[PATCH v1 02/11] exfat: add exfat_get_empty_dentry_set() helper

[yuezhang.mo@foxmail.com]

From: Yuezhang Mo <Yuezhang.Mo@sony.com>

This helper is used to lookup empty dentry set. If there are
enough empty dentries at the input location, this helper will
return the number of dentries that need to be skipped for the
next lookup.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Andy Wu <Andy.Wu@sony.com>
Reviewed-by: Aoyama Wataru <wataru.aoyama@sony.com>
---
 fs/exfat/dir.c      | 77 +++++++++++++++++++++++++++++++++++++++++++++
 fs/exfat/exfat_fs.h |  3 ++
 2 files changed, 80 insertions(+)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index f33e40aad276..bb23585c6e7c 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -950,6 +950,83 @@ int exfat_get_dentry_set(struct exfat_entry_set_cache *es,
 	return -EIO;
 }
 
+static int exfat_validate_empty_dentry_set(struct exfat_entry_set_cache *es)
+{
+	struct exfat_dentry *ep;
+	struct buffer_head *bh;
+	int i, off;
+	bool unused_hit = false;
+
+	for (i = 0; i < es->num_entries; i++) {
+		ep = exfat_get_dentry_cached(es, i);
+		if (ep->type == EXFAT_UNUSED)
+			unused_hit = true;
+		else if (IS_EXFAT_DELETED(ep->type)) {
+			if (unused_hit)
+				goto out;
+		} else {
+			if (unused_hit)
+				goto out;
+
+			i++;
+			goto count_skip_entries;
+		}
+	}
+
+	return 0;
+
+out:
+	off = es->start_off + (i << DENTRY_SIZE_BITS);
+	bh = es->bh[EXFAT_B_TO_BLK(off, es->sb)];
+
+	exfat_fs_error(es->sb,
+		"in sector %lld, dentry %d should be unused, but 0x%x",
+		bh->b_blocknr, off >> DENTRY_SIZE_BITS, ep->type);
+
+	return -EIO;
+
+count_skip_entries:
+	es->num_entries = EXFAT_B_TO_DEN(EXFAT_BLK_TO_B(es->num_bh, es->sb) - es->start_off);
+	for (; i < es->num_entries; i++) {
+		ep = exfat_get_dentry_cached(es, i);
+		if (IS_EXFAT_DELETED(ep->type))
+			break;
+	}
+
+	return i;
+}
+
+/*
+ * Get an empty dentry set.
+ *
+ * in:
+ *   sb+p_dir+entry: indicates the empty dentry location
+ *   num_entries: specifies how many empty dentries should be included.
+ * out:
+ *   es: pointer of empty dentry set on success.
+ * return:
+ *   0   : on success
+ *   >= 0: the dentries are not empty, the return value is the number of
+ *         dentries to be skipped for the next lookup.
+ *   <0  : on failure
+ */
+int exfat_get_empty_dentry_set(struct exfat_entry_set_cache *es,
+		struct super_block *sb, struct exfat_chain *p_dir,
+		int entry, unsigned int num_entries)
+{
+	int ret;
+
+	ret = __exfat_get_dentry_set(es, sb, p_dir, entry, num_entries);
+	if (ret < 0)
+		return ret;
+
+	ret = exfat_validate_empty_dentry_set(es);
+	if (ret)
+		exfat_put_dentry_set(es, false);
+
+	return ret;
+}
+
 static inline void exfat_reset_empty_hint(struct exfat_hint_femp *hint_femp)
 {
 	hint_femp->eidx = EXFAT_HINT_NONE;
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index e3b1f8e022df..6dc76b3f4945 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -502,6 +502,9 @@ struct exfat_dentry *exfat_get_dentry_cached(struct exfat_entry_set_cache *es,
 int exfat_get_dentry_set(struct exfat_entry_set_cache *es,
 		struct super_block *sb, struct exfat_chain *p_dir, int entry,
 		unsigned int type);
+int exfat_get_empty_dentry_set(struct exfat_entry_set_cache *es,
+		struct super_block *sb, struct exfat_chain *p_dir, int entry,
+		unsigned int num_entries);
 int exfat_put_dentry_set(struct exfat_entry_set_cache *es, int sync);
 int exfat_count_dir_entries(struct super_block *sb, struct exfat_chain *p_dir);
 
-- 
2.25.1