budget.c 23.8 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
/*
 * 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 the budgeting sub-system which is responsible for UBIFS
 * space management.
 *
 * Factors such as compression, wasted space at the ends of LEBs, space in other
 * journal heads, the effect of updates on the index, and so on, make it
 * impossible to accurately predict the amount of space needed. Consequently
 * approximations are used.
 */

#include "ubifs.h"
#include <linux/writeback.h>
#include <linux/math64.h>

/*
 * When pessimistic budget calculations say that there is no enough space,
 * UBIFS starts writing back dirty inodes and pages, doing garbage collection,
 * or committing. The below constant defines maximum number of times UBIFS
 * repeats the operations.
 */
#define MAX_MKSPC_RETRIES 3

/*
 * The below constant defines amount of dirty pages which should be written
 * back at when trying to shrink the liability.
 */
#define NR_TO_WRITE 16

/**
 * shrink_liability - write-back some dirty pages/inodes.
 * @c: UBIFS file-system description object
 * @nr_to_write: how many dirty pages to write-back
 *
 * This function shrinks UBIFS liability by means of writing back some amount
 * of dirty inodes and their pages.
 *
 * Note, this function synchronizes even VFS inodes which are locked
 * (@i_mutex) by the caller of the budgeting function, because write-back does
 * not touch @i_mutex.
 */
static void shrink_liability(struct ubifs_info *c, int nr_to_write)
{
	down_read(&c->vfs_sb->s_umount);
	writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);
	up_read(&c->vfs_sb->s_umount);
}

/**
 * run_gc - run garbage collector.
 * @c: UBIFS file-system description object
 *
 * This function runs garbage collector to make some more free space. Returns
 * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a
 * negative error code in case of failure.
 */
static int run_gc(struct ubifs_info *c)
{
	int err, lnum;

	/* Make some free space by garbage-collecting dirty space */
	down_read(&c->commit_sem);
	lnum = ubifs_garbage_collect(c, 1);
	up_read(&c->commit_sem);
	if (lnum < 0)
		return lnum;

	/* GC freed one LEB, return it to lprops */
	dbg_budg("GC freed LEB %d", lnum);
	err = ubifs_return_leb(c, lnum);
	if (err)
		return err;
	return 0;
}

/**
 * get_liability - calculate current liability.
 * @c: UBIFS file-system description object
 *
 * This function calculates and returns current UBIFS liability, i.e. the
 * amount of bytes UBIFS has "promised" to write to the media.
 */
static long long get_liability(struct ubifs_info *c)
{
	long long liab;

	spin_lock(&c->space_lock);
	liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;
	spin_unlock(&c->space_lock);
	return liab;
}

/**
 * make_free_space - make more free space on the file-system.
 * @c: UBIFS file-system description object
 *
 * This function is called when an operation cannot be budgeted because there
 * is supposedly no free space. But in most cases there is some free space:
 *   o budgeting is pessimistic, so it always budgets more than it is actually
 *     needed, so shrinking the liability is one way to make free space - the
 *     cached data will take less space then it was budgeted for;
 *   o GC may turn some dark space into free space (budgeting treats dark space
 *     as not available);
 *   o commit may free some LEB, i.e., turn freeable LEBs into free LEBs.
 *
 * So this function tries to do the above. Returns %-EAGAIN if some free space
 * was presumably made and the caller has to re-try budgeting the operation.
 * Returns %-ENOSPC if it couldn't do more free space, and other negative error
 * codes on failures.
 */
static int make_free_space(struct ubifs_info *c)
{
	int err, retries = 0;
	long long liab1, liab2;

	do {
		liab1 = get_liability(c);
		/*
		 * We probably have some dirty pages or inodes (liability), try
		 * to write them back.
		 */
		dbg_budg("liability %lld, run write-back", liab1);
		shrink_liability(c, NR_TO_WRITE);

		liab2 = get_liability(c);
		if (liab2 < liab1)
			return -EAGAIN;

		dbg_budg("new liability %lld (not shrunk)", liab2);

		/* Liability did not shrink again, try GC */
		dbg_budg("Run GC");
		err = run_gc(c);
		if (!err)
			return -EAGAIN;

		if (err != -EAGAIN && err != -ENOSPC)
			/* Some real error happened */
			return err;

		dbg_budg("Run commit (retries %d)", retries);
		err = ubifs_run_commit(c);
		if (err)
			return err;
	} while (retries++ < MAX_MKSPC_RETRIES);

	return -ENOSPC;
}

/**
 * ubifs_calc_min_idx_lebs - calculate amount of LEBs for the index.
 * @c: UBIFS file-system description object
 *
 * This function calculates and returns the number of LEBs which should be kept
 * for index usage.
 */
int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
{
	int idx_lebs;
	long long idx_size;

	idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;
	/* And make sure we have thrice the index size of space reserved */
	idx_size += idx_size << 1;
	/*
	 * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
	 * pair, nor similarly the two variables for the new index size, so we
	 * have to do this costly 64-bit division on fast-path.
	 */
	idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);
	/*
	 * The index head is not available for the in-the-gaps method, so add an
	 * extra LEB to compensate.
	 */
	idx_lebs += 1;
	if (idx_lebs < MIN_INDEX_LEBS)
		idx_lebs = MIN_INDEX_LEBS;
	return idx_lebs;
}

/**
 * ubifs_calc_available - calculate available FS space.
 * @c: UBIFS file-system description object
 * @min_idx_lebs: minimum number of LEBs reserved for the index
 *
 * This function calculates and returns amount of FS space available for use.
 */
long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
{
	int subtract_lebs;
	long long available;

	available = c->main_bytes - c->lst.total_used;

	/*
	 * Now 'available' contains theoretically available flash space
	 * assuming there is no index, so we have to subtract the space which
	 * is reserved for the index.
	 */
	subtract_lebs = min_idx_lebs;

	/* Take into account that GC reserves one LEB for its own needs */
	subtract_lebs += 1;

	/*
	 * The GC journal head LEB is not really accessible. And since
	 * different write types go to different heads, we may count only on
	 * one head's space.
	 */
	subtract_lebs += c->jhead_cnt - 1;

	/* We also reserve one LEB for deletions, which bypass budgeting */
	subtract_lebs += 1;

	available -= (long long)subtract_lebs * c->leb_size;

	/* Subtract the dead space which is not available for use */
	available -= c->lst.total_dead;

	/*
	 * Subtract dark space, which might or might not be usable - it depends
	 * on the data which we have on the media and which will be written. If
	 * this is a lot of uncompressed or not-compressible data, the dark
	 * space cannot be used.
	 */
	available -= c->lst.total_dark;

	/*
	 * However, there is more dark space. The index may be bigger than
	 * @min_idx_lebs. Those extra LEBs are assumed to be available, but
	 * their dark space is not included in total_dark, so it is subtracted
	 * here.
	 */
	if (c->lst.idx_lebs > min_idx_lebs) {
		subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
		available -= subtract_lebs * c->dark_wm;
	}

	/* The calculations are rough and may end up with a negative number */
	return available > 0 ? available : 0;
}

/**
 * can_use_rp - check whether the user is allowed to use reserved pool.
 * @c: UBIFS file-system description object
 *
 * UBIFS has so-called "reserved pool" which is flash space reserved
 * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock.
 * This function checks whether current user is allowed to use reserved pool.
 * Returns %1  current user is allowed to use reserved pool and %0 otherwise.
 */
static int can_use_rp(struct ubifs_info *c)
{
	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
		return 1;
	return 0;
}

/**
 * do_budget_space - reserve flash space for index and data growth.
 * @c: UBIFS file-system description object
 *
 * This function makes sure UBIFS has enough free LEBs for index growth and
 * data.
 *
 * When budgeting index space, UBIFS reserves thrice as many LEBs as the index
 * would take if it was consolidated and written to the flash. This guarantees
 * that the "in-the-gaps" commit method always succeeds and UBIFS will always
 * be able to commit dirty index. So this function basically adds amount of
 * budgeted index space to the size of the current index, multiplies this by 3,
 * and makes sure this does not exceed the amount of free LEBs.
 *
 * Notes about @c->bi.min_idx_lebs and @c->lst.idx_lebs variables:
 * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might
 *    be large, because UBIFS does not do any index consolidation as long as
 *    there is free space. IOW, the index may take a lot of LEBs, but the LEBs
 *    will contain a lot of dirt.
 * o @c->bi.min_idx_lebs is the number of LEBS the index presumably takes. IOW,
 *    the index may be consolidated to take up to @c->bi.min_idx_lebs LEBs.
 *
 * This function returns zero in case of success, and %-ENOSPC in case of
 * failure.
 */
static int do_budget_space(struct ubifs_info *c)
{
	long long outstanding, available;
	int lebs, rsvd_idx_lebs, min_idx_lebs;

	/* First budget index space */
	min_idx_lebs = ubifs_calc_min_idx_lebs(c);

	/* Now 'min_idx_lebs' contains number of LEBs to reserve */
	if (min_idx_lebs > c->lst.idx_lebs)
		rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
	else
		rsvd_idx_lebs = 0;

	/*
	 * The number of LEBs that are available to be used by the index is:
	 *
	 *    @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
	 *    @c->lst.taken_empty_lebs
	 *
	 * @c->lst.empty_lebs are available because they are empty.
	 * @c->freeable_cnt are available because they contain only free and
	 * dirty space, @c->idx_gc_cnt are available because they are index
	 * LEBs that have been garbage collected and are awaiting the commit
	 * before they can be used. And the in-the-gaps method will grab these
	 * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
	 * already been allocated for some purpose.
	 *
	 * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
	 * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
	 * are taken until after the commit).
	 *
	 * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
	 * because of the way we serialize LEB allocations and budgeting. See a
	 * comment in 'ubifs_find_free_space()'.
	 */
	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
	       c->lst.taken_empty_lebs;
	if (unlikely(rsvd_idx_lebs > lebs)) {
		dbg_budg("out of indexing space: min_idx_lebs %d (old %d), rsvd_idx_lebs %d",
			 min_idx_lebs, c->bi.min_idx_lebs, rsvd_idx_lebs);
		return -ENOSPC;
	}

	available = ubifs_calc_available(c, min_idx_lebs);
	outstanding = c->bi.data_growth + c->bi.dd_growth;

	if (unlikely(available < outstanding)) {
		dbg_budg("out of data space: available %lld, outstanding %lld",
			 available, outstanding);
		return -ENOSPC;
	}

	if (available - outstanding <= c->rp_size && !can_use_rp(c))
		return -ENOSPC;

	c->bi.min_idx_lebs = min_idx_lebs;
	return 0;
}

/**
 * calc_idx_growth - calculate approximate index growth from budgeting request.
 * @c: UBIFS file-system description object
 * @req: budgeting request
 *
 * For now we assume each new node adds one znode. But this is rather poor
 * approximation, though.
 */
static int calc_idx_growth(const struct ubifs_info *c,
			   const struct ubifs_budget_req *req)
{
	int znodes;

	znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
		 req->new_dent;
	return znodes * c->max_idx_node_sz;
}

/**
 * calc_data_growth - calculate approximate amount of new data from budgeting
 * request.
 * @c: UBIFS file-system description object
 * @req: budgeting request
 */
static int calc_data_growth(const struct ubifs_info *c,
			    const struct ubifs_budget_req *req)
{
	int data_growth;

	data_growth = req->new_ino  ? c->bi.inode_budget : 0;
	if (req->new_page)
		data_growth += c->bi.page_budget;
	if (req->new_dent)
		data_growth += c->bi.dent_budget;
	data_growth += req->new_ino_d;
	return data_growth;
}

/**
 * calc_dd_growth - calculate approximate amount of data which makes other data
 * dirty from budgeting request.
 * @c: UBIFS file-system description object
 * @req: budgeting request
 */
static int calc_dd_growth(const struct ubifs_info *c,
			  const struct ubifs_budget_req *req)
{
	int dd_growth;

	dd_growth = req->dirtied_page ? c->bi.page_budget : 0;

	if (req->dirtied_ino)
		dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);
	if (req->mod_dent)
		dd_growth += c->bi.dent_budget;
	dd_growth += req->dirtied_ino_d;
	return dd_growth;
}

/**
 * ubifs_budget_space - ensure there is enough space to complete an operation.
 * @c: UBIFS file-system description object
 * @req: budget request
 *
 * This function allocates budget for an operation. It uses pessimistic
 * approximation of how much flash space the operation needs. The goal of this
 * function is to make sure UBIFS always has flash space to flush all dirty
 * pages, dirty inodes, and dirty znodes (liability). This function may force
 * commit, garbage-collection or write-back. Returns zero in case of success,
 * %-ENOSPC if there is no free space and other negative error codes in case of
 * failures.
 */
int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
{
	int err, idx_growth, data_growth, dd_growth, retried = 0;

	ubifs_assert(req->new_page <= 1);
	ubifs_assert(req->dirtied_page <= 1);
	ubifs_assert(req->new_dent <= 1);
	ubifs_assert(req->mod_dent <= 1);
	ubifs_assert(req->new_ino <= 1);
	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
	ubifs_assert(req->dirtied_ino <= 4);
	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
	ubifs_assert(!(req->new_ino_d & 7));
	ubifs_assert(!(req->dirtied_ino_d & 7));

	data_growth = calc_data_growth(c, req);
	dd_growth = calc_dd_growth(c, req);
	if (!data_growth && !dd_growth)
		return 0;
	idx_growth = calc_idx_growth(c, req);

again:
	spin_lock(&c->space_lock);
	ubifs_assert(c->bi.idx_growth >= 0);
	ubifs_assert(c->bi.data_growth >= 0);
	ubifs_assert(c->bi.dd_growth >= 0);

	if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {
		dbg_budg("no space");
		spin_unlock(&c->space_lock);
		return -ENOSPC;
	}

	c->bi.idx_growth += idx_growth;
	c->bi.data_growth += data_growth;
	c->bi.dd_growth += dd_growth;

	err = do_budget_space(c);
	if (likely(!err)) {
		req->idx_growth = idx_growth;
		req->data_growth = data_growth;
		req->dd_growth = dd_growth;
		spin_unlock(&c->space_lock);
		return 0;
	}

	/* Restore the old values */
	c->bi.idx_growth -= idx_growth;
	c->bi.data_growth -= data_growth;
	c->bi.dd_growth -= dd_growth;
	spin_unlock(&c->space_lock);

	if (req->fast) {
		dbg_budg("no space for fast budgeting");
		return err;
	}

	err = make_free_space(c);
	cond_resched();
	if (err == -EAGAIN) {
		dbg_budg("try again");
		goto again;
	} else if (err == -ENOSPC) {
		if (!retried) {
			retried = 1;
			dbg_budg("-ENOSPC, but anyway try once again");
			goto again;
		}
		dbg_budg("FS is full, -ENOSPC");
		c->bi.nospace = 1;
		if (can_use_rp(c) || c->rp_size == 0)
			c->bi.nospace_rp = 1;
		smp_wmb();
	} else
		ubifs_err(c, "cannot budget space, error %d", err);
	return err;
}

/**
 * ubifs_release_budget - release budgeted free space.
 * @c: UBIFS file-system description object
 * @req: budget request
 *
 * This function releases the space budgeted by 'ubifs_budget_space()'. Note,
 * since the index changes (which were budgeted for in @req->idx_growth) will
 * only be written to the media on commit, this function moves the index budget
 * from @c->bi.idx_growth to @c->bi.uncommitted_idx. The latter will be zeroed
 * by the commit operation.
 */
void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
{
	ubifs_assert(req->new_page <= 1);
	ubifs_assert(req->dirtied_page <= 1);
	ubifs_assert(req->new_dent <= 1);
	ubifs_assert(req->mod_dent <= 1);
	ubifs_assert(req->new_ino <= 1);
	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
	ubifs_assert(req->dirtied_ino <= 4);
	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
	ubifs_assert(!(req->new_ino_d & 7));
	ubifs_assert(!(req->dirtied_ino_d & 7));
	if (!req->recalculate) {
		ubifs_assert(req->idx_growth >= 0);
		ubifs_assert(req->data_growth >= 0);
		ubifs_assert(req->dd_growth >= 0);
	}

	if (req->recalculate) {
		req->data_growth = calc_data_growth(c, req);
		req->dd_growth = calc_dd_growth(c, req);
		req->idx_growth = calc_idx_growth(c, req);
	}

	if (!req->data_growth && !req->dd_growth)
		return;

	c->bi.nospace = c->bi.nospace_rp = 0;
	smp_wmb();

	spin_lock(&c->space_lock);
	c->bi.idx_growth -= req->idx_growth;
	c->bi.uncommitted_idx += req->idx_growth;
	c->bi.data_growth -= req->data_growth;
	c->bi.dd_growth -= req->dd_growth;
	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);

	ubifs_assert(c->bi.idx_growth >= 0);
	ubifs_assert(c->bi.data_growth >= 0);
	ubifs_assert(c->bi.dd_growth >= 0);
	ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
	ubifs_assert(!(c->bi.idx_growth & 7));
	ubifs_assert(!(c->bi.data_growth & 7));
	ubifs_assert(!(c->bi.dd_growth & 7));
	spin_unlock(&c->space_lock);
}

/**
 * ubifs_convert_page_budget - convert budget of a new page.
 * @c: UBIFS file-system description object
 *
 * This function converts budget which was allocated for a new page of data to
 * the budget of changing an existing page of data. The latter is smaller than
 * the former, so this function only does simple re-calculation and does not
 * involve any write-back.
 */
void ubifs_convert_page_budget(struct ubifs_info *c)
{
	spin_lock(&c->space_lock);
	/* Release the index growth reservation */
	c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;
	/* Release the data growth reservation */
	c->bi.data_growth -= c->bi.page_budget;
	/* Increase the dirty data growth reservation instead */
	c->bi.dd_growth += c->bi.page_budget;
	/* And re-calculate the indexing space reservation */
	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
	spin_unlock(&c->space_lock);
}

/**
 * ubifs_release_dirty_inode_budget - release dirty inode budget.
 * @c: UBIFS file-system description object
 * @ui: UBIFS inode to release the budget for
 *
 * This function releases budget corresponding to a dirty inode. It is usually
 * called when after the inode has been written to the media and marked as
 * clean. It also causes the "no space" flags to be cleared.
 */
void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
				      struct ubifs_inode *ui)
{
	struct ubifs_budget_req req;

	memset(&req, 0, sizeof(struct ubifs_budget_req));
	/* The "no space" flags will be cleared because dd_growth is > 0 */
	req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);
	ubifs_release_budget(c, &req);
}

/**
 * ubifs_reported_space - calculate reported free space.
 * @c: the UBIFS file-system description object
 * @free: amount of free space
 *
 * This function calculates amount of free space which will be reported to
 * user-space. User-space application tend to expect that if the file-system
 * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
 * are able to write a file of size N. UBIFS attaches node headers to each data
 * node and it has to write indexing nodes as well. This introduces additional
 * overhead, and UBIFS has to report slightly less free space to meet the above
 * expectations.
 *
 * This function assumes free space is made up of uncompressed data nodes and
 * full index nodes (one per data node, tripled because we always allow enough
 * space to write the index thrice).
 *
 * Note, the calculation is pessimistic, which means that most of the time
 * UBIFS reports less space than it actually has.
 */
long long ubifs_reported_space(const struct ubifs_info *c, long long free)
{
	int divisor, factor, f;

	/*
	 * Reported space size is @free * X, where X is UBIFS block size
	 * divided by UBIFS block size + all overhead one data block
	 * introduces. The overhead is the node header + indexing overhead.
	 *
	 * Indexing overhead calculations are based on the following formula:
	 * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
	 * of data nodes, f - fanout. Because effective UBIFS fanout is twice
	 * as less than maximum fanout, we assume that each data node
	 * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
	 * Note, the multiplier 3 is because UBIFS reserves thrice as more space
	 * for the index.
	 */
	f = c->fanout > 3 ? c->fanout >> 1 : 2;
	factor = UBIFS_BLOCK_SIZE;
	divisor = UBIFS_MAX_DATA_NODE_SZ;
	divisor += (c->max_idx_node_sz * 3) / (f - 1);
	free *= factor;
	return div_u64(free, divisor);
}

/**
 * ubifs_get_free_space_nolock - return amount of free space.
 * @c: UBIFS file-system description object
 *
 * This function calculates amount of free space to report to user-space.
 *
 * Because UBIFS may introduce substantial overhead (the index, node headers,
 * alignment, wastage at the end of LEBs, etc), it cannot report real amount of
 * free flash space it has (well, because not all dirty space is reclaimable,
 * UBIFS does not actually know the real amount). If UBIFS did so, it would
 * bread user expectations about what free space is. Users seem to accustomed
 * to assume that if the file-system reports N bytes of free space, they would
 * be able to fit a file of N bytes to the FS. This almost works for
 * traditional file-systems, because they have way less overhead than UBIFS.
 * So, to keep users happy, UBIFS tries to take the overhead into account.
 */
long long ubifs_get_free_space_nolock(struct ubifs_info *c)
{
	int rsvd_idx_lebs, lebs;
	long long available, outstanding, free;

	ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
	outstanding = c->bi.data_growth + c->bi.dd_growth;
	available = ubifs_calc_available(c, c->bi.min_idx_lebs);

	/*
	 * When reporting free space to user-space, UBIFS guarantees that it is
	 * possible to write a file of free space size. This means that for
	 * empty LEBs we may use more precise calculations than
	 * 'ubifs_calc_available()' is using. Namely, we know that in empty
	 * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
	 * Thus, amend the available space.
	 *
	 * Note, the calculations below are similar to what we have in
	 * 'do_budget_space()', so refer there for comments.
	 */
	if (c->bi.min_idx_lebs > c->lst.idx_lebs)
		rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;
	else
		rsvd_idx_lebs = 0;
	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
	       c->lst.taken_empty_lebs;
	lebs -= rsvd_idx_lebs;
	available += lebs * (c->dark_wm - c->leb_overhead);

	if (available > outstanding)
		free = ubifs_reported_space(c, available - outstanding);
	else
		free = 0;
	return free;
}

/**
 * ubifs_get_free_space - return amount of free space.
 * @c: UBIFS file-system description object
 *
 * This function calculates and returns amount of free space to report to
 * user-space.
 */
long long ubifs_get_free_space(struct ubifs_info *c)
{
	long long free;

	spin_lock(&c->space_lock);
	free = ubifs_get_free_space_nolock(c);
	spin_unlock(&c->space_lock);

	return free;
}