[PATCH v3 2/3] exfat: retain the next empty directory entry hint

[Yang Wen]

After a Bloom filter miss skips the name scan, finding an empty entry can
still rescan the directory from the beginning.

Advance the empty-entry hint past each newly allocated entry set and retain
it while the name filter is active. Invalidate the hint whenever create
rollback, unlink, rmdir, rename, or move can free entries, so the next
allocation rediscovers earlier holes.

This preserves the fast append path during bulk creation without allowing
stale hints to cause unbounded directory growth.

Signed-off-by: Yang Wen <anmuxixixi@xxxxxxxxx>
---
 fs/exfat/namei.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index 96f33226f2c0..56772167ba5d 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -199,6 +199,50 @@ const struct dentry_operations exfat_utf8_dentry_ops = {
 	.d_compare	= exfat_utf8_d_cmp,
 };
 
+static void exfat_set_next_empty_hint(struct inode *inode,
+				      struct exfat_chain *p_dir, int dentry,
+				      int num_entries,
+				      struct exfat_entry_set_cache *es)
+{
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+	struct exfat_sb_info *sbi = EXFAT_SB(inode->i_sb);
+	unsigned int next = dentry + num_entries;
+	unsigned int total = exfat_cluster_to_dentries(sbi, p_dir->size);
+	struct exfat_chain cur;
+
+	if (next >= total) {
+		exfat_chain_set(&ei->hint_femp.cur, EXFAT_EOF_CLUSTER, 0,
+				p_dir->flags);
+		ei->hint_femp.eidx = total;
+		ei->hint_femp.count = 0;
+		return;
+	}
+
+	cur.dir = exfat_sector_to_cluster(sbi,
+					  es->bh[es->num_bh - 1]->b_blocknr);
+	cur.flags = p_dir->flags;
+	cur.size = p_dir->size - exfat_dentries_to_cluster(sbi, next);
+	if (!(next & (sbi->dentries_per_clu - 1))) {
+		cur.size++;
+		if (exfat_chain_advance(inode->i_sb, &cur, 1)) {
+			ei->hint_femp.eidx = EXFAT_HINT_NONE;
+			return;
+		}
+	}
+
+	ei->hint_femp.cur = cur;
+	ei->hint_femp.eidx = next;
+	ei->hint_femp.count = 0;
+}
+
+static void exfat_invalidate_empty_hint(struct inode *inode)
+{
+	struct exfat_inode_info *ei = EXFAT_I(inode);
+
+	ei->hint_femp.eidx = EXFAT_HINT_NONE;
+	ei->hint_femp.count = 0;
+}
+
 /* search EMPTY CONTINUOUS "num_entries" entries */
 static int exfat_search_empty_slot(struct super_block *sb,
 		struct exfat_hint_femp *hint_femp, struct exfat_chain *p_dir,
@@ -385,6 +429,8 @@ int exfat_find_empty_entry(struct inode *inode,
 		inode->i_blocks += sbi->cluster_size >> 9;
 	}
 
+	exfat_set_next_empty_hint(inode, p_dir, dentry, num_entries, es);
+
 	p_dir->dir = exfat_sector_to_cluster(sbi, es->bh[0]->b_blocknr);
 	p_dir->size -= dentry / sbi->dentries_per_clu;
 
@@ -516,6 +562,7 @@ static int exfat_add_entry(struct inode *inode, const char *path,
 						   dentry, ES_ALL_ENTRIES);
 		if (!cleanup_ret) {
 			exfat_remove_entries(inode, &es, ES_IDX_FILE, false);
+			exfat_invalidate_empty_hint(inode);
 			cleanup_ret = exfat_put_dentry_set(&es,
 							   IS_DIRSYNC(inode));
 		}
@@ -628,7 +675,8 @@ static int exfat_find(struct inode *dir, const struct qstr *qname,
 		ei->hint_stat.clu = cdir.dir;
 		ei->hint_stat.eidx = 0;
 		ei->version = (inode_peek_iversion_raw(dir) & 0xffffffff);
-		ei->hint_femp.eidx = EXFAT_HINT_NONE;
+		if (!ei->name_filter)
+			ei->hint_femp.eidx = EXFAT_HINT_NONE;
 	}
 
 	/* search the file name for directories */
@@ -803,6 +851,8 @@ static int exfat_unlink(struct inode *dir, struct dentry *dentry)
 
 	/* update the directory entry */
 	exfat_remove_entries(inode, &es, ES_IDX_FILE, true);
+	exfat_invalidate_empty_hint(dir);
+
 	err = exfat_put_dentry_set(&es, IS_DIRSYNC(inode));
 	if (err)
 		goto unlock;
@@ -957,6 +1007,8 @@ static int exfat_rmdir(struct inode *dir, struct dentry *dentry)
 	exfat_set_volume_dirty(sb);
 
 	exfat_remove_entries(inode, &es, ES_IDX_FILE, true);
+	exfat_invalidate_empty_hint(dir);
+
 	err = exfat_put_dentry_set(&es, IS_DIRSYNC(dir));
 	if (err)
 		goto unlock;
@@ -1138,6 +1190,7 @@ static int exfat_move_file(struct inode *parent_inode,
 					  ES_ALL_ENTRIES)) {
 			exfat_remove_entries(parent_inode, &new_es,
 					    ES_IDX_FILE, false);
+			exfat_invalidate_empty_hint(parent_inode);
 			exfat_put_dentry_set(&new_es, false);
 		}
 		goto put_mov_es;
@@ -1214,6 +1267,7 @@ static int __exfat_rename(struct inode *old_parent_inode,
 		ret = exfat_rename_file(new_parent_inode, &uni_name, ei);
 	else
 		ret = exfat_move_file(new_parent_inode, &uni_name, ei);
+	exfat_invalidate_empty_hint(old_parent_inode);
 	if (!ret)
 		exfat_name_filter_add(new_parent_inode, &uni_name);
 
@@ -1228,6 +1282,8 @@ static int __exfat_rename(struct inode *old_parent_inode,
 		}
 
 		exfat_remove_entries(new_inode, &es, ES_IDX_FILE, true);
+		exfat_invalidate_empty_hint(new_parent_inode);
+
 		ret = exfat_put_dentry_set(&es, IS_DIRSYNC(new_inode));
 		if (ret)
 			goto del_out;
-- 
2.34.1