1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * This file is part of UBIFS.
   4 *
   5 * Copyright (C) 2006-2008 Nokia Corporation.
   6 *
   7 * Authors: Adrian Hunter
   8 *          Artem Bityutskiy (Битюцкий Артём)
   9 */
  10
  11/*
  12 * This file implements garbage collection. The procedure for garbage collection
  13 * is different depending on whether a LEB as an index LEB (contains index
  14 * nodes) or not. For non-index LEBs, garbage collection finds a LEB which
  15 * contains a lot of dirty space (obsolete nodes), and copies the non-obsolete
  16 * nodes to the journal, at which point the garbage-collected LEB is free to be
  17 * reused. For index LEBs, garbage collection marks the non-obsolete index nodes
  18 * dirty in the TNC, and after the next commit, the garbage-collected LEB is
  19 * to be reused. Garbage collection will cause the number of dirty index nodes
  20 * to grow, however sufficient space is reserved for the index to ensure the
  21 * commit will never run out of space.
  22 *
  23 * Notes about dead watermark. At current UBIFS implementation we assume that
  24 * LEBs which have less than @c->dead_wm bytes of free + dirty space are full
  25 * and not worth garbage-collecting. The dead watermark is one min. I/O unit
  26 * size, or min. UBIFS node size, depending on what is greater. Indeed, UBIFS
  27 * Garbage Collector has to synchronize the GC head's write buffer before
  28 * returning, so this is about wasting one min. I/O unit. However, UBIFS GC can
  29 * actually reclaim even very small pieces of dirty space by garbage collecting
  30 * enough dirty LEBs, but we do not bother doing this at this implementation.
  31 *
  32 * Notes about dark watermark. The results of GC work depends on how big are
  33 * the UBIFS nodes GC deals with. Large nodes make GC waste more space. Indeed,
  34 * if GC move data from LEB A to LEB B and nodes in LEB A are large, GC would
  35 * have to waste large pieces of free space at the end of LEB B, because nodes
  36 * from LEB A would not fit. And the worst situation is when all nodes are of
  37 * maximum size. So dark watermark is the amount of free + dirty space in LEB
  38 * which are guaranteed to be reclaimable. If LEB has less space, the GC might
  39 * be unable to reclaim it. So, LEBs with free + dirty greater than dark
  40 * watermark are "good" LEBs from GC's point of view. The other LEBs are not so
  41 * good, and GC takes extra care when moving them.
  42 */
  43
  44#include <linux/slab.h>
  45#include <linux/pagemap.h>
  46#include <linux/list_sort.h>
  47#include "ubifs.h"
  48
  49/*
  50 * GC may need to move more than one LEB to make progress. The below constants
  51 * define "soft" and "hard" limits on the number of LEBs the garbage collector
  52 * may move.
  53 */
  54#define SOFT_LEBS_LIMIT 4
  55#define HARD_LEBS_LIMIT 32
  56
  57/**
  58 * switch_gc_head - switch the garbage collection journal head.
  59 * @c: UBIFS file-system description object
  60 * @buf: buffer to write
  61 * @len: length of the buffer to write
  62 * @lnum: LEB number written is returned here
  63 * @offs: offset written is returned here
  64 *
  65 * This function switch the GC head to the next LEB which is reserved in
  66 * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,
  67 * and other negative error code in case of failures.
  68 */
  69static int switch_gc_head(struct ubifs_info *c)
  70{
  71	int err, gc_lnum = c->gc_lnum;
  72	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
  73
  74	ubifs_assert(c, gc_lnum != -1);
  75	dbg_gc("switch GC head from LEB %d:%d to LEB %d (waste %d bytes)",
  76	       wbuf->lnum, wbuf->offs + wbuf->used, gc_lnum,
  77	       c->leb_size - wbuf->offs - wbuf->used);
  78
  79	err = ubifs_wbuf_sync_nolock(wbuf);
  80	if (err)
  81		return err;
  82
  83	/*
  84	 * The GC write-buffer was synchronized, we may safely unmap
  85	 * 'c->gc_lnum'.
  86	 */
  87	err = ubifs_leb_unmap(c, gc_lnum);
  88	if (err)
  89		return err;
  90
  91	err = ubifs_add_bud_to_log(c, GCHD, gc_lnum, 0);
  92	if (err)
  93		return err;
  94
  95	c->gc_lnum = -1;
  96	err = ubifs_wbuf_seek_nolock(wbuf, gc_lnum, 0);
  97	return err;
  98}
  99
 100/**
 101 * data_nodes_cmp - compare 2 data nodes.
 102 * @priv: UBIFS file-system description object
 103 * @a: first data node
 104 * @b: second data node
 105 *
 106 * This function compares data nodes @a and @b. Returns %1 if @a has greater
 107 * inode or block number, and %-1 otherwise.
 108 */
 109static int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
 110{
 111	ino_t inuma, inumb;
 112	struct ubifs_info *c = priv;
 113	struct ubifs_scan_node *sa, *sb;
 114
 115	cond_resched();
 116	if (a == b)
 117		return 0;
 118
 119	sa = list_entry(a, struct ubifs_scan_node, list);
 120	sb = list_entry(b, struct ubifs_scan_node, list);
 121
 122	ubifs_assert(c, key_type(c, &sa->key) == UBIFS_DATA_KEY);
 123	ubifs_assert(c, key_type(c, &sb->key) == UBIFS_DATA_KEY);
 124	ubifs_assert(c, sa->type == UBIFS_DATA_NODE);
 125	ubifs_assert(c, sb->type == UBIFS_DATA_NODE);
 126
 127	inuma = key_inum(c, &sa->key);
 128	inumb = key_inum(c, &sb->key);
 129
 130	if (inuma == inumb) {
 131		unsigned int blka = key_block(c, &sa->key);
 132		unsigned int blkb = key_block(c, &sb->key);
 133
 134		if (blka <= blkb)
 135			return -1;
 136	} else if (inuma <= inumb)
 137		return -1;
 138
 139	return 1;
 140}
 141
 142/*
 143 * nondata_nodes_cmp - compare 2 non-data nodes.
 144 * @priv: UBIFS file-system description object
 145 * @a: first node
 146 * @a: second node
 147 *
 148 * This function compares nodes @a and @b. It makes sure that inode nodes go
 149 * first and sorted by length in descending order. Directory entry nodes go
 150 * after inode nodes and are sorted in ascending hash valuer order.
 151 */
 152static int nondata_nodes_cmp(void *priv, struct list_head *a,
 153			     struct list_head *b)
 154{
 155	ino_t inuma, inumb;
 156	struct ubifs_info *c = priv;
 157	struct ubifs_scan_node *sa, *sb;
 158
 159	cond_resched();
 160	if (a == b)
 161		return 0;
 162
 163	sa = list_entry(a, struct ubifs_scan_node, list);
 164	sb = list_entry(b, struct ubifs_scan_node, list);
 165
 166	ubifs_assert(c, key_type(c, &sa->key) != UBIFS_DATA_KEY &&
 167		     key_type(c, &sb->key) != UBIFS_DATA_KEY);
 168	ubifs_assert(c, sa->type != UBIFS_DATA_NODE &&
 169		     sb->type != UBIFS_DATA_NODE);
 170
 171	/* Inodes go before directory entries */
 172	if (sa->type == UBIFS_INO_NODE) {
 173		if (sb->type == UBIFS_INO_NODE)
 174			return sb->len - sa->len;
 175		return -1;
 176	}
 177	if (sb->type == UBIFS_INO_NODE)
 178		return 1;
 179
 180	ubifs_assert(c, key_type(c, &sa->key) == UBIFS_DENT_KEY ||
 181		     key_type(c, &sa->key) == UBIFS_XENT_KEY);
 182	ubifs_assert(c, key_type(c, &sb->key) == UBIFS_DENT_KEY ||
 183		     key_type(c, &sb->key) == UBIFS_XENT_KEY);
 184	ubifs_assert(c, sa->type == UBIFS_DENT_NODE ||
 185		     sa->type == UBIFS_XENT_NODE);
 186	ubifs_assert(c, sb->type == UBIFS_DENT_NODE ||
 187		     sb->type == UBIFS_XENT_NODE);
 188
 189	inuma = key_inum(c, &sa->key);
 190	inumb = key_inum(c, &sb->key);
 191
 192	if (inuma == inumb) {
 193		uint32_t hasha = key_hash(c, &sa->key);
 194		uint32_t hashb = key_hash(c, &sb->key);
 195
 196		if (hasha <= hashb)
 197			return -1;
 198	} else if (inuma <= inumb)
 199		return -1;
 200
 201	return 1;
 202}
 203
 204/**
 205 * sort_nodes - sort nodes for GC.
 206 * @c: UBIFS file-system description object
 207 * @sleb: describes nodes to sort and contains the result on exit
 208 * @nondata: contains non-data nodes on exit
 209 * @min: minimum node size is returned here
 210 *
 211 * This function sorts the list of inodes to garbage collect. First of all, it
 212 * kills obsolete nodes and separates data and non-data nodes to the
 213 * @sleb->nodes and @nondata lists correspondingly.
 214 *
 215 * Data nodes are then sorted in block number order - this is important for
 216 * bulk-read; data nodes with lower inode number go before data nodes with
 217 * higher inode number, and data nodes with lower block number go before data
 218 * nodes with higher block number;
 219 *
 220 * Non-data nodes are sorted as follows.
 221 *   o First go inode nodes - they are sorted in descending length order.
 222 *   o Then go directory entry nodes - they are sorted in hash order, which
 223 *     should supposedly optimize 'readdir()'. Direntry nodes with lower parent
 224 *     inode number go before direntry nodes with higher parent inode number,
 225 *     and direntry nodes with lower name hash values go before direntry nodes
 226 *     with higher name hash values.
 227 *
 228 * This function returns zero in case of success and a negative error code in
 229 * case of failure.
 230 */
 231static int sort_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 232		      struct list_head *nondata, int *min)
 233{
 234	int err;
 235	struct ubifs_scan_node *snod, *tmp;
 236
 237	*min = INT_MAX;
 238
 239	/* Separate data nodes and non-data nodes */
 240	list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
 241		ubifs_assert(c, snod->type == UBIFS_INO_NODE  ||
 242			     snod->type == UBIFS_DATA_NODE ||
 243			     snod->type == UBIFS_DENT_NODE ||
 244			     snod->type == UBIFS_XENT_NODE ||
 245			     snod->type == UBIFS_TRUN_NODE ||
 246			     snod->type == UBIFS_AUTH_NODE);
 247
 248		if (snod->type != UBIFS_INO_NODE  &&
 249		    snod->type != UBIFS_DATA_NODE &&
 250		    snod->type != UBIFS_DENT_NODE &&
 251		    snod->type != UBIFS_XENT_NODE) {
 252			/* Probably truncation node, zap it */
 253			list_del(&snod->list);
 254			kfree(snod);
 255			continue;
 256		}
 257
 258		ubifs_assert(c, key_type(c, &snod->key) == UBIFS_DATA_KEY ||
 259			     key_type(c, &snod->key) == UBIFS_INO_KEY  ||
 260			     key_type(c, &snod->key) == UBIFS_DENT_KEY ||
 261			     key_type(c, &snod->key) == UBIFS_XENT_KEY);
 262
 263		err = ubifs_tnc_has_node(c, &snod->key, 0, sleb->lnum,
 264					 snod->offs, 0);
 265		if (err < 0)
 266			return err;
 267
 268		if (!err) {
 269			/* The node is obsolete, remove it from the list */
 270			list_del(&snod->list);
 271			kfree(snod);
 272			continue;
 273		}
 274
 275		if (snod->len < *min)
 276			*min = snod->len;
 277
 278		if (key_type(c, &snod->key) != UBIFS_DATA_KEY)
 279			list_move_tail(&snod->list, nondata);
 280	}
 281
 282	/* Sort data and non-data nodes */
 283	list_sort(c, &sleb->nodes, &data_nodes_cmp);
 284	list_sort(c, nondata, &nondata_nodes_cmp);
 285
 286	err = dbg_check_data_nodes_order(c, &sleb->nodes);
 287	if (err)
 288		return err;
 289	err = dbg_check_nondata_nodes_order(c, nondata);
 290	if (err)
 291		return err;
 292	return 0;
 293}
 294
 295/**
 296 * move_node - move a node.
 297 * @c: UBIFS file-system description object
 298 * @sleb: describes the LEB to move nodes from
 299 * @snod: the mode to move
 300 * @wbuf: write-buffer to move node to
 301 *
 302 * This function moves node @snod to @wbuf, changes TNC correspondingly, and
 303 * destroys @snod. Returns zero in case of success and a negative error code in
 304 * case of failure.
 305 */
 306static int move_node(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 307		     struct ubifs_scan_node *snod, struct ubifs_wbuf *wbuf)
 308{
 309	int err, new_lnum = wbuf->lnum, new_offs = wbuf->offs + wbuf->used;
 310
 311	cond_resched();
 312	err = ubifs_wbuf_write_nolock(wbuf, snod->node, snod->len);
 313	if (err)
 314		return err;
 315
 316	err = ubifs_tnc_replace(c, &snod->key, sleb->lnum,
 317				snod->offs, new_lnum, new_offs,
 318				snod->len);
 319	list_del(&snod->list);
 320	kfree(snod);
 321	return err;
 322}
 323
 324/**
 325 * move_nodes - move nodes.
 326 * @c: UBIFS file-system description object
 327 * @sleb: describes the LEB to move nodes from
 328 *
 329 * This function moves valid nodes from data LEB described by @sleb to the GC
 330 * journal head. This function returns zero in case of success, %-EAGAIN if
 331 * commit is required, and other negative error codes in case of other
 332 * failures.
 333 */
 334static int move_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb)
 335{
 336	int err, min;
 337	LIST_HEAD(nondata);
 338	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 339
 340	if (wbuf->lnum == -1) {
 341		/*
 342		 * The GC journal head is not set, because it is the first GC
 343		 * invocation since mount.
 344		 */
 345		err = switch_gc_head(c);
 346		if (err)
 347			return err;
 348	}
 349
 350	err = sort_nodes(c, sleb, &nondata, &min);
 351	if (err)
 352		goto out;
 353
 354	/* Write nodes to their new location. Use the first-fit strategy */
 355	while (1) {
 356		int avail, moved = 0;
 357		struct ubifs_scan_node *snod, *tmp;
 358
 359		/* Move data nodes */
 360		list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
 361			avail = c->leb_size - wbuf->offs - wbuf->used -
 362					ubifs_auth_node_sz(c);
 363			if  (snod->len > avail)
 364				/*
 365				 * Do not skip data nodes in order to optimize
 366				 * bulk-read.
 367				 */
 368				break;
 369
 370			err = ubifs_shash_update(c, c->jheads[GCHD].log_hash,
 371						 snod->node, snod->len);
 372			if (err)
 373				goto out;
 374
 375			err = move_node(c, sleb, snod, wbuf);
 376			if (err)
 377				goto out;
 378			moved = 1;
 379		}
 380
 381		/* Move non-data nodes */
 382		list_for_each_entry_safe(snod, tmp, &nondata, list) {
 383			avail = c->leb_size - wbuf->offs - wbuf->used -
 384					ubifs_auth_node_sz(c);
 385			if (avail < min)
 386				break;
 387
 388			if  (snod->len > avail) {
 389				/*
 390				 * Keep going only if this is an inode with
 391				 * some data. Otherwise stop and switch the GC
 392				 * head. IOW, we assume that data-less inode
 393				 * nodes and direntry nodes are roughly of the
 394				 * same size.
 395				 */
 396				if (key_type(c, &snod->key) == UBIFS_DENT_KEY ||
 397				    snod->len == UBIFS_INO_NODE_SZ)
 398					break;
 399				continue;
 400			}
 401
 402			err = ubifs_shash_update(c, c->jheads[GCHD].log_hash,
 403						 snod->node, snod->len);
 404			if (err)
 405				goto out;
 406
 407			err = move_node(c, sleb, snod, wbuf);
 408			if (err)
 409				goto out;
 410			moved = 1;
 411		}
 412
 413		if (ubifs_authenticated(c) && moved) {
 414			struct ubifs_auth_node *auth;
 415
 416			auth = kmalloc(ubifs_auth_node_sz(c), GFP_NOFS);
 417			if (!auth) {
 418				err = -ENOMEM;
 419				goto out;
 420			}
 421
 422			err = ubifs_prepare_auth_node(c, auth,
 423						c->jheads[GCHD].log_hash);
 424			if (err) {
 425				kfree(auth);
 426				goto out;
 427			}
 428
 429			err = ubifs_wbuf_write_nolock(wbuf, auth,
 430						      ubifs_auth_node_sz(c));
 431			if (err) {
 432				kfree(auth);
 433				goto out;
 434			}
 435
 436			ubifs_add_dirt(c, wbuf->lnum, ubifs_auth_node_sz(c));
 437		}
 438
 439		if (list_empty(&sleb->nodes) && list_empty(&nondata))
 440			break;
 441
 442		/*
 443		 * Waste the rest of the space in the LEB and switch to the
 444		 * next LEB.
 445		 */
 446		err = switch_gc_head(c);
 447		if (err)
 448			goto out;
 449	}
 450
 451	return 0;
 452
 453out:
 454	list_splice_tail(&nondata, &sleb->nodes);
 455	return err;
 456}
 457
 458/**
 459 * gc_sync_wbufs - sync write-buffers for GC.
 460 * @c: UBIFS file-system description object
 461 *
 462 * We must guarantee that obsoleting nodes are on flash. Unfortunately they may
 463 * be in a write-buffer instead. That is, a node could be written to a
 464 * write-buffer, obsoleting another node in a LEB that is GC'd. If that LEB is
 465 * erased before the write-buffer is sync'd and then there is an unclean
 466 * unmount, then an existing node is lost. To avoid this, we sync all
 467 * write-buffers.
 468 *
 469 * This function returns %0 on success or a negative error code on failure.
 470 */
 471static int gc_sync_wbufs(struct ubifs_info *c)
 472{
 473	int err, i;
 474
 475	for (i = 0; i < c->jhead_cnt; i++) {
 476		if (i == GCHD)
 477			continue;
 478		err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
 479		if (err)
 480			return err;
 481	}
 482	return 0;
 483}
 484
 485/**
 486 * ubifs_garbage_collect_leb - garbage-collect a logical eraseblock.
 487 * @c: UBIFS file-system description object
 488 * @lp: describes the LEB to garbage collect
 489 *
 490 * This function garbage-collects an LEB and returns one of the @LEB_FREED,
 491 * @LEB_RETAINED, etc positive codes in case of success, %-EAGAIN if commit is
 492 * required, and other negative error codes in case of failures.
 493 */
 494int ubifs_garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp)
 495{
 496	struct ubifs_scan_leb *sleb;
 497	struct ubifs_scan_node *snod;
 498	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 499	int err = 0, lnum = lp->lnum;
 500
 501	ubifs_assert(c, c->gc_lnum != -1 || wbuf->offs + wbuf->used == 0 ||
 502		     c->need_recovery);
 503	ubifs_assert(c, c->gc_lnum != lnum);
 504	ubifs_assert(c, wbuf->lnum != lnum);
 505
 506	if (lp->free + lp->dirty == c->leb_size) {
 507		/* Special case - a free LEB  */
 508		dbg_gc("LEB %d is free, return it", lp->lnum);
 509		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
 510
 511		if (lp->free != c->leb_size) {
 512			/*
 513			 * Write buffers must be sync'd before unmapping
 514			 * freeable LEBs, because one of them may contain data
 515			 * which obsoletes something in 'lp->lnum'.
 516			 */
 517			err = gc_sync_wbufs(c);
 518			if (err)
 519				return err;
 520			err = ubifs_change_one_lp(c, lp->lnum, c->leb_size,
 521						  0, 0, 0, 0);
 522			if (err)
 523				return err;
 524		}
 525		err = ubifs_leb_unmap(c, lp->lnum);
 526		if (err)
 527			return err;
 528
 529		if (c->gc_lnum == -1) {
 530			c->gc_lnum = lnum;
 531			return LEB_RETAINED;
 532		}
 533
 534		return LEB_FREED;
 535	}
 536
 537	/*
 538	 * We scan the entire LEB even though we only really need to scan up to
 539	 * (c->leb_size - lp->free).
 540	 */
 541	sleb = ubifs_scan(c, lnum, 0, c->sbuf, 0);
 542	if (IS_ERR(sleb))
 543		return PTR_ERR(sleb);
 544
 545	ubifs_assert(c, !list_empty(&sleb->nodes));
 546	snod = list_entry(sleb->nodes.next, struct ubifs_scan_node, list);
 547
 548	if (snod->type == UBIFS_IDX_NODE) {
 549		struct ubifs_gced_idx_leb *idx_gc;
 550
 551		dbg_gc("indexing LEB %d (free %d, dirty %d)",
 552		       lnum, lp->free, lp->dirty);
 553		list_for_each_entry(snod, &sleb->nodes, list) {
 554			struct ubifs_idx_node *idx = snod->node;
 555			int level = le16_to_cpu(idx->level);
 556
 557			ubifs_assert(c, snod->type == UBIFS_IDX_NODE);
 558			key_read(c, ubifs_idx_key(c, idx), &snod->key);
 559			err = ubifs_dirty_idx_node(c, &snod->key, level, lnum,
 560						   snod->offs);
 561			if (err)
 562				goto out;
 563		}
 564
 565		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
 566		if (!idx_gc) {
 567			err = -ENOMEM;
 568			goto out;
 569		}
 570
 571		idx_gc->lnum = lnum;
 572		idx_gc->unmap = 0;
 573		list_add(&idx_gc->list, &c->idx_gc);
 574
 575		/*
 576		 * Don't release the LEB until after the next commit, because
 577		 * it may contain data which is needed for recovery. So
 578		 * although we freed this LEB, it will become usable only after
 579		 * the commit.
 580		 */
 581		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0,
 582					  LPROPS_INDEX, 1);
 583		if (err)
 584			goto out;
 585		err = LEB_FREED_IDX;
 586	} else {
 587		dbg_gc("data LEB %d (free %d, dirty %d)",
 588		       lnum, lp->free, lp->dirty);
 589
 590		err = move_nodes(c, sleb);
 591		if (err)
 592			goto out_inc_seq;
 593
 594		err = gc_sync_wbufs(c);
 595		if (err)
 596			goto out_inc_seq;
 597
 598		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0, 0, 0);
 599		if (err)
 600			goto out_inc_seq;
 601
 602		/* Allow for races with TNC */
 603		c->gced_lnum = lnum;
 604		smp_wmb();
 605		c->gc_seq += 1;
 606		smp_wmb();
 607
 608		if (c->gc_lnum == -1) {
 609			c->gc_lnum = lnum;
 610			err = LEB_RETAINED;
 611		} else {
 612			err = ubifs_wbuf_sync_nolock(wbuf);
 613			if (err)
 614				goto out;
 615
 616			err = ubifs_leb_unmap(c, lnum);
 617			if (err)
 618				goto out;
 619
 620			err = LEB_FREED;
 621		}
 622	}
 623
 624out:
 625	ubifs_scan_destroy(sleb);
 626	return err;
 627
 628out_inc_seq:
 629	/* We may have moved at least some nodes so allow for races with TNC */
 630	c->gced_lnum = lnum;
 631	smp_wmb();
 632	c->gc_seq += 1;
 633	smp_wmb();
 634	goto out;
 635}
 636
 637/**
 638 * ubifs_garbage_collect - UBIFS garbage collector.
 639 * @c: UBIFS file-system description object
 640 * @anyway: do GC even if there are free LEBs
 641 *
 642 * This function does out-of-place garbage collection. The return codes are:
 643 *   o positive LEB number if the LEB has been freed and may be used;
 644 *   o %-EAGAIN if the caller has to run commit;
 645 *   o %-ENOSPC if GC failed to make any progress;
 646 *   o other negative error codes in case of other errors.
 647 *
 648 * Garbage collector writes data to the journal when GC'ing data LEBs, and just
 649 * marking indexing nodes dirty when GC'ing indexing LEBs. Thus, at some point
 650 * commit may be required. But commit cannot be run from inside GC, because the
 651 * caller might be holding the commit lock, so %-EAGAIN is returned instead;
 652 * And this error code means that the caller has to run commit, and re-run GC
 653 * if there is still no free space.
 654 *
 655 * There are many reasons why this function may return %-EAGAIN:
 656 * o the log is full and there is no space to write an LEB reference for
 657 *   @c->gc_lnum;
 658 * o the journal is too large and exceeds size limitations;
 659 * o GC moved indexing LEBs, but they can be used only after the commit;
 660 * o the shrinker fails to find clean znodes to free and requests the commit;
 661 * o etc.
 662 *
 663 * Note, if the file-system is close to be full, this function may return
 664 * %-EAGAIN infinitely, so the caller has to limit amount of re-invocations of
 665 * the function. E.g., this happens if the limits on the journal size are too
 666 * tough and GC writes too much to the journal before an LEB is freed. This
 667 * might also mean that the journal is too large, and the TNC becomes to big,
 668 * so that the shrinker is constantly called, finds not clean znodes to free,
 669 * and requests commit. Well, this may also happen if the journal is all right,
 670 * but another kernel process consumes too much memory. Anyway, infinite
 671 * %-EAGAIN may happen, but in some extreme/misconfiguration cases.
 672 */
 673int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
 674{
 675	int i, err, ret, min_space = c->dead_wm;
 676	struct ubifs_lprops lp;
 677	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 678
 679	ubifs_assert_cmt_locked(c);
 680	ubifs_assert(c, !c->ro_media && !c->ro_mount);
 681
 682	if (ubifs_gc_should_commit(c))
 683		return -EAGAIN;
 684
 685	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
 686
 687	if (c->ro_error) {
 688		ret = -EROFS;
 689		goto out_unlock;
 690	}
 691
 692	/* We expect the write-buffer to be empty on entry */
 693	ubifs_assert(c, !wbuf->used);
 694
 695	for (i = 0; ; i++) {
 696		int space_before, space_after;
 697
 698		cond_resched();
 699
 700		/* Give the commit an opportunity to run */
 701		if (ubifs_gc_should_commit(c)) {
 702			ret = -EAGAIN;
 703			break;
 704		}
 705
 706		if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
 707			/*
 708			 * We've done enough iterations. Indexing LEBs were
 709			 * moved and will be available after the commit.
 710			 */
 711			dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
 712			ubifs_commit_required(c);
 713			ret = -EAGAIN;
 714			break;
 715		}
 716
 717		if (i > HARD_LEBS_LIMIT) {
 718			/*
 719			 * We've moved too many LEBs and have not made
 720			 * progress, give up.
 721			 */
 722			dbg_gc("hard limit, -ENOSPC");
 723			ret = -ENOSPC;
 724			break;
 725		}
 726
 727		/*
 728		 * Empty and freeable LEBs can turn up while we waited for
 729		 * the wbuf lock, or while we have been running GC. In that
 730		 * case, we should just return one of those instead of
 731		 * continuing to GC dirty LEBs. Hence we request
 732		 * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
 733		 */
 734		ret = ubifs_find_dirty_leb(c, &lp, min_space, anyway ? 0 : 1);
 735		if (ret) {
 736			if (ret == -ENOSPC)
 737				dbg_gc("no more dirty LEBs");
 738			break;
 739		}
 740
 741		dbg_gc("found LEB %d: free %d, dirty %d, sum %d (min. space %d)",
 742		       lp.lnum, lp.free, lp.dirty, lp.free + lp.dirty,
 743		       min_space);
 744
 745		space_before = c->leb_size - wbuf->offs - wbuf->used;
 746		if (wbuf->lnum == -1)
 747			space_before = 0;
 748
 749		ret = ubifs_garbage_collect_leb(c, &lp);
 750		if (ret < 0) {
 751			if (ret == -EAGAIN) {
 752				/*
 753				 * This is not error, so we have to return the
 754				 * LEB to lprops. But if 'ubifs_return_leb()'
 755				 * fails, its failure code is propagated to the
 756				 * caller instead of the original '-EAGAIN'.
 757				 */
 758				err = ubifs_return_leb(c, lp.lnum);
 759				if (err)
 760					ret = err;
 761				break;
 762			}
 763			goto out;
 764		}
 765
 766		if (ret == LEB_FREED) {
 767			/* An LEB has been freed and is ready for use */
 768			dbg_gc("LEB %d freed, return", lp.lnum);
 769			ret = lp.lnum;
 770			break;
 771		}
 772
 773		if (ret == LEB_FREED_IDX) {
 774			/*
 775			 * This was an indexing LEB and it cannot be
 776			 * immediately used. And instead of requesting the
 777			 * commit straight away, we try to garbage collect some
 778			 * more.
 779			 */
 780			dbg_gc("indexing LEB %d freed, continue", lp.lnum);
 781			continue;
 782		}
 783
 784		ubifs_assert(c, ret == LEB_RETAINED);
 785		space_after = c->leb_size - wbuf->offs - wbuf->used;
 786		dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
 787		       space_after - space_before);
 788
 789		if (space_after > space_before) {
 790			/* GC makes progress, keep working */
 791			min_space >>= 1;
 792			if (min_space < c->dead_wm)
 793				min_space = c->dead_wm;
 794			continue;
 795		}
 796
 797		dbg_gc("did not make progress");
 798
 799		/*
 800		 * GC moved an LEB bud have not done any progress. This means
 801		 * that the previous GC head LEB contained too few free space
 802		 * and the LEB which was GC'ed contained only large nodes which
 803		 * did not fit that space.
 804		 *
 805		 * We can do 2 things:
 806		 * 1. pick another LEB in a hope it'll contain a small node
 807		 *    which will fit the space we have at the end of current GC
 808		 *    head LEB, but there is no guarantee, so we try this out
 809		 *    unless we have already been working for too long;
 810		 * 2. request an LEB with more dirty space, which will force
 811		 *    'ubifs_find_dirty_leb()' to start scanning the lprops
 812		 *    table, instead of just picking one from the heap
 813		 *    (previously it already picked the dirtiest LEB).
 814		 */
 815		if (i < SOFT_LEBS_LIMIT) {
 816			dbg_gc("try again");
 817			continue;
 818		}
 819
 820		min_space <<= 1;
 821		if (min_space > c->dark_wm)
 822			min_space = c->dark_wm;
 823		dbg_gc("set min. space to %d", min_space);
 824	}
 825
 826	if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
 827		dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
 828		ubifs_commit_required(c);
 829		ret = -EAGAIN;
 830	}
 831
 832	err = ubifs_wbuf_sync_nolock(wbuf);
 833	if (!err)
 834		err = ubifs_leb_unmap(c, c->gc_lnum);
 835	if (err) {
 836		ret = err;
 837		goto out;
 838	}
 839out_unlock:
 840	mutex_unlock(&wbuf->io_mutex);
 841	return ret;
 842
 843out:
 844	ubifs_assert(c, ret < 0);
 845	ubifs_assert(c, ret != -ENOSPC && ret != -EAGAIN);
 846	ubifs_wbuf_sync_nolock(wbuf);
 847	ubifs_ro_mode(c, ret);
 848	mutex_unlock(&wbuf->io_mutex);
 849	ubifs_return_leb(c, lp.lnum);
 850	return ret;
 851}
 852
 853/**
 854 * ubifs_gc_start_commit - garbage collection at start of commit.
 855 * @c: UBIFS file-system description object
 856 *
 857 * If a LEB has only dirty and free space, then we may safely unmap it and make
 858 * it free.  Note, we cannot do this with indexing LEBs because dirty space may
 859 * correspond index nodes that are required for recovery.  In that case, the
 860 * LEB cannot be unmapped until after the next commit.
 861 *
 862 * This function returns %0 upon success and a negative error code upon failure.
 863 */
 864int ubifs_gc_start_commit(struct ubifs_info *c)
 865{
 866	struct ubifs_gced_idx_leb *idx_gc;
 867	const struct ubifs_lprops *lp;
 868	int err = 0, flags;
 869
 870	ubifs_get_lprops(c);
 871
 872	/*
 873	 * Unmap (non-index) freeable LEBs. Note that recovery requires that all
 874	 * wbufs are sync'd before this, which is done in 'do_commit()'.
 875	 */
 876	while (1) {
 877		lp = ubifs_fast_find_freeable(c);
 878		if (!lp)
 879			break;
 880		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
 881		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
 882		err = ubifs_leb_unmap(c, lp->lnum);
 883		if (err)
 884			goto out;
 885		lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
 886		if (IS_ERR(lp)) {
 887			err = PTR_ERR(lp);
 888			goto out;
 889		}
 890		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
 891		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
 892	}
 893
 894	/* Mark GC'd index LEBs OK to unmap after this commit finishes */
 895	list_for_each_entry(idx_gc, &c->idx_gc, list)
 896		idx_gc->unmap = 1;
 897
 898	/* Record index freeable LEBs for unmapping after commit */
 899	while (1) {
 900		lp = ubifs_fast_find_frdi_idx(c);
 901		if (IS_ERR(lp)) {
 902			err = PTR_ERR(lp);
 903			goto out;
 904		}
 905		if (!lp)
 906			break;
 907		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
 908		if (!idx_gc) {
 909			err = -ENOMEM;
 910			goto out;
 911		}
 912		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
 913		ubifs_assert(c, lp->flags & LPROPS_INDEX);
 914		/* Don't release the LEB until after the next commit */
 915		flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
 916		lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
 917		if (IS_ERR(lp)) {
 918			err = PTR_ERR(lp);
 919			kfree(idx_gc);
 920			goto out;
 921		}
 922		ubifs_assert(c, lp->flags & LPROPS_TAKEN);
 923		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
 924		idx_gc->lnum = lp->lnum;
 925		idx_gc->unmap = 1;
 926		list_add(&idx_gc->list, &c->idx_gc);
 927	}
 928out:
 929	ubifs_release_lprops(c);
 930	return err;
 931}
 932
 933/**
 934 * ubifs_gc_end_commit - garbage collection at end of commit.
 935 * @c: UBIFS file-system description object
 936 *
 937 * This function completes out-of-place garbage collection of index LEBs.
 938 */
 939int ubifs_gc_end_commit(struct ubifs_info *c)
 940{
 941	struct ubifs_gced_idx_leb *idx_gc, *tmp;
 942	struct ubifs_wbuf *wbuf;
 943	int err = 0;
 944
 945	wbuf = &c->jheads[GCHD].wbuf;
 946	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
 947	list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
 948		if (idx_gc->unmap) {
 949			dbg_gc("LEB %d", idx_gc->lnum);
 950			err = ubifs_leb_unmap(c, idx_gc->lnum);
 951			if (err)
 952				goto out;
 953			err = ubifs_change_one_lp(c, idx_gc->lnum, LPROPS_NC,
 954					  LPROPS_NC, 0, LPROPS_TAKEN, -1);
 955			if (err)
 956				goto out;
 957			list_del(&idx_gc->list);
 958			kfree(idx_gc);
 959		}
 960out:
 961	mutex_unlock(&wbuf->io_mutex);
 962	return err;
 963}
 964
 965/**
 966 * ubifs_destroy_idx_gc - destroy idx_gc list.
 967 * @c: UBIFS file-system description object
 968 *
 969 * This function destroys the @c->idx_gc list. It is called when unmounting
 970 * so locks are not needed. Returns zero in case of success and a negative
 971 * error code in case of failure.
 972 */
 973void ubifs_destroy_idx_gc(struct ubifs_info *c)
 974{
 975	while (!list_empty(&c->idx_gc)) {
 976		struct ubifs_gced_idx_leb *idx_gc;
 977
 978		idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
 979				    list);
 980		c->idx_gc_cnt -= 1;
 981		list_del(&idx_gc->list);
 982		kfree(idx_gc);
 983	}
 984}
 985
 986/**
 987 * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
 988 * @c: UBIFS file-system description object
 989 *
 990 * Called during start commit so locks are not needed.
 991 */
 992int ubifs_get_idx_gc_leb(struct ubifs_info *c)
 993{
 994	struct ubifs_gced_idx_leb *idx_gc;
 995	int lnum;
 996
 997	if (list_empty(&c->idx_gc))
 998		return -ENOSPC;
 999	idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
1000	lnum = idx_gc->lnum;
1001	/* c->idx_gc_cnt is updated by the caller when lprops are updated */
1002	list_del(&idx_gc->list);
1003	kfree(idx_gc);
1004	return lnum;
1005}