tnc_commit.c 26.8 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
/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Authors: Adrian Hunter
 *          Artem Bityutskiy (Битюцкий Артём)
 */

/* This file implements TNC functions for committing */

#include <linux/random.h>
#include "ubifs.h"

/**
 * make_idx_node - make an index node for fill-the-gaps method of TNC commit.
 * @c: UBIFS file-system description object
 * @idx: buffer in which to place new index node
 * @znode: znode from which to make new index node
 * @lnum: LEB number where new index node will be written
 * @offs: offset where new index node will be written
 * @len: length of new index node
 */
static int make_idx_node(struct ubifs_info *c, struct ubifs_idx_node *idx,
			 struct ubifs_znode *znode, int lnum, int offs, int len)
{
	struct ubifs_znode *zp;
	int i, err;

	/* Make index node */
	idx->ch.node_type = UBIFS_IDX_NODE;
	idx->child_cnt = cpu_to_le16(znode->child_cnt);
	idx->level = cpu_to_le16(znode->level);
	for (i = 0; i < znode->child_cnt; i++) {
		struct ubifs_branch *br = ubifs_idx_branch(c, idx, i);
		struct ubifs_zbranch *zbr = &znode->zbranch[i];

		key_write_idx(c, &zbr->key, &br->key);
		br->lnum = cpu_to_le32(zbr->lnum);
		br->offs = cpu_to_le32(zbr->offs);
		br->len = cpu_to_le32(zbr->len);
		if (!zbr->lnum || !zbr->len) {
			ubifs_err(c, "bad ref in znode");
			ubifs_dump_znode(c, znode);
			if (zbr->znode)
				ubifs_dump_znode(c, zbr->znode);
		}
	}
	ubifs_prepare_node(c, idx, len, 0);

	znode->lnum = lnum;
	znode->offs = offs;
	znode->len = len;

	err = insert_old_idx_znode(c, znode);

	/* Update the parent */
	zp = znode->parent;
	if (zp) {
		struct ubifs_zbranch *zbr;

		zbr = &zp->zbranch[znode->iip];
		zbr->lnum = lnum;
		zbr->offs = offs;
		zbr->len = len;
	} else {
		c->zroot.lnum = lnum;
		c->zroot.offs = offs;
		c->zroot.len = len;
	}
	c->calc_idx_sz += ALIGN(len, 8);

	atomic_long_dec(&c->dirty_zn_cnt);

	ubifs_assert(ubifs_zn_dirty(znode));
	ubifs_assert(ubifs_zn_cow(znode));

	/*
	 * Note, unlike 'write_index()' we do not add memory barriers here
	 * because this function is called with @c->tnc_mutex locked.
	 */
	__clear_bit(DIRTY_ZNODE, &znode->flags);
	__clear_bit(COW_ZNODE, &znode->flags);

	return err;
}

/**
 * fill_gap - make index nodes in gaps in dirty index LEBs.
 * @c: UBIFS file-system description object
 * @lnum: LEB number that gap appears in
 * @gap_start: offset of start of gap
 * @gap_end: offset of end of gap
 * @dirt: adds dirty space to this
 *
 * This function returns the number of index nodes written into the gap.
 */
static int fill_gap(struct ubifs_info *c, int lnum, int gap_start, int gap_end,
		    int *dirt)
{
	int len, gap_remains, gap_pos, written, pad_len;

	ubifs_assert((gap_start & 7) == 0);
	ubifs_assert((gap_end & 7) == 0);
	ubifs_assert(gap_end >= gap_start);

	gap_remains = gap_end - gap_start;
	if (!gap_remains)
		return 0;
	gap_pos = gap_start;
	written = 0;
	while (c->enext) {
		len = ubifs_idx_node_sz(c, c->enext->child_cnt);
		if (len < gap_remains) {
			struct ubifs_znode *znode = c->enext;
			const int alen = ALIGN(len, 8);
			int err;

			ubifs_assert(alen <= gap_remains);
			err = make_idx_node(c, c->ileb_buf + gap_pos, znode,
					    lnum, gap_pos, len);
			if (err)
				return err;
			gap_remains -= alen;
			gap_pos += alen;
			c->enext = znode->cnext;
			if (c->enext == c->cnext)
				c->enext = NULL;
			written += 1;
		} else
			break;
	}
	if (gap_end == c->leb_size) {
		c->ileb_len = ALIGN(gap_pos, c->min_io_size);
		/* Pad to end of min_io_size */
		pad_len = c->ileb_len - gap_pos;
	} else
		/* Pad to end of gap */
		pad_len = gap_remains;
	dbg_gc("LEB %d:%d to %d len %d nodes written %d wasted bytes %d",
	       lnum, gap_start, gap_end, gap_end - gap_start, written, pad_len);
	ubifs_pad(c, c->ileb_buf + gap_pos, pad_len);
	*dirt += pad_len;
	return written;
}

/**
 * find_old_idx - find an index node obsoleted since the last commit start.
 * @c: UBIFS file-system description object
 * @lnum: LEB number of obsoleted index node
 * @offs: offset of obsoleted index node
 *
 * Returns %1 if found and %0 otherwise.
 */
static int find_old_idx(struct ubifs_info *c, int lnum, int offs)
{
	struct ubifs_old_idx *o;
	struct rb_node *p;

	p = c->old_idx.rb_node;
	while (p) {
		o = rb_entry(p, struct ubifs_old_idx, rb);
		if (lnum < o->lnum)
			p = p->rb_left;
		else if (lnum > o->lnum)
			p = p->rb_right;
		else if (offs < o->offs)
			p = p->rb_left;
		else if (offs > o->offs)
			p = p->rb_right;
		else
			return 1;
	}
	return 0;
}

/**
 * is_idx_node_in_use - determine if an index node can be overwritten.
 * @c: UBIFS file-system description object
 * @key: key of index node
 * @level: index node level
 * @lnum: LEB number of index node
 * @offs: offset of index node
 *
 * If @key / @lnum / @offs identify an index node that was not part of the old
 * index, then this function returns %0 (obsolete).  Else if the index node was
 * part of the old index but is now dirty %1 is returned, else if it is clean %2
 * is returned. A negative error code is returned on failure.
 */
static int is_idx_node_in_use(struct ubifs_info *c, union ubifs_key *key,
			      int level, int lnum, int offs)
{
	int ret;

	ret = is_idx_node_in_tnc(c, key, level, lnum, offs);
	if (ret < 0)
		return ret; /* Error code */
	if (ret == 0)
		if (find_old_idx(c, lnum, offs))
			return 1;
	return ret;
}

/**
 * layout_leb_in_gaps - layout index nodes using in-the-gaps method.
 * @c: UBIFS file-system description object
 * @p: return LEB number here
 *
 * This function lays out new index nodes for dirty znodes using in-the-gaps
 * method of TNC commit.
 * This function merely puts the next znode into the next gap, making no attempt
 * to try to maximise the number of znodes that fit.
 * This function returns the number of index nodes written into the gaps, or a
 * negative error code on failure.
 */
static int layout_leb_in_gaps(struct ubifs_info *c, int *p)
{
	struct ubifs_scan_leb *sleb;
	struct ubifs_scan_node *snod;
	int lnum, dirt = 0, gap_start, gap_end, err, written, tot_written;

	tot_written = 0;
	/* Get an index LEB with lots of obsolete index nodes */
	lnum = ubifs_find_dirty_idx_leb(c);
	if (lnum < 0)
		/*
		 * There also may be dirt in the index head that could be
		 * filled, however we do not check there at present.
		 */
		return lnum; /* Error code */
	*p = lnum;
	dbg_gc("LEB %d", lnum);
	/*
	 * Scan the index LEB.  We use the generic scan for this even though
	 * it is more comprehensive and less efficient than is needed for this
	 * purpose.
	 */
	sleb = ubifs_scan(c, lnum, 0, c->ileb_buf, 0);
	c->ileb_len = 0;
	if (IS_ERR(sleb))
		return PTR_ERR(sleb);
	gap_start = 0;
	list_for_each_entry(snod, &sleb->nodes, list) {
		struct ubifs_idx_node *idx;
		int in_use, level;

		ubifs_assert(snod->type == UBIFS_IDX_NODE);
		idx = snod->node;
		key_read(c, ubifs_idx_key(c, idx), &snod->key);
		level = le16_to_cpu(idx->level);
		/* Determine if the index node is in use (not obsolete) */
		in_use = is_idx_node_in_use(c, &snod->key, level, lnum,
					    snod->offs);
		if (in_use < 0) {
			ubifs_scan_destroy(sleb);
			return in_use; /* Error code */
		}
		if (in_use) {
			if (in_use == 1)
				dirt += ALIGN(snod->len, 8);
			/*
			 * The obsolete index nodes form gaps that can be
			 * overwritten.  This gap has ended because we have
			 * found an index node that is still in use
			 * i.e. not obsolete
			 */
			gap_end = snod->offs;
			/* Try to fill gap */
			written = fill_gap(c, lnum, gap_start, gap_end, &dirt);
			if (written < 0) {
				ubifs_scan_destroy(sleb);
				return written; /* Error code */
			}
			tot_written += written;
			gap_start = ALIGN(snod->offs + snod->len, 8);
		}
	}
	ubifs_scan_destroy(sleb);
	c->ileb_len = c->leb_size;
	gap_end = c->leb_size;
	/* Try to fill gap */
	written = fill_gap(c, lnum, gap_start, gap_end, &dirt);
	if (written < 0)
		return written; /* Error code */
	tot_written += written;
	if (tot_written == 0) {
		struct ubifs_lprops lp;

		dbg_gc("LEB %d wrote %d index nodes", lnum, tot_written);
		err = ubifs_read_one_lp(c, lnum, &lp);
		if (err)
			return err;
		if (lp.free == c->leb_size) {
			/*
			 * We must have snatched this LEB from the idx_gc list
			 * so we need to correct the free and dirty space.
			 */
			err = ubifs_change_one_lp(c, lnum,
						  c->leb_size - c->ileb_len,
						  dirt, 0, 0, 0);
			if (err)
				return err;
		}
		return 0;
	}
	err = ubifs_change_one_lp(c, lnum, c->leb_size - c->ileb_len, dirt,
				  0, 0, 0);
	if (err)
		return err;
	err = ubifs_leb_change(c, lnum, c->ileb_buf, c->ileb_len);
	if (err)
		return err;
	dbg_gc("LEB %d wrote %d index nodes", lnum, tot_written);
	return tot_written;
}

/**
 * get_leb_cnt - calculate the number of empty LEBs needed to commit.
 * @c: UBIFS file-system description object
 * @cnt: number of znodes to commit
 *
 * This function returns the number of empty LEBs needed to commit @cnt znodes
 * to the current index head.  The number is not exact and may be more than
 * needed.
 */
static int get_leb_cnt(struct ubifs_info *c, int cnt)
{
	int d;

	/* Assume maximum index node size (i.e. overestimate space needed) */
	cnt -= (c->leb_size - c->ihead_offs) / c->max_idx_node_sz;
	if (cnt < 0)
		cnt = 0;
	d = c->leb_size / c->max_idx_node_sz;
	return DIV_ROUND_UP(cnt, d);
}

/**
 * layout_in_gaps - in-the-gaps method of committing TNC.
 * @c: UBIFS file-system description object
 * @cnt: number of dirty znodes to commit.
 *
 * This function lays out new index nodes for dirty znodes using in-the-gaps
 * method of TNC commit.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int layout_in_gaps(struct ubifs_info *c, int cnt)
{
	int err, leb_needed_cnt, written, *p;

	dbg_gc("%d znodes to write", cnt);

	c->gap_lebs = kmalloc(sizeof(int) * (c->lst.idx_lebs + 1), GFP_NOFS);
	if (!c->gap_lebs)
		return -ENOMEM;

	p = c->gap_lebs;
	do {
		ubifs_assert(p < c->gap_lebs + c->lst.idx_lebs);
		written = layout_leb_in_gaps(c, p);
		if (written < 0) {
			err = written;
			if (err != -ENOSPC) {
				kfree(c->gap_lebs);
				c->gap_lebs = NULL;
				return err;
			}
			if (!dbg_is_chk_index(c)) {
				/*
				 * Do not print scary warnings if the debugging
				 * option which forces in-the-gaps is enabled.
				 */
				ubifs_warn(c, "out of space");
				ubifs_dump_budg(c, &c->bi);
				ubifs_dump_lprops(c);
			}
			/* Try to commit anyway */
			break;
		}
		p++;
		cnt -= written;
		leb_needed_cnt = get_leb_cnt(c, cnt);
		dbg_gc("%d znodes remaining, need %d LEBs, have %d", cnt,
		       leb_needed_cnt, c->ileb_cnt);
	} while (leb_needed_cnt > c->ileb_cnt);

	*p = -1;
	return 0;
}

/**
 * layout_in_empty_space - layout index nodes in empty space.
 * @c: UBIFS file-system description object
 *
 * This function lays out new index nodes for dirty znodes using empty LEBs.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int layout_in_empty_space(struct ubifs_info *c)
{
	struct ubifs_znode *znode, *cnext, *zp;
	int lnum, offs, len, next_len, buf_len, buf_offs, used, avail;
	int wlen, blen, err;

	cnext = c->enext;
	if (!cnext)
		return 0;

	lnum = c->ihead_lnum;
	buf_offs = c->ihead_offs;

	buf_len = ubifs_idx_node_sz(c, c->fanout);
	buf_len = ALIGN(buf_len, c->min_io_size);
	used = 0;
	avail = buf_len;

	/* Ensure there is enough room for first write */
	next_len = ubifs_idx_node_sz(c, cnext->child_cnt);
	if (buf_offs + next_len > c->leb_size)
		lnum = -1;

	while (1) {
		znode = cnext;

		len = ubifs_idx_node_sz(c, znode->child_cnt);

		/* Determine the index node position */
		if (lnum == -1) {
			if (c->ileb_nxt >= c->ileb_cnt) {
				ubifs_err(c, "out of space");
				return -ENOSPC;
			}
			lnum = c->ilebs[c->ileb_nxt++];
			buf_offs = 0;
			used = 0;
			avail = buf_len;
		}

		offs = buf_offs + used;

		znode->lnum = lnum;
		znode->offs = offs;
		znode->len = len;

		/* Update the parent */
		zp = znode->parent;
		if (zp) {
			struct ubifs_zbranch *zbr;
			int i;

			i = znode->iip;
			zbr = &zp->zbranch[i];
			zbr->lnum = lnum;
			zbr->offs = offs;
			zbr->len = len;
		} else {
			c->zroot.lnum = lnum;
			c->zroot.offs = offs;
			c->zroot.len = len;
		}
		c->calc_idx_sz += ALIGN(len, 8);

		/*
		 * Once lprops is updated, we can decrease the dirty znode count
		 * but it is easier to just do it here.
		 */
		atomic_long_dec(&c->dirty_zn_cnt);

		/*
		 * Calculate the next index node length to see if there is
		 * enough room for it
		 */
		cnext = znode->cnext;
		if (cnext == c->cnext)
			next_len = 0;
		else
			next_len = ubifs_idx_node_sz(c, cnext->child_cnt);

		/* Update buffer positions */
		wlen = used + len;
		used += ALIGN(len, 8);
		avail -= ALIGN(len, 8);

		if (next_len != 0 &&
		    buf_offs + used + next_len <= c->leb_size &&
		    avail > 0)
			continue;

		if (avail <= 0 && next_len &&
		    buf_offs + used + next_len <= c->leb_size)
			blen = buf_len;
		else
			blen = ALIGN(wlen, c->min_io_size);

		/* The buffer is full or there are no more znodes to do */
		buf_offs += blen;
		if (next_len) {
			if (buf_offs + next_len > c->leb_size) {
				err = ubifs_update_one_lp(c, lnum,
					c->leb_size - buf_offs, blen - used,
					0, 0);
				if (err)
					return err;
				lnum = -1;
			}
			used -= blen;
			if (used < 0)
				used = 0;
			avail = buf_len - used;
			continue;
		}
		err = ubifs_update_one_lp(c, lnum, c->leb_size - buf_offs,
					  blen - used, 0, 0);
		if (err)
			return err;
		break;
	}

	c->dbg->new_ihead_lnum = lnum;
	c->dbg->new_ihead_offs = buf_offs;

	return 0;
}

/**
 * layout_commit - determine positions of index nodes to commit.
 * @c: UBIFS file-system description object
 * @no_space: indicates that insufficient empty LEBs were allocated
 * @cnt: number of znodes to commit
 *
 * Calculate and update the positions of index nodes to commit.  If there were
 * an insufficient number of empty LEBs allocated, then index nodes are placed
 * into the gaps created by obsolete index nodes in non-empty index LEBs.  For
 * this purpose, an obsolete index node is one that was not in the index as at
 * the end of the last commit.  To write "in-the-gaps" requires that those index
 * LEBs are updated atomically in-place.
 */
static int layout_commit(struct ubifs_info *c, int no_space, int cnt)
{
	int err;

	if (no_space) {
		err = layout_in_gaps(c, cnt);
		if (err)
			return err;
	}
	err = layout_in_empty_space(c);
	return err;
}

/**
 * find_first_dirty - find first dirty znode.
 * @znode: znode to begin searching from
 */
static struct ubifs_znode *find_first_dirty(struct ubifs_znode *znode)
{
	int i, cont;

	if (!znode)
		return NULL;

	while (1) {
		if (znode->level == 0) {
			if (ubifs_zn_dirty(znode))
				return znode;
			return NULL;
		}
		cont = 0;
		for (i = 0; i < znode->child_cnt; i++) {
			struct ubifs_zbranch *zbr = &znode->zbranch[i];

			if (zbr->znode && ubifs_zn_dirty(zbr->znode)) {
				znode = zbr->znode;
				cont = 1;
				break;
			}
		}
		if (!cont) {
			if (ubifs_zn_dirty(znode))
				return znode;
			return NULL;
		}
	}
}

/**
 * find_next_dirty - find next dirty znode.
 * @znode: znode to begin searching from
 */
static struct ubifs_znode *find_next_dirty(struct ubifs_znode *znode)
{
	int n = znode->iip + 1;

	znode = znode->parent;
	if (!znode)
		return NULL;
	for (; n < znode->child_cnt; n++) {
		struct ubifs_zbranch *zbr = &znode->zbranch[n];

		if (zbr->znode && ubifs_zn_dirty(zbr->znode))
			return find_first_dirty(zbr->znode);
	}
	return znode;
}

/**
 * get_znodes_to_commit - create list of dirty znodes to commit.
 * @c: UBIFS file-system description object
 *
 * This function returns the number of znodes to commit.
 */
static int get_znodes_to_commit(struct ubifs_info *c)
{
	struct ubifs_znode *znode, *cnext;
	int cnt = 0;

	c->cnext = find_first_dirty(c->zroot.znode);
	znode = c->enext = c->cnext;
	if (!znode) {
		dbg_cmt("no znodes to commit");
		return 0;
	}
	cnt += 1;
	while (1) {
		ubifs_assert(!ubifs_zn_cow(znode));
		__set_bit(COW_ZNODE, &znode->flags);
		znode->alt = 0;
		cnext = find_next_dirty(znode);
		if (!cnext) {
			znode->cnext = c->cnext;
			break;
		}
		znode->cnext = cnext;
		znode = cnext;
		cnt += 1;
	}
	dbg_cmt("committing %d znodes", cnt);
	ubifs_assert(cnt == atomic_long_read(&c->dirty_zn_cnt));
	return cnt;
}

/**
 * alloc_idx_lebs - allocate empty LEBs to be used to commit.
 * @c: UBIFS file-system description object
 * @cnt: number of znodes to commit
 *
 * This function returns %-ENOSPC if it cannot allocate a sufficient number of
 * empty LEBs.  %0 is returned on success, otherwise a negative error code
 * is returned.
 */
static int alloc_idx_lebs(struct ubifs_info *c, int cnt)
{
	int i, leb_cnt, lnum;

	c->ileb_cnt = 0;
	c->ileb_nxt = 0;
	leb_cnt = get_leb_cnt(c, cnt);
	dbg_cmt("need about %d empty LEBS for TNC commit", leb_cnt);
	if (!leb_cnt)
		return 0;
	c->ilebs = kmalloc(leb_cnt * sizeof(int), GFP_NOFS);
	if (!c->ilebs)
		return -ENOMEM;
	for (i = 0; i < leb_cnt; i++) {
		lnum = ubifs_find_free_leb_for_idx(c);
		if (lnum < 0)
			return lnum;
		c->ilebs[c->ileb_cnt++] = lnum;
		dbg_cmt("LEB %d", lnum);
	}
	if (dbg_is_chk_index(c) && !(prandom_u32() & 7))
		return -ENOSPC;
	return 0;
}

/**
 * free_unused_idx_lebs - free unused LEBs that were allocated for the commit.
 * @c: UBIFS file-system description object
 *
 * It is possible that we allocate more empty LEBs for the commit than we need.
 * This functions frees the surplus.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int free_unused_idx_lebs(struct ubifs_info *c)
{
	int i, err = 0, lnum, er;

	for (i = c->ileb_nxt; i < c->ileb_cnt; i++) {
		lnum = c->ilebs[i];
		dbg_cmt("LEB %d", lnum);
		er = ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
					 LPROPS_INDEX | LPROPS_TAKEN, 0);
		if (!err)
			err = er;
	}
	return err;
}

/**
 * free_idx_lebs - free unused LEBs after commit end.
 * @c: UBIFS file-system description object
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int free_idx_lebs(struct ubifs_info *c)
{
	int err;

	err = free_unused_idx_lebs(c);
	kfree(c->ilebs);
	c->ilebs = NULL;
	return err;
}

/**
 * ubifs_tnc_start_commit - start TNC commit.
 * @c: UBIFS file-system description object
 * @zroot: new index root position is returned here
 *
 * This function prepares the list of indexing nodes to commit and lays out
 * their positions on flash. If there is not enough free space it uses the
 * in-gap commit method. Returns zero in case of success and a negative error
 * code in case of failure.
 */
int ubifs_tnc_start_commit(struct ubifs_info *c, struct ubifs_zbranch *zroot)
{
	int err = 0, cnt;

	mutex_lock(&c->tnc_mutex);
	err = dbg_check_tnc(c, 1);
	if (err)
		goto out;
	cnt = get_znodes_to_commit(c);
	if (cnt != 0) {
		int no_space = 0;

		err = alloc_idx_lebs(c, cnt);
		if (err == -ENOSPC)
			no_space = 1;
		else if (err)
			goto out_free;
		err = layout_commit(c, no_space, cnt);
		if (err)
			goto out_free;
		ubifs_assert(atomic_long_read(&c->dirty_zn_cnt) == 0);
		err = free_unused_idx_lebs(c);
		if (err)
			goto out;
	}
	destroy_old_idx(c);
	memcpy(zroot, &c->zroot, sizeof(struct ubifs_zbranch));

	err = ubifs_save_dirty_idx_lnums(c);
	if (err)
		goto out;

	spin_lock(&c->space_lock);
	/*
	 * Although we have not finished committing yet, update size of the
	 * committed index ('c->bi.old_idx_sz') and zero out the index growth
	 * budget. It is OK to do this now, because we've reserved all the
	 * space which is needed to commit the index, and it is save for the
	 * budgeting subsystem to assume the index is already committed,
	 * even though it is not.
	 */
	ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
	c->bi.old_idx_sz = c->calc_idx_sz;
	c->bi.uncommitted_idx = 0;
	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
	spin_unlock(&c->space_lock);
	mutex_unlock(&c->tnc_mutex);

	dbg_cmt("number of index LEBs %d", c->lst.idx_lebs);
	dbg_cmt("size of index %llu", c->calc_idx_sz);
	return err;

out_free:
	free_idx_lebs(c);
out:
	mutex_unlock(&c->tnc_mutex);
	return err;
}

/**
 * write_index - write index nodes.
 * @c: UBIFS file-system description object
 *
 * This function writes the index nodes whose positions were laid out in the
 * layout_in_empty_space function.
 */
static int write_index(struct ubifs_info *c)
{
	struct ubifs_idx_node *idx;
	struct ubifs_znode *znode, *cnext;
	int i, lnum, offs, len, next_len, buf_len, buf_offs, used;
	int avail, wlen, err, lnum_pos = 0, blen, nxt_offs;

	cnext = c->enext;
	if (!cnext)
		return 0;

	/*
	 * Always write index nodes to the index head so that index nodes and
	 * other types of nodes are never mixed in the same erase block.
	 */
	lnum = c->ihead_lnum;
	buf_offs = c->ihead_offs;

	/* Allocate commit buffer */
	buf_len = ALIGN(c->max_idx_node_sz, c->min_io_size);
	used = 0;
	avail = buf_len;

	/* Ensure there is enough room for first write */
	next_len = ubifs_idx_node_sz(c, cnext->child_cnt);
	if (buf_offs + next_len > c->leb_size) {
		err = ubifs_update_one_lp(c, lnum, LPROPS_NC, 0, 0,
					  LPROPS_TAKEN);
		if (err)
			return err;
		lnum = -1;
	}

	while (1) {
		cond_resched();

		znode = cnext;
		idx = c->cbuf + used;

		/* Make index node */
		idx->ch.node_type = UBIFS_IDX_NODE;
		idx->child_cnt = cpu_to_le16(znode->child_cnt);
		idx->level = cpu_to_le16(znode->level);
		for (i = 0; i < znode->child_cnt; i++) {
			struct ubifs_branch *br = ubifs_idx_branch(c, idx, i);
			struct ubifs_zbranch *zbr = &znode->zbranch[i];

			key_write_idx(c, &zbr->key, &br->key);
			br->lnum = cpu_to_le32(zbr->lnum);
			br->offs = cpu_to_le32(zbr->offs);
			br->len = cpu_to_le32(zbr->len);
			if (!zbr->lnum || !zbr->len) {
				ubifs_err(c, "bad ref in znode");
				ubifs_dump_znode(c, znode);
				if (zbr->znode)
					ubifs_dump_znode(c, zbr->znode);
			}
		}
		len = ubifs_idx_node_sz(c, znode->child_cnt);
		ubifs_prepare_node(c, idx, len, 0);

		/* Determine the index node position */
		if (lnum == -1) {
			lnum = c->ilebs[lnum_pos++];
			buf_offs = 0;
			used = 0;
			avail = buf_len;
		}
		offs = buf_offs + used;

		if (lnum != znode->lnum || offs != znode->offs ||
		    len != znode->len) {
			ubifs_err(c, "inconsistent znode posn");
			return -EINVAL;
		}

		/* Grab some stuff from znode while we still can */
		cnext = znode->cnext;

		ubifs_assert(ubifs_zn_dirty(znode));
		ubifs_assert(ubifs_zn_cow(znode));

		/*
		 * It is important that other threads should see %DIRTY_ZNODE
		 * flag cleared before %COW_ZNODE. Specifically, it matters in
		 * the 'dirty_cow_znode()' function. This is the reason for the
		 * first barrier. Also, we want the bit changes to be seen to
		 * other threads ASAP, to avoid unnecesarry copying, which is
		 * the reason for the second barrier.
		 */
		clear_bit(DIRTY_ZNODE, &znode->flags);
		smp_mb__before_atomic();
		clear_bit(COW_ZNODE, &znode->flags);
		smp_mb__after_atomic();

		/*
		 * We have marked the znode as clean but have not updated the
		 * @c->clean_zn_cnt counter. If this znode becomes dirty again
		 * before 'free_obsolete_znodes()' is called, then
		 * @c->clean_zn_cnt will be decremented before it gets
		 * incremented (resulting in 2 decrements for the same znode).
		 * This means that @c->clean_zn_cnt may become negative for a
		 * while.
		 *
		 * Q: why we cannot increment @c->clean_zn_cnt?
		 * A: because we do not have the @c->tnc_mutex locked, and the
		 *    following code would be racy and buggy:
		 *
		 *    if (!ubifs_zn_obsolete(znode)) {
		 *            atomic_long_inc(&c->clean_zn_cnt);
		 *            atomic_long_inc(&ubifs_clean_zn_cnt);
		 *    }
		 *
		 *    Thus, we just delay the @c->clean_zn_cnt update until we
		 *    have the mutex locked.
		 */

		/* Do not access znode from this point on */

		/* Update buffer positions */
		wlen = used + len;
		used += ALIGN(len, 8);
		avail -= ALIGN(len, 8);

		/*
		 * Calculate the next index node length to see if there is
		 * enough room for it
		 */
		if (cnext == c->cnext)
			next_len = 0;
		else
			next_len = ubifs_idx_node_sz(c, cnext->child_cnt);

		nxt_offs = buf_offs + used + next_len;
		if (next_len && nxt_offs <= c->leb_size) {
			if (avail > 0)
				continue;
			else
				blen = buf_len;
		} else {
			wlen = ALIGN(wlen, 8);
			blen = ALIGN(wlen, c->min_io_size);
			ubifs_pad(c, c->cbuf + wlen, blen - wlen);
		}

		/* The buffer is full or there are no more znodes to do */
		err = ubifs_leb_write(c, lnum, c->cbuf, buf_offs, blen);
		if (err)
			return err;
		buf_offs += blen;
		if (next_len) {
			if (nxt_offs > c->leb_size) {
				err = ubifs_update_one_lp(c, lnum, LPROPS_NC, 0,
							  0, LPROPS_TAKEN);
				if (err)
					return err;
				lnum = -1;
			}
			used -= blen;
			if (used < 0)
				used = 0;
			avail = buf_len - used;
			memmove(c->cbuf, c->cbuf + blen, used);
			continue;
		}
		break;
	}

	if (lnum != c->dbg->new_ihead_lnum ||
	    buf_offs != c->dbg->new_ihead_offs) {
		ubifs_err(c, "inconsistent ihead");
		return -EINVAL;
	}

	c->ihead_lnum = lnum;
	c->ihead_offs = buf_offs;

	return 0;
}

/**
 * free_obsolete_znodes - free obsolete znodes.
 * @c: UBIFS file-system description object
 *
 * At the end of commit end, obsolete znodes are freed.
 */
static void free_obsolete_znodes(struct ubifs_info *c)
{
	struct ubifs_znode *znode, *cnext;

	cnext = c->cnext;
	do {
		znode = cnext;
		cnext = znode->cnext;
		if (ubifs_zn_obsolete(znode))
			kfree(znode);
		else {
			znode->cnext = NULL;
			atomic_long_inc(&c->clean_zn_cnt);
			atomic_long_inc(&ubifs_clean_zn_cnt);
		}
	} while (cnext != c->cnext);
}

/**
 * return_gap_lebs - return LEBs used by the in-gap commit method.
 * @c: UBIFS file-system description object
 *
 * This function clears the "taken" flag for the LEBs which were used by the
 * "commit in-the-gaps" method.
 */
static int return_gap_lebs(struct ubifs_info *c)
{
	int *p, err;

	if (!c->gap_lebs)
		return 0;

	dbg_cmt("");
	for (p = c->gap_lebs; *p != -1; p++) {
		err = ubifs_change_one_lp(c, *p, LPROPS_NC, LPROPS_NC, 0,
					  LPROPS_TAKEN, 0);
		if (err)
			return err;
	}

	kfree(c->gap_lebs);
	c->gap_lebs = NULL;
	return 0;
}

/**
 * ubifs_tnc_end_commit - update the TNC for commit end.
 * @c: UBIFS file-system description object
 *
 * Write the dirty znodes.
 */
int ubifs_tnc_end_commit(struct ubifs_info *c)
{
	int err;

	if (!c->cnext)
		return 0;

	err = return_gap_lebs(c);
	if (err)
		return err;

	err = write_index(c);
	if (err)
		return err;

	mutex_lock(&c->tnc_mutex);

	dbg_cmt("TNC height is %d", c->zroot.znode->level + 1);

	free_obsolete_znodes(c);

	c->cnext = NULL;
	kfree(c->ilebs);
	c->ilebs = NULL;

	mutex_unlock(&c->tnc_mutex);

	return 0;
}