I have a valid btrfs image which contains,
...
item 10 key (1103101952 BLOCK_GROUP_ITEM 1288372224) itemoff 15947 itemsize 24
block group used 655360 chunk_objectid 256 flags DATA|RAID5
item 11 key (1103364096 EXTENT_ITEM 131072) itemoff 15894 itemsize 53
extent refs 1 gen 11 flags DATA
extent data backref root 5 objectid 258 offset 0 count 1
item 12 key (1103888384 EXTENT_ITEM 262144) itemoff 15841 itemsize 53
extent refs 1 gen 15 flags DATA
extent data backref root 1 objectid 256 offset 0 count 1
item 13 key (1104281600 EXTENT_ITEM 262144) itemoff 15788 itemsize 53
extent refs 1 gen 15 flags DATA
extent data backref root 1 objectid 257 offset 0 count 1
...
The extent [1103364096, 131072) has length 131072, but if we run
"btrfs-map-logical -l 1103364096 -b $((65536 * 3)) /dev/sda"
it will return mapping info 's of non-existing extents.
It's because it assumes that extents's are contiguous on logical address,
when it's not true, after one loop (cur_logical += cur_len) and mapping
the next extent, we can get an extent that is out of our search range and
we end up with a negative @real_len and printing all mapping infos till
the disk end.
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
---
btrfs-map-logical.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/btrfs-map-logical.c b/btrfs-map-logical.c
index fd0286d..f421a50 100644
--- a/btrfs-map-logical.c
+++ b/btrfs-map-logical.c
@@ -329,6 +329,11 @@ int main(int argc, char **argv)
goto out_close_fd;
if (ret > 0)
break;
+ /* check again if there is overlap. */
+ if (cur_logical + cur_len < logical ||
+ cur_logical >= logical + bytes)
+ break;
+
real_logical = max(logical, cur_logical);
real_len = min(logical + bytes, cur_logical + cur_len) -
real_logical;
--
2.5.0
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