, error, nr_bytes))
		return true;

	/* Bidi request must be completed as a whole */
	if (unlikely(blk_bidi_rq(rq)) &&
	    blk_update_request(rq->next_rq, error, bidi_bytes))
		return true;

	if (blk_queue_add_random(rq->q))
		add_disk_randomness(rq->rq_disk);

	return false;
}

/**
 * blk_unprep_request - unprepare a request
 * @req:	the request
 *
 * This function makes a request ready for complete resubmission (or
 * completion).  It happens only after all error handling is complete,
 * so represents the appropriate moment to deallocate any resources
 * that were allocated to the request in the prep_rq_fn.  The queue
 * lock is held when calling this.
 */
void blk_unprep_request(struct request *req)
{
	struct request_queue *q = req->q;

	req->cmd_flags &= ~REQ_DONTPREP;
	if (q->unprep_rq_fn)
		q->unprep_rq_fn(q, req);
}
EXPORT_SYMBOL_GPL(blk_unprep_request);

/*
 * queue lock must be held
 */
static void blk_finish_request(struct request *req, int error)
{
	if (blk_rq_tagged(req))
		blk_queue_end_tag(req->q, req);

	BUG_ON(blk_queued_rq(req));

	if (unlikely(laptop_mode) && req->cmd_type == REQ_TYPE_FS)
		laptop_io_completion(&req->q->backing_dev_info);

	blk_delete_timer(req);

	if (req->cmd_flags & REQ_DONTPREP)
		blk_unprep_request(req);


	blk_account_io_done(req);

	if (req->end_io)
		req->end_io(req, error);
	else {
		if (blk_bidi_rq(req))
			__blk_put_request(req->next_rq->q, req->next_rq);

		__blk_put_request(req->q, req);
	}
}

/**
 * blk_end_bidi_request - Complete a bidi request
 * @rq:         the request to complete
 * @error:      %0 for success, < %0 for error
 * @nr_bytes:   number of bytes to complete @rq
 * @bidi_bytes: number of bytes to complete @rq->next_rq
 *
 * Description:
 *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
 *     Drivers that supports bidi can safely call this member for any
 *     type of request, bidi or uni.  In the later case @bidi_bytes is
 *     just ignored.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 **/
static bool blk_end_bidi_request(struct request *rq, int error,
				 unsigned int nr_bytes, unsigned int bidi_bytes)
{
	struct request_queue *q = rq->q;
	unsigned long flags;

	if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
		return true;

	spin_lock_irqsave(q->queue_lock, flags);
	blk_finish_request(rq, error);
	spin_unlock_irqrestore(q->queue_lock, flags);

	return false;
}

/**
 * __blk_end_bidi_request - Complete a bidi request with queue lock held
 * @rq:         the request to complete
 * @error:      %0 for success, < %0 for error
 * @nr_bytes:   number of bytes to complete @rq
 * @bidi_bytes: number of bytes to complete @rq->next_rq
 *
 * Description:
 *     Identical to blk_end_bidi_request() except that queue lock is
 *     assumed to be locked on entry and remains so on return.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 **/
bool __blk_end_bidi_request(struct request *rq, int error,
				   unsigned int nr_bytes, unsigned int bidi_bytes)
{
	if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
		return true;

	blk_finish_request(rq, error);

	return false;
}

/**
 * blk_end_request - Helper function for drivers to complete the request.
 * @rq:       the request being processed
 * @error:    %0 for success, < %0 for error
 * @nr_bytes: number of bytes to complete
 *
 * Description:
 *     Ends I/O on a number of bytes attached to @rq.
 *     If @rq has leftover, sets it up for the next range of segments.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 **/
bool blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
{
	return blk_end_bidi_request(rq, error, nr_bytes, 0);
}
EXPORT_SYMBOL(blk_end_request);

/**
 * blk_end_request_all - Helper function for drives to finish the request.
 * @rq: the request to finish
 * @error: %0 for success, < %0 for error
 *
 * Description:
 *     Completely finish @rq.
 */
void blk_end_request_all(struct request *rq, int error)
{
	bool pending;
	unsigned int bidi_bytes = 0;

	if (unlikely(blk_bidi_rq(rq)))
		bidi_bytes = blk_rq_bytes(rq->next_rq);

	pending = blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
	BUG_ON(pending);
}
EXPORT_SYMBOL(blk_end_request_all);

/**
 * blk_end_request_cur - Helper function to finish the current request chunk.
 * @rq: the request to finish the current chunk for
 * @error: %0 for success, < %0 for error
 *
 * Description:
 *     Complete the current consecutively mapped chunk from @rq.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 */
bool blk_end_request_cur(struct request *rq, int error)
{
	return blk_end_request(rq, error, blk_rq_cur_bytes(rq));
}
EXPORT_SYMBOL(blk_end_request_cur);

/**
 * blk_end_request_err - Finish a request till the next failure boundary.
 * @rq: the request to finish till the next failure boundary for
 * @error: must be negative errno
 *
 * Description:
 *     Complete @rq till the next failure boundary.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 */
bool blk_end_request_err(struct request *rq, int error)
{
	WARN_ON(error >= 0);
	return blk_end_request(rq, error, blk_rq_err_bytes(rq));
}
EXPORT_SYMBOL_GPL(blk_end_request_err);

/**
 * __blk_end_request - Helper function for drivers to complete the request.
 * @rq:       the request being processed
 * @error:    %0 for success, < %0 for error
 * @nr_bytes: number of bytes to complete
 *
 * Description:
 *     Must be called with queue lock held unlike blk_end_request().
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 **/
bool __blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
{
	return __blk_end_bidi_request(rq, error, nr_bytes, 0);
}
EXPORT_SYMBOL(__blk_end_request);

/**
 * __blk_end_request_all - Helper function for drives to finish the request.
 * @rq: the request to finish
 * @error: %0 for success, < %0 for error
 *
 * Description:
 *     Completely finish @rq.  Must be called with queue lock held.
 */
void __blk_end_request_all(struct request *rq, int error)
{
	bool pending;
	unsigned int bidi_bytes = 0;

	if (unlikely(blk_bidi_rq(rq)))
		bidi_bytes = blk_rq_bytes(rq->next_rq);

	pending = __blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
	BUG_ON(pending);
}
EXPORT_SYMBOL(__blk_end_request_all);

/**
 * __blk_end_request_cur - Helper function to finish the current request chunk.
 * @rq: the request to finish the current chunk for
 * @error: %0 for success, < %0 for error
 *
 * Description:
 *     Complete the current consecutively mapped chunk from @rq.  Must
 *     be called with queue lock held.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 */
bool __blk_end_request_cur(struct request *rq, int error)
{
	return __blk_end_request(rq, error, blk_rq_cur_bytes(rq));
}
EXPORT_SYMBOL(__blk_end_request_cur);

/**
 * __blk_end_request_err - Finish a request till the next failure boundary.
 * @rq: the request to finish till the next failure boundary for
 * @error: must be negative errno
 *
 * Description:
 *     Complete @rq till the next failure boundary.  Must be called
 *     with queue lock held.
 *
 * Return:
 *     %false - we are done with this request
 *     %true  - still buffers pending for this request
 */
bool __blk_end_request_err(struct request *rq, int error)
{
	WARN_ON(error >= 0);
	return __blk_end_request(rq, error, blk_rq_err_bytes(rq));
}
EXPORT_SYMBOL_GPL(__blk_end_request_err);

void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
		     struct bio *bio)
{
	/* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw */
	rq->cmd_flags |= bio->bi_rw & REQ_WRITE;

	if (bio_has_data(bio)) {
		rq->nr_phys_segments = bio_phys_segments(q, bio);
		rq->buffer = bio_data(bio);
	}
	rq->__data_len = bio->bi_size;
	rq->bio = rq->biotail = bio;

	if (bio->bi_bdev)
		rq->rq_disk = bio->bi_bdev->bd_disk;
}

#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
/**
 * rq_flush_dcache_pages - Helper function to flush all pages in a request
 * @rq: the request to be flushed
 *
 * Description:
 *     Flush all pages in @rq.
 */
void rq_flush_dcache_pages(struct request *rq)
{
	struct req_iterator iter;
	struct bio_vec *bvec;

	rq_for_each_segment(bvec, rq, iter)
		flush_dcache_page(bvec->bv_page);
}
EXPORT_SYMBOL_GPL(rq_flush_dcache_pages);
#endif

/**
 * blk_lld_busy - Check if underlying low-level drivers of a device are busy
 * @q : the queue of the device being checked
 *
 * Description:
 *    Check if underlying low-level drivers of a device are busy.
 *    If the drivers want to export their busy state, they must set own
 *    exporting function using blk_queue_lld_busy() first.
 *
 *    Basically, this function is used only by request stacking drivers
 *    to stop dispatching requests to underlying devices when underlying
 *    devices are busy.  This behavior helps more I/O merging on the queue
 *    of the request stacking driver and prevents I/O throughput regression
 *    on burst I/O load.
 *
 * Return:
 *    0 - Not busy (The request stacking driver should dispatch request)
 *    1 - Busy (The request stacking driver should stop dispatching request)
 */
int blk_lld_busy(struct request_queue *q)
{
	if (q->lld_busy_fn)
		return q->lld_busy_fn(q);

	return 0;
}
EXPORT_SYMBOL_GPL(blk_lld_busy);

/**
 * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
 * @rq: the clone request to be cleaned up
 *
 * Description:
 *     Free all bios in @rq for a cloned request.
 */
void blk_rq_unprep_clone(struct request *rq)
{
	struct bio *bio;

	while ((bio = rq->bio) != NULL) {
		rq->bio = bio->bi_next;

		bio_put(bio);
	}
}
EXPORT_SYMBOL_GPL(blk_rq_unprep_clone);

/*
 * Copy attributes of the original request to the clone request.
 * The actual data parts (e.g. ->cmd, ->buffer, ->sense) are not copied.
 */
static void __blk_rq_prep_clone(struct request *dst, struct request *src)
{
	dst->cpu = src->cpu;
	dst->cmd_flags = (src->cmd_flags & REQ_CLONE_MASK) | REQ_NOMERGE;
	dst->cmd_type = src->cmd_type;
	dst->__sector = blk_rq_pos(src);
	dst->__data_len = blk_rq_bytes(src);
	dst->nr_phys_segments = src->nr_phys_segments;
	dst->ioprio = src->ioprio;
	dst->extra_len = src->extra_len;
}

/**
 * blk_rq_prep_clone - Helper function to setup clone request
 * @rq: the request to be setup
 * @rq_src: original request to be cloned
 * @bs: bio_set that bios for clone are allocated from
 * @gfp_mask: memory allocation mask for bio
 * @bio_ctr: setup function to be called for each clone bio.
 *           Returns %0 for success, non %0 for failure.
 * @data: private data to be passed to @bio_ctr
 *
 * Description:
 *     Clones bios in @rq_src to @rq, and copies attributes of @rq_src to @rq.
 *     The actual data parts of @rq_src (e.g. ->cmd, ->buffer, ->sense)
 *     are not copied, and copying such parts is the caller's responsibility.
 *     Also, pages which the original bios are pointing to are not copied
 *     and the cloned bios just point same pages.
 *     So cloned bios must be completed before original bios, which means
 *     the caller must complete @rq before @rq_src.
 */
int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
		      struct bio_set *bs, gfp_t gfp_mask,
		      int (*bio_ctr)(struct bio *, struct bio *, void *),
		      void *data)
{
	struct bio *bio, *bio_src;

	if (!bs)
		bs = fs_bio_set;

	blk_rq_init(NULL, rq);

	__rq_for_each_bio(bio_src, rq_src) {
		bio = bio_alloc_bioset(gfp_mask, bio_src->bi_max_vecs, bs);
		if (!bio)
			goto free_and_out;

		__bio_clone(bio, bio_src);

		if (bio_integrity(bio_src) &&
		    bio_integrity_clone(bio, bio_src, gfp_mask, bs))
			goto free_and_out;

		if (bio_ctr && bio_ctr(bio, bio_src, data))
			goto free_and_out;

		if (rq->bio) {
			rq->biotail->bi_next = bio;
			rq->biotail = bio;
		} else
			rq->bio = rq->biotail = bio;
	}

	__blk_rq_prep_clone(rq, rq_src);

	return 0;

free_and_out:
	if (bio)
		bio_free(bio, bs);
	blk_rq_unprep_clone(rq);

	return -ENOMEM;
}
EXPORT_SYMBOL_GPL(blk_rq_prep_clone);

int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
{
	return queue_work(kblockd_workqueue, work);
}
EXPORT_SYMBOL(kblockd_schedule_work);

int kblockd_schedule_delayed_work(struct request_queue *q,
			struct delayed_work *dwork, unsigned long delay)
{
	return queue_delayed_work(kblockd_workqueue, dwork, delay);
}
EXPORT_SYMBOL(kblockd_schedule_delayed_work);

#define PLUG_MAGIC	0x91827364

void blk_start_plug(struct blk_plug *plug)
{
	struct task_struct *tsk = current;

	plug->magic = PLUG_MAGIC;
	INIT_LIST_HEAD(&plug->list);
	INIT_LIST_HEAD(&plug->cb_list);
	plug->should_sort = 0;
	plug->count = 0;

	/*
	 * If this is a nested plug, don't actually assign it. It will be
	 * flushed on its own.
	 */
	if (!tsk->plug) {
		/*
		 * Store ordering should not be needed here, since a potential
		 * preempt will imply a full memory barrier
		 */
		tsk->plug = plug;
	}
}
EXPORT_SYMBOL(blk_start_plug);

static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
{
	struct request *rqa = container_of(a, struct request, queuelist);
	struct request *rqb = container_of(b, struct request, queuelist);

	return !(rqa->q <= rqb->q);
}

/*
 * If 'from_schedule' is true, then postpone the dispatch of requests
 * until a safe kblockd context. We due this to avoid accidental big
 * additional stack usage in driver dispatch, in places where the originally
 * plugger did not intend it.
 */
static void queue_unplugged(struct request_queue *q, unsigned int depth,
			    bool from_schedule)
	__releases(q->queue_lock)
{
	trace_block_unplug(q, depth, !from_schedule);

	/*
	 * If we are punting this to kblockd, then we can safely drop
	 * the queue_lock before waking kblockd (which needs to take
	 * this lock).
	 */
	if (from_schedule) {
		spin_unlock(q->queue_lock);
		blk_run_queue_async(q);
	} else {
		__blk_run_queue(q);
		spin_unlock(q->queue_lock);
	}

}

static void flush_plug_callbacks(struct blk_plug *plug)
{
	LIST_HEAD(callbacks);

	if (list_empty(&plug->cb_list))
		return;

	list_splice_init(&plug->cb_list, &callbacks);

	while (!list_empty(&callbacks)) {
		struct blk_plug_cb *cb = list_first_entry(&callbacks,
							  struct blk_plug_cb,
							  list);
		list_del(&cb->list);
		cb->callback(cb);
	}
}

void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
{
	struct request_queue *q;
	unsigned long flags;
	struct request *rq;
	LIST_HEAD(list);
	unsigned int depth;

	BUG_ON(plug->magic != PLUG_MAGIC);

	flush_plug_callbacks(plug);
	if (list_empty(&plug->list))
		return;

	list_splice_init(&plug->list, &list);
	plug->count = 0;

	if (plug->should_sort) {
		list_sort(NULL, &list, plug_rq_cmp);
		plug->should_sort = 0;
	}

	q = NULL;
	depth = 0;

	/*
	 * Save and disable interrupts here, to avoid doing it for every
	 * queue lock we have to take.
	 */
	local_irq_save(flags);
	while (!list_empty(&list)) {
		rq = list_entry_rq(list.next);
		list_del_init(&rq->queuelist);
		BUG_ON(!rq->q);
		if (rq->q != q) {
			/*
			 * This drops the queue lock
			 */
			if (q)
				queue_unplugged(q, depth, from_schedule);
			q = rq->q;
			depth = 0;
			spin_lock(q->queue_lock);
		}
		/*
		 * rq is already accounted, so use raw insert
		 */
		if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA))
			__elv_add_request(q, rq, ELEVATOR_INSERT_FLUSH);
		else
			__elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);

		depth++;
	}

	/*
	 * This drops the queue lock
	 */
	if (q)
		queue_unplugged(q, depth, from_schedule);

	local_irq_restore(flags);
}

void blk_finish_plug(struct blk_plug *plug)
{
	blk_flush_plug_list(plug, false);

	if (plug == current->plug)
		current->plug = NULL;
}
EXPORT_SYMBOL(blk_finish_plug);

int __init blk_dev_init(void)
{
	BUILD_BUG_ON(__REQ_NR_BITS > 8 *
			sizeof(((struct request *)0)->cmd_flags));

	/* used for unplugging and affects IO latency/throughput - HIGHPRI */
	kblockd_workqueue = alloc_workqueue("kblockd",
					    WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
	if (!kblockd_workqueue)
		panic("Failed to create kblockd\n");

	request_cachep = kmem_cache_create("blkdev_requests",
			sizeof(struct request), 0, SLAB_PANIC, NULL);

	blk_requestq_cachep = kmem_cache_create("blkdev_queue",
			sizeof(struct request_queue), 0, SLAB_PANIC, NULL);

	return 0;
}