ubifs-utils: Import UBIFS libs from linux kernel

Import UBIFS libs from linux kernel. Next patches will replace ubifs
related source code with implementation of linux kernel, which makes
userspace implementation be same with linux kernel, then fsck.ubifs
can resuse the code.

Notice: lpt.c is modified with [1] applied. ubifs.h and orphan.c are
modified with [2] applied, journal.c is modified with [3] reverted(
because fsck runs in a single thread, so waitqueue is not needed to
be implemented in userspace.).
[1] https://lore.kernel.org/linux-mtd/20231228014112.2836317-13-chengzhihao1@huawei.com/
[2] https://lore.kernel.org/linux-mtd/20240410073751.2522830-1-chengzhihao1@huawei.com/
[3] https://lore.kernel.org/linux-mtd/20240122063103.359501-1-chengzhihao1@huawei.com/

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 1017 insertions, 0 deletions

diff --git a/ubifs-utils/libubifs/gc.c b/ubifs-utils/libubifs/gc.c
new file mode 100644
index 0000000..3134d07
--- /dev/null
+++ b/ubifs-utils/libubifs/gc.c
@@ -0,0 +1,1017 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This file is part of UBIFS.
+ *
+ * Copyright (C) 2006-2008 Nokia Corporation.
+ *
+ * Authors: Adrian Hunter
+ *          Artem Bityutskiy (Битюцкий Артём)
+ */
+
+/*
+ * This file implements garbage collection. The procedure for garbage collection
+ * is different depending on whether a LEB as an index LEB (contains index
+ * nodes) or not. For non-index LEBs, garbage collection finds a LEB which
+ * contains a lot of dirty space (obsolete nodes), and copies the non-obsolete
+ * nodes to the journal, at which point the garbage-collected LEB is free to be
+ * reused. For index LEBs, garbage collection marks the non-obsolete index nodes
+ * dirty in the TNC, and after the next commit, the garbage-collected LEB is
+ * to be reused. Garbage collection will cause the number of dirty index nodes
+ * to grow, however sufficient space is reserved for the index to ensure the
+ * commit will never run out of space.
+ *
+ * Notes about dead watermark. At current UBIFS implementation we assume that
+ * LEBs which have less than @c->dead_wm bytes of free + dirty space are full
+ * and not worth garbage-collecting. The dead watermark is one min. I/O unit
+ * size, or min. UBIFS node size, depending on what is greater. Indeed, UBIFS
+ * Garbage Collector has to synchronize the GC head's write buffer before
+ * returning, so this is about wasting one min. I/O unit. However, UBIFS GC can
+ * actually reclaim even very small pieces of dirty space by garbage collecting
+ * enough dirty LEBs, but we do not bother doing this at this implementation.
+ *
+ * Notes about dark watermark. The results of GC work depends on how big are
+ * the UBIFS nodes GC deals with. Large nodes make GC waste more space. Indeed,
+ * if GC move data from LEB A to LEB B and nodes in LEB A are large, GC would
+ * have to waste large pieces of free space at the end of LEB B, because nodes
+ * from LEB A would not fit. And the worst situation is when all nodes are of
+ * maximum size. So dark watermark is the amount of free + dirty space in LEB
+ * which are guaranteed to be reclaimable. If LEB has less space, the GC might
+ * be unable to reclaim it. So, LEBs with free + dirty greater than dark
+ * watermark are "good" LEBs from GC's point of view. The other LEBs are not so
+ * good, and GC takes extra care when moving them.
+ */
+
+#include <linux/slab.h>
+#include <linux/pagemap.h>
+#include <linux/list_sort.h>
+#include "ubifs.h"
+
+/*
+ * GC may need to move more than one LEB to make progress. The below constants
+ * define "soft" and "hard" limits on the number of LEBs the garbage collector
+ * may move.
+ */
+#define SOFT_LEBS_LIMIT 4
+#define HARD_LEBS_LIMIT 32
+
+/**
+ * switch_gc_head - switch the garbage collection journal head.
+ * @c: UBIFS file-system description object
+ *
+ * This function switch the GC head to the next LEB which is reserved in
+ * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,
+ * and other negative error code in case of failures.
+ */
+static int switch_gc_head(struct ubifs_info *c)
+{
+	int err, gc_lnum = c->gc_lnum;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+
+	ubifs_assert(c, gc_lnum != -1);
+	dbg_gc("switch GC head from LEB %d:%d to LEB %d (waste %d bytes)",
+	       wbuf->lnum, wbuf->offs + wbuf->used, gc_lnum,
+	       c->leb_size - wbuf->offs - wbuf->used);
+
+	err = ubifs_wbuf_sync_nolock(wbuf);
+	if (err)
+		return err;
+
+	/*
+	 * The GC write-buffer was synchronized, we may safely unmap
+	 * 'c->gc_lnum'.
+	 */
+	err = ubifs_leb_unmap(c, gc_lnum);
+	if (err)
+		return err;
+
+	err = ubifs_add_bud_to_log(c, GCHD, gc_lnum, 0);
+	if (err)
+		return err;
+
+	c->gc_lnum = -1;
+	err = ubifs_wbuf_seek_nolock(wbuf, gc_lnum, 0);
+	return err;
+}
+
+/**
+ * data_nodes_cmp - compare 2 data nodes.
+ * @priv: UBIFS file-system description object
+ * @a: first data node
+ * @b: second data node
+ *
+ * This function compares data nodes @a and @b. Returns %1 if @a has greater
+ * inode or block number, and %-1 otherwise.
+ */
+static int data_nodes_cmp(void *priv, const struct list_head *a,
+			  const struct list_head *b)
+{
+	ino_t inuma, inumb;
+	struct ubifs_info *c = priv;
+	struct ubifs_scan_node *sa, *sb;
+
+	cond_resched();
+	if (a == b)
+		return 0;
+
+	sa = list_entry(a, struct ubifs_scan_node, list);
+	sb = list_entry(b, struct ubifs_scan_node, list);
+
+	ubifs_assert(c, key_type(c, &sa->key) == UBIFS_DATA_KEY);
+	ubifs_assert(c, key_type(c, &sb->key) == UBIFS_DATA_KEY);
+	ubifs_assert(c, sa->type == UBIFS_DATA_NODE);
+	ubifs_assert(c, sb->type == UBIFS_DATA_NODE);
+
+	inuma = key_inum(c, &sa->key);
+	inumb = key_inum(c, &sb->key);
+
+	if (inuma == inumb) {
+		unsigned int blka = key_block(c, &sa->key);
+		unsigned int blkb = key_block(c, &sb->key);
+
+		if (blka <= blkb)
+			return -1;
+	} else if (inuma <= inumb)
+		return -1;
+
+	return 1;
+}
+
+/*
+ * nondata_nodes_cmp - compare 2 non-data nodes.
+ * @priv: UBIFS file-system description object
+ * @a: first node
+ * @a: second node
+ *
+ * This function compares nodes @a and @b. It makes sure that inode nodes go
+ * first and sorted by length in descending order. Directory entry nodes go
+ * after inode nodes and are sorted in ascending hash valuer order.
+ */
+static int nondata_nodes_cmp(void *priv, const struct list_head *a,
+			     const struct list_head *b)
+{
+	ino_t inuma, inumb;
+	struct ubifs_info *c = priv;
+	struct ubifs_scan_node *sa, *sb;
+
+	cond_resched();
+	if (a == b)
+		return 0;
+
+	sa = list_entry(a, struct ubifs_scan_node, list);
+	sb = list_entry(b, struct ubifs_scan_node, list);
+
+	ubifs_assert(c, key_type(c, &sa->key) != UBIFS_DATA_KEY &&
+		     key_type(c, &sb->key) != UBIFS_DATA_KEY);
+	ubifs_assert(c, sa->type != UBIFS_DATA_NODE &&
+		     sb->type != UBIFS_DATA_NODE);
+
+	/* Inodes go before directory entries */
+	if (sa->type == UBIFS_INO_NODE) {
+		if (sb->type == UBIFS_INO_NODE)
+			return sb->len - sa->len;
+		return -1;
+	}
+	if (sb->type == UBIFS_INO_NODE)
+		return 1;
+
+	ubifs_assert(c, key_type(c, &sa->key) == UBIFS_DENT_KEY ||
+		     key_type(c, &sa->key) == UBIFS_XENT_KEY);
+	ubifs_assert(c, key_type(c, &sb->key) == UBIFS_DENT_KEY ||
+		     key_type(c, &sb->key) == UBIFS_XENT_KEY);
+	ubifs_assert(c, sa->type == UBIFS_DENT_NODE ||
+		     sa->type == UBIFS_XENT_NODE);
+	ubifs_assert(c, sb->type == UBIFS_DENT_NODE ||
+		     sb->type == UBIFS_XENT_NODE);
+
+	inuma = key_inum(c, &sa->key);
+	inumb = key_inum(c, &sb->key);
+
+	if (inuma == inumb) {
+		uint32_t hasha = key_hash(c, &sa->key);
+		uint32_t hashb = key_hash(c, &sb->key);
+
+		if (hasha <= hashb)
+			return -1;
+	} else if (inuma <= inumb)
+		return -1;
+
+	return 1;
+}
+
+/**
+ * sort_nodes - sort nodes for GC.
+ * @c: UBIFS file-system description object
+ * @sleb: describes nodes to sort and contains the result on exit
+ * @nondata: contains non-data nodes on exit
+ * @min: minimum node size is returned here
+ *
+ * This function sorts the list of inodes to garbage collect. First of all, it
+ * kills obsolete nodes and separates data and non-data nodes to the
+ * @sleb->nodes and @nondata lists correspondingly.
+ *
+ * Data nodes are then sorted in block number order - this is important for
+ * bulk-read; data nodes with lower inode number go before data nodes with
+ * higher inode number, and data nodes with lower block number go before data
+ * nodes with higher block number;
+ *
+ * Non-data nodes are sorted as follows.
+ *   o First go inode nodes - they are sorted in descending length order.
+ *   o Then go directory entry nodes - they are sorted in hash order, which
+ *     should supposedly optimize 'readdir()'. Direntry nodes with lower parent
+ *     inode number go before direntry nodes with higher parent inode number,
+ *     and direntry nodes with lower name hash values go before direntry nodes
+ *     with higher name hash values.
+ *
+ * This function returns zero in case of success and a negative error code in
+ * case of failure.
+ */
+static int sort_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
+		      struct list_head *nondata, int *min)
+{
+	int err;
+	struct ubifs_scan_node *snod, *tmp;
+
+	*min = INT_MAX;
+
+	/* Separate data nodes and non-data nodes */
+	list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
+		ubifs_assert(c, snod->type == UBIFS_INO_NODE  ||
+			     snod->type == UBIFS_DATA_NODE ||
+			     snod->type == UBIFS_DENT_NODE ||
+			     snod->type == UBIFS_XENT_NODE ||
+			     snod->type == UBIFS_TRUN_NODE ||
+			     snod->type == UBIFS_AUTH_NODE);
+
+		if (snod->type != UBIFS_INO_NODE  &&
+		    snod->type != UBIFS_DATA_NODE &&
+		    snod->type != UBIFS_DENT_NODE &&
+		    snod->type != UBIFS_XENT_NODE) {
+			/* Probably truncation node, zap it */
+			list_del(&snod->list);
+			kfree(snod);
+			continue;
+		}
+
+		ubifs_assert(c, key_type(c, &snod->key) == UBIFS_DATA_KEY ||
+			     key_type(c, &snod->key) == UBIFS_INO_KEY  ||
+			     key_type(c, &snod->key) == UBIFS_DENT_KEY ||
+			     key_type(c, &snod->key) == UBIFS_XENT_KEY);
+
+		err = ubifs_tnc_has_node(c, &snod->key, 0, sleb->lnum,
+					 snod->offs, 0);
+		if (err < 0)
+			return err;
+
+		if (!err) {
+			/* The node is obsolete, remove it from the list */
+			list_del(&snod->list);
+			kfree(snod);
+			continue;
+		}
+
+		if (snod->len < *min)
+			*min = snod->len;
+
+		if (key_type(c, &snod->key) != UBIFS_DATA_KEY)
+			list_move_tail(&snod->list, nondata);
+	}
+
+	/* Sort data and non-data nodes */
+	list_sort(c, &sleb->nodes, &data_nodes_cmp);
+	list_sort(c, nondata, &nondata_nodes_cmp);
+
+	err = dbg_check_data_nodes_order(c, &sleb->nodes);
+	if (err)
+		return err;
+	err = dbg_check_nondata_nodes_order(c, nondata);
+	if (err)
+		return err;
+	return 0;
+}
+
+/**
+ * move_node - move a node.
+ * @c: UBIFS file-system description object
+ * @sleb: describes the LEB to move nodes from
+ * @snod: the mode to move
+ * @wbuf: write-buffer to move node to
+ *
+ * This function moves node @snod to @wbuf, changes TNC correspondingly, and
+ * destroys @snod. Returns zero in case of success and a negative error code in
+ * case of failure.
+ */
+static int move_node(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
+		     struct ubifs_scan_node *snod, struct ubifs_wbuf *wbuf)
+{
+	int err, new_lnum = wbuf->lnum, new_offs = wbuf->offs + wbuf->used;
+
+	cond_resched();
+	err = ubifs_wbuf_write_nolock(wbuf, snod->node, snod->len);
+	if (err)
+		return err;
+
+	err = ubifs_tnc_replace(c, &snod->key, sleb->lnum,
+				snod->offs, new_lnum, new_offs,
+				snod->len);
+	list_del(&snod->list);
+	kfree(snod);
+	return err;
+}
+
+/**
+ * move_nodes - move nodes.
+ * @c: UBIFS file-system description object
+ * @sleb: describes the LEB to move nodes from
+ *
+ * This function moves valid nodes from data LEB described by @sleb to the GC
+ * journal head. This function returns zero in case of success, %-EAGAIN if
+ * commit is required, and other negative error codes in case of other
+ * failures.
+ */
+static int move_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb)
+{
+	int err, min;
+	LIST_HEAD(nondata);
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+
+	if (wbuf->lnum == -1) {
+		/*
+		 * The GC journal head is not set, because it is the first GC
+		 * invocation since mount.
+		 */
+		err = switch_gc_head(c);
+		if (err)
+			return err;
+	}
+
+	err = sort_nodes(c, sleb, &nondata, &min);
+	if (err)
+		goto out;
+
+	/* Write nodes to their new location. Use the first-fit strategy */
+	while (1) {
+		int avail, moved = 0;
+		struct ubifs_scan_node *snod, *tmp;
+
+		/* Move data nodes */
+		list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
+			avail = c->leb_size - wbuf->offs - wbuf->used -
+					ubifs_auth_node_sz(c);
+			if  (snod->len > avail)
+				/*
+				 * Do not skip data nodes in order to optimize
+				 * bulk-read.
+				 */
+				break;
+
+			err = ubifs_shash_update(c, c->jheads[GCHD].log_hash,
+						 snod->node, snod->len);
+			if (err)
+				goto out;
+
+			err = move_node(c, sleb, snod, wbuf);
+			if (err)
+				goto out;
+			moved = 1;
+		}
+
+		/* Move non-data nodes */
+		list_for_each_entry_safe(snod, tmp, &nondata, list) {
+			avail = c->leb_size - wbuf->offs - wbuf->used -
+					ubifs_auth_node_sz(c);
+			if (avail < min)
+				break;
+
+			if  (snod->len > avail) {
+				/*
+				 * Keep going only if this is an inode with
+				 * some data. Otherwise stop and switch the GC
+				 * head. IOW, we assume that data-less inode
+				 * nodes and direntry nodes are roughly of the
+				 * same size.
+				 */
+				if (key_type(c, &snod->key) == UBIFS_DENT_KEY ||
+				    snod->len == UBIFS_INO_NODE_SZ)
+					break;
+				continue;
+			}
+
+			err = ubifs_shash_update(c, c->jheads[GCHD].log_hash,
+						 snod->node, snod->len);
+			if (err)
+				goto out;
+
+			err = move_node(c, sleb, snod, wbuf);
+			if (err)
+				goto out;
+			moved = 1;
+		}
+
+		if (ubifs_authenticated(c) && moved) {
+			struct ubifs_auth_node *auth;
+
+			auth = kmalloc(ubifs_auth_node_sz(c), GFP_NOFS);
+			if (!auth) {
+				err = -ENOMEM;
+				goto out;
+			}
+
+			err = ubifs_prepare_auth_node(c, auth,
+						c->jheads[GCHD].log_hash);
+			if (err) {
+				kfree(auth);
+				goto out;
+			}
+
+			err = ubifs_wbuf_write_nolock(wbuf, auth,
+						      ubifs_auth_node_sz(c));
+			if (err) {
+				kfree(auth);
+				goto out;
+			}
+
+			ubifs_add_dirt(c, wbuf->lnum, ubifs_auth_node_sz(c));
+		}
+
+		if (list_empty(&sleb->nodes) && list_empty(&nondata))
+			break;
+
+		/*
+		 * Waste the rest of the space in the LEB and switch to the
+		 * next LEB.
+		 */
+		err = switch_gc_head(c);
+		if (err)
+			goto out;
+	}
+
+	return 0;
+
+out:
+	list_splice_tail(&nondata, &sleb->nodes);
+	return err;
+}
+
+/**
+ * gc_sync_wbufs - sync write-buffers for GC.
+ * @c: UBIFS file-system description object
+ *
+ * We must guarantee that obsoleting nodes are on flash. Unfortunately they may
+ * be in a write-buffer instead. That is, a node could be written to a
+ * write-buffer, obsoleting another node in a LEB that is GC'd. If that LEB is
+ * erased before the write-buffer is sync'd and then there is an unclean
+ * unmount, then an existing node is lost. To avoid this, we sync all
+ * write-buffers.
+ *
+ * This function returns %0 on success or a negative error code on failure.
+ */
+static int gc_sync_wbufs(struct ubifs_info *c)
+{
+	int err, i;
+
+	for (i = 0; i < c->jhead_cnt; i++) {
+		if (i == GCHD)
+			continue;
+		err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+/**
+ * ubifs_garbage_collect_leb - garbage-collect a logical eraseblock.
+ * @c: UBIFS file-system description object
+ * @lp: describes the LEB to garbage collect
+ *
+ * This function garbage-collects an LEB and returns one of the @LEB_FREED,
+ * @LEB_RETAINED, etc positive codes in case of success, %-EAGAIN if commit is
+ * required, and other negative error codes in case of failures.
+ */
+int ubifs_garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp)
+{
+	struct ubifs_scan_leb *sleb;
+	struct ubifs_scan_node *snod;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+	int err = 0, lnum = lp->lnum;
+
+	ubifs_assert(c, c->gc_lnum != -1 || wbuf->offs + wbuf->used == 0 ||
+		     c->need_recovery);
+	ubifs_assert(c, c->gc_lnum != lnum);
+	ubifs_assert(c, wbuf->lnum != lnum);
+
+	if (lp->free + lp->dirty == c->leb_size) {
+		/* Special case - a free LEB  */
+		dbg_gc("LEB %d is free, return it", lp->lnum);
+		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
+
+		if (lp->free != c->leb_size) {
+			/*
+			 * Write buffers must be sync'd before unmapping
+			 * freeable LEBs, because one of them may contain data
+			 * which obsoletes something in 'lp->lnum'.
+			 */
+			err = gc_sync_wbufs(c);
+			if (err)
+				return err;
+			err = ubifs_change_one_lp(c, lp->lnum, c->leb_size,
+						  0, 0, 0, 0);
+			if (err)
+				return err;
+		}
+		err = ubifs_leb_unmap(c, lp->lnum);
+		if (err)
+			return err;
+
+		if (c->gc_lnum == -1) {
+			c->gc_lnum = lnum;
+			return LEB_RETAINED;
+		}
+
+		return LEB_FREED;
+	}
+
+	/*
+	 * We scan the entire LEB even though we only really need to scan up to
+	 * (c->leb_size - lp->free).
+	 */
+	sleb = ubifs_scan(c, lnum, 0, c->sbuf, 0);
+	if (IS_ERR(sleb))
+		return PTR_ERR(sleb);
+
+	ubifs_assert(c, !list_empty(&sleb->nodes));
+	snod = list_entry(sleb->nodes.next, struct ubifs_scan_node, list);
+
+	if (snod->type == UBIFS_IDX_NODE) {
+		struct ubifs_gced_idx_leb *idx_gc;
+
+		dbg_gc("indexing LEB %d (free %d, dirty %d)",
+		       lnum, lp->free, lp->dirty);
+		list_for_each_entry(snod, &sleb->nodes, list) {
+			struct ubifs_idx_node *idx = snod->node;
+			int level = le16_to_cpu(idx->level);
+
+			ubifs_assert(c, snod->type == UBIFS_IDX_NODE);
+			key_read(c, ubifs_idx_key(c, idx), &snod->key);
+			err = ubifs_dirty_idx_node(c, &snod->key, level, lnum,
+						   snod->offs);
+			if (err)
+				goto out;
+		}
+
+		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
+		if (!idx_gc) {
+			err = -ENOMEM;
+			goto out;
+		}
+
+		idx_gc->lnum = lnum;
+		idx_gc->unmap = 0;
+		list_add(&idx_gc->list, &c->idx_gc);
+
+		/*
+		 * Don't release the LEB until after the next commit, because
+		 * it may contain data which is needed for recovery. So
+		 * although we freed this LEB, it will become usable only after
+		 * the commit.
+		 */
+		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0,
+					  LPROPS_INDEX, 1);
+		if (err)
+			goto out;
+		err = LEB_FREED_IDX;
+	} else {
+		dbg_gc("data LEB %d (free %d, dirty %d)",
+		       lnum, lp->free, lp->dirty);
+
+		err = move_nodes(c, sleb);
+		if (err)
+			goto out_inc_seq;
+
+		err = gc_sync_wbufs(c);
+		if (err)
+			goto out_inc_seq;
+
+		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0, 0, 0);
+		if (err)
+			goto out_inc_seq;
+
+		/* Allow for races with TNC */
+		c->gced_lnum = lnum;
+		smp_wmb();
+		c->gc_seq += 1;
+		smp_wmb();
+
+		if (c->gc_lnum == -1) {
+			c->gc_lnum = lnum;
+			err = LEB_RETAINED;
+		} else {
+			err = ubifs_wbuf_sync_nolock(wbuf);
+			if (err)
+				goto out;
+
+			err = ubifs_leb_unmap(c, lnum);
+			if (err)
+				goto out;
+
+			err = LEB_FREED;
+		}
+	}
+
+out:
+	ubifs_scan_destroy(sleb);
+	return err;
+
+out_inc_seq:
+	/* We may have moved at least some nodes so allow for races with TNC */
+	c->gced_lnum = lnum;
+	smp_wmb();
+	c->gc_seq += 1;
+	smp_wmb();
+	goto out;
+}
+
+/**
+ * ubifs_garbage_collect - UBIFS garbage collector.
+ * @c: UBIFS file-system description object
+ * @anyway: do GC even if there are free LEBs
+ *
+ * This function does out-of-place garbage collection. The return codes are:
+ *   o positive LEB number if the LEB has been freed and may be used;
+ *   o %-EAGAIN if the caller has to run commit;
+ *   o %-ENOSPC if GC failed to make any progress;
+ *   o other negative error codes in case of other errors.
+ *
+ * Garbage collector writes data to the journal when GC'ing data LEBs, and just
+ * marking indexing nodes dirty when GC'ing indexing LEBs. Thus, at some point
+ * commit may be required. But commit cannot be run from inside GC, because the
+ * caller might be holding the commit lock, so %-EAGAIN is returned instead;
+ * And this error code means that the caller has to run commit, and re-run GC
+ * if there is still no free space.
+ *
+ * There are many reasons why this function may return %-EAGAIN:
+ * o the log is full and there is no space to write an LEB reference for
+ *   @c->gc_lnum;
+ * o the journal is too large and exceeds size limitations;
+ * o GC moved indexing LEBs, but they can be used only after the commit;
+ * o the shrinker fails to find clean znodes to free and requests the commit;
+ * o etc.
+ *
+ * Note, if the file-system is close to be full, this function may return
+ * %-EAGAIN infinitely, so the caller has to limit amount of re-invocations of
+ * the function. E.g., this happens if the limits on the journal size are too
+ * tough and GC writes too much to the journal before an LEB is freed. This
+ * might also mean that the journal is too large, and the TNC becomes to big,
+ * so that the shrinker is constantly called, finds not clean znodes to free,
+ * and requests commit. Well, this may also happen if the journal is all right,
+ * but another kernel process consumes too much memory. Anyway, infinite
+ * %-EAGAIN may happen, but in some extreme/misconfiguration cases.
+ */
+int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
+{
+	int i, err, ret, min_space = c->dead_wm;
+	struct ubifs_lprops lp;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+
+	ubifs_assert_cmt_locked(c);
+	ubifs_assert(c, !c->ro_media && !c->ro_mount);
+
+	if (ubifs_gc_should_commit(c))
+		return -EAGAIN;
+
+	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+
+	if (c->ro_error) {
+		ret = -EROFS;
+		goto out_unlock;
+	}
+
+	/* We expect the write-buffer to be empty on entry */
+	ubifs_assert(c, !wbuf->used);
+
+	for (i = 0; ; i++) {
+		int space_before, space_after;
+
+		/* Maybe continue after find and break before find */
+		lp.lnum = -1;
+
+		cond_resched();
+
+		/* Give the commit an opportunity to run */
+		if (ubifs_gc_should_commit(c)) {
+			ret = -EAGAIN;
+			break;
+		}
+
+		if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
+			/*
+			 * We've done enough iterations. Indexing LEBs were
+			 * moved and will be available after the commit.
+			 */
+			dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
+			ubifs_commit_required(c);
+			ret = -EAGAIN;
+			break;
+		}
+
+		if (i > HARD_LEBS_LIMIT) {
+			/*
+			 * We've moved too many LEBs and have not made
+			 * progress, give up.
+			 */
+			dbg_gc("hard limit, -ENOSPC");
+			ret = -ENOSPC;
+			break;
+		}
+
+		/*
+		 * Empty and freeable LEBs can turn up while we waited for
+		 * the wbuf lock, or while we have been running GC. In that
+		 * case, we should just return one of those instead of
+		 * continuing to GC dirty LEBs. Hence we request
+		 * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
+		 */
+		ret = ubifs_find_dirty_leb(c, &lp, min_space, anyway ? 0 : 1);
+		if (ret) {
+			if (ret == -ENOSPC)
+				dbg_gc("no more dirty LEBs");
+			break;
+		}
+
+		dbg_gc("found LEB %d: free %d, dirty %d, sum %d (min. space %d)",
+		       lp.lnum, lp.free, lp.dirty, lp.free + lp.dirty,
+		       min_space);
+
+		space_before = c->leb_size - wbuf->offs - wbuf->used;
+		if (wbuf->lnum == -1)
+			space_before = 0;
+
+		ret = ubifs_garbage_collect_leb(c, &lp);
+		if (ret < 0) {
+			if (ret == -EAGAIN) {
+				/*
+				 * This is not error, so we have to return the
+				 * LEB to lprops. But if 'ubifs_return_leb()'
+				 * fails, its failure code is propagated to the
+				 * caller instead of the original '-EAGAIN'.
+				 */
+				err = ubifs_return_leb(c, lp.lnum);
+				if (err) {
+					ret = err;
+					/*
+					 * An LEB may always be "taken",
+					 * so setting ubifs to read-only,
+					 * and then executing sync wbuf will
+					 * return -EROFS and enter the "out"
+					 * error branch.
+					 */
+					ubifs_ro_mode(c, ret);
+				}
+				/*  Maybe double return LEB if goto out */
+				lp.lnum = -1;
+				break;
+			}
+			goto out;
+		}
+
+		if (ret == LEB_FREED) {
+			/* An LEB has been freed and is ready for use */
+			dbg_gc("LEB %d freed, return", lp.lnum);
+			ret = lp.lnum;
+			break;
+		}
+
+		if (ret == LEB_FREED_IDX) {
+			/*
+			 * This was an indexing LEB and it cannot be
+			 * immediately used. And instead of requesting the
+			 * commit straight away, we try to garbage collect some
+			 * more.
+			 */
+			dbg_gc("indexing LEB %d freed, continue", lp.lnum);
+			continue;
+		}
+
+		ubifs_assert(c, ret == LEB_RETAINED);
+		space_after = c->leb_size - wbuf->offs - wbuf->used;
+		dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
+		       space_after - space_before);
+
+		if (space_after > space_before) {
+			/* GC makes progress, keep working */
+			min_space >>= 1;
+			if (min_space < c->dead_wm)
+				min_space = c->dead_wm;
+			continue;
+		}
+
+		dbg_gc("did not make progress");
+
+		/*
+		 * GC moved an LEB bud have not done any progress. This means
+		 * that the previous GC head LEB contained too few free space
+		 * and the LEB which was GC'ed contained only large nodes which
+		 * did not fit that space.
+		 *
+		 * We can do 2 things:
+		 * 1. pick another LEB in a hope it'll contain a small node
+		 *    which will fit the space we have at the end of current GC
+		 *    head LEB, but there is no guarantee, so we try this out
+		 *    unless we have already been working for too long;
+		 * 2. request an LEB with more dirty space, which will force
+		 *    'ubifs_find_dirty_leb()' to start scanning the lprops
+		 *    table, instead of just picking one from the heap
+		 *    (previously it already picked the dirtiest LEB).
+		 */
+		if (i < SOFT_LEBS_LIMIT) {
+			dbg_gc("try again");
+			continue;
+		}
+
+		min_space <<= 1;
+		if (min_space > c->dark_wm)
+			min_space = c->dark_wm;
+		dbg_gc("set min. space to %d", min_space);
+	}
+
+	if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
+		dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
+		ubifs_commit_required(c);
+		ret = -EAGAIN;
+	}
+
+	err = ubifs_wbuf_sync_nolock(wbuf);
+	if (!err)
+		err = ubifs_leb_unmap(c, c->gc_lnum);
+	if (err) {
+		ret = err;
+		goto out;
+	}
+out_unlock:
+	mutex_unlock(&wbuf->io_mutex);
+	return ret;
+
+out:
+	ubifs_assert(c, ret < 0);
+	ubifs_assert(c, ret != -ENOSPC && ret != -EAGAIN);
+	ubifs_wbuf_sync_nolock(wbuf);
+	ubifs_ro_mode(c, ret);
+	mutex_unlock(&wbuf->io_mutex);
+	if (lp.lnum != -1)
+		ubifs_return_leb(c, lp.lnum);
+	return ret;
+}
+
+/**
+ * ubifs_gc_start_commit - garbage collection at start of commit.
+ * @c: UBIFS file-system description object
+ *
+ * If a LEB has only dirty and free space, then we may safely unmap it and make
+ * it free.  Note, we cannot do this with indexing LEBs because dirty space may
+ * correspond index nodes that are required for recovery.  In that case, the
+ * LEB cannot be unmapped until after the next commit.
+ *
+ * This function returns %0 upon success and a negative error code upon failure.
+ */
+int ubifs_gc_start_commit(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc;
+	const struct ubifs_lprops *lp;
+	int err = 0, flags;
+
+	ubifs_get_lprops(c);
+
+	/*
+	 * Unmap (non-index) freeable LEBs. Note that recovery requires that all
+	 * wbufs are sync'd before this, which is done in 'do_commit()'.
+	 */
+	while (1) {
+		lp = ubifs_fast_find_freeable(c);
+		if (!lp)
+			break;
+		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
+		err = ubifs_leb_unmap(c, lp->lnum);
+		if (err)
+			goto out;
+		lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
+		if (IS_ERR(lp)) {
+			err = PTR_ERR(lp);
+			goto out;
+		}
+		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
+	}
+
+	/* Mark GC'd index LEBs OK to unmap after this commit finishes */
+	list_for_each_entry(idx_gc, &c->idx_gc, list)
+		idx_gc->unmap = 1;
+
+	/* Record index freeable LEBs for unmapping after commit */
+	while (1) {
+		lp = ubifs_fast_find_frdi_idx(c);
+		if (IS_ERR(lp)) {
+			err = PTR_ERR(lp);
+			goto out;
+		}
+		if (!lp)
+			break;
+		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
+		if (!idx_gc) {
+			err = -ENOMEM;
+			goto out;
+		}
+		ubifs_assert(c, !(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(c, lp->flags & LPROPS_INDEX);
+		/* Don't release the LEB until after the next commit */
+		flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
+		lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
+		if (IS_ERR(lp)) {
+			err = PTR_ERR(lp);
+			kfree(idx_gc);
+			goto out;
+		}
+		ubifs_assert(c, lp->flags & LPROPS_TAKEN);
+		ubifs_assert(c, !(lp->flags & LPROPS_INDEX));
+		idx_gc->lnum = lp->lnum;
+		idx_gc->unmap = 1;
+		list_add(&idx_gc->list, &c->idx_gc);
+	}
+out:
+	ubifs_release_lprops(c);
+	return err;
+}
+
+/**
+ * ubifs_gc_end_commit - garbage collection at end of commit.
+ * @c: UBIFS file-system description object
+ *
+ * This function completes out-of-place garbage collection of index LEBs.
+ */
+int ubifs_gc_end_commit(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc, *tmp;
+	struct ubifs_wbuf *wbuf;
+	int err = 0;
+
+	wbuf = &c->jheads[GCHD].wbuf;
+	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+	list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
+		if (idx_gc->unmap) {
+			dbg_gc("LEB %d", idx_gc->lnum);
+			err = ubifs_leb_unmap(c, idx_gc->lnum);
+			if (err)
+				goto out;
+			err = ubifs_change_one_lp(c, idx_gc->lnum, LPROPS_NC,
+					  LPROPS_NC, 0, LPROPS_TAKEN, -1);
+			if (err)
+				goto out;
+			list_del(&idx_gc->list);
+			kfree(idx_gc);
+		}
+out:
+	mutex_unlock(&wbuf->io_mutex);
+	return err;
+}
+
+/**
+ * ubifs_destroy_idx_gc - destroy idx_gc list.
+ * @c: UBIFS file-system description object
+ *
+ * This function destroys the @c->idx_gc list. It is called when unmounting
+ * so locks are not needed. Returns zero in case of success and a negative
+ * error code in case of failure.
+ */
+void ubifs_destroy_idx_gc(struct ubifs_info *c)
+{
+	while (!list_empty(&c->idx_gc)) {
+		struct ubifs_gced_idx_leb *idx_gc;
+
+		idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
+				    list);
+		c->idx_gc_cnt -= 1;
+		list_del(&idx_gc->list);
+		kfree(idx_gc);
+	}
+}
+
+/**
+ * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
+ * @c: UBIFS file-system description object
+ *
+ * Called during start commit so locks are not needed.
+ */
+int ubifs_get_idx_gc_leb(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc;
+	int lnum;
+
+	if (list_empty(&c->idx_gc))
+		return -ENOSPC;
+	idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
+	lnum = idx_gc->lnum;
+	/* c->idx_gc_cnt is updated by the caller when lprops are updated */
+	list_del(&idx_gc->list);
+	kfree(idx_gc);
+	return lnum;
+}