[Qemu-devel] [PATCH v2 3/4] raw-posix: Fix try_seek_hole()'s handling of SEEK_DATA failure

[Markus Armbruster <armbru@redhat.com>]

When SEEK_HOLE tells us we're in a hole, we try SEEK_DATA to find its
end.  When that fails, we pretend the hole extends to the end of file.
Wrong.  Except when SEEK_END fails, we screw up and claim it extends
to offset -1.  More wrong.

Fortunately, these seeks are very unlikely to fail.  Fix it anyway, by
returning failure.  The caller will then pretend there are no holes.
Inaccurate, but safe.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 block/raw-posix.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index fd80d84..2a12a50 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -1494,8 +1494,9 @@ static int try_seek_hole(BlockDriverState *bs, off_t start, off_t *data,
     } else {
         /* On a hole.  We need another syscall to find its end.  */
         *data = lseek(s->fd, start, SEEK_DATA);
-        if (*data == -1) {
-            *data = lseek(s->fd, 0, SEEK_END);
+        if (*data < 0) {
+            /* no idea where the hole ends, give up (unlikely to happen) */
+            return -errno;
         }
     }
 
-- 
1.9.3