In some cases like small FSes with no meta_bg and where the resize doesn't
need extra gdt blocks as it can fit in the current one,
s_reserved_gdt_blocks is set as 0, which causes fsmap to emit a 0 length
entry, which is incorrect.
$ mkfs.ext4 -b 65536 -O bigalloc /dev/sda 5G
$ mount /dev/sda /mnt/scratch
$ xfs_io -c "fsmap -d" /mnt/scartch
0: 253:48 [0..127]: static fs metadata 128
1: 253:48 [128..255]: special 102:1 128
2: 253:48 [256..255]: special 102:2 0 <---- 0 len entry
3: 253:48 [256..383]: special 102:3 128
Fix this by adding a check for this case.
Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls")
Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
---
fs/ext4/fsmap.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
index 9d63c39f6077..91185c40f755 100644
--- a/fs/ext4/fsmap.c
+++ b/fs/ext4/fsmap.c
@@ -393,6 +393,14 @@ static unsigned int ext4_getfsmap_find_sb(struct super_block *sb,
/* Reserved GDT blocks */
if (!ext4_has_feature_meta_bg(sb) || metagroup < first_meta_bg) {
len = le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
+
+ /*
+ * mkfs.ext4 can set s_reserved_gdt_blocks as 0 in some cases,
+ * check for that.
+ */
+ if (!len)
+ return 0;
+
error = ext4_getfsmap_fill(meta_list, fsb, len,
EXT4_FMR_OWN_RESV_GDT);
if (error)
--
2.49.0
