On current released versions of glusterfs, glfs_lseek() will sometimes
return invalid values for SEEK_DATA or SEEK_HOLE. For SEEK_DATA and
SEEK_HOLE, the returned value should be >= the passed offset, or < 0 in
the case of error:
LSEEK(2):
off_t lseek(int fd, off_t offset, int whence);
[...]
SEEK_HOLE
Adjust the file offset to the next hole in the file greater
than or equal to offset. If offset points into the middle of
a hole, then the file offset is set to offset. If there is no
hole past offset, then the file offset is adjusted to the end
of the file (i.e., there is an implicit hole at the end of
any file).
[...]
RETURN VALUE
Upon successful completion, lseek() returns the resulting
offset location as measured in bytes from the beginning of the
file. On error, the value (off_t) -1 is returned and errno is
set to indicate the error
However, occasionally glfs_lseek() for SEEK_HOLE/DATA will return a
value less than the passed offset, yet greater than zero.
For instance, here are example values observed from this call:
offs = glfs_lseek(s->fd, start, SEEK_HOLE);
if (offs < 0) {
return -errno; /* D1 and (H3 or H4) */
}
start == 7608336384
offs == 7607877632
This causes QEMU to abort on the assert test. When this value is
returned, errno is also 0.
This is a reported and known bug to glusterfs:
https://bugzilla.redhat.com/show_bug.cgi?id=1425293
Although this is being fixed in gluster, we still should work around it
in QEMU, given that multiple released versions of gluster behave this
way.
This patch treats the return case of (offs < start) the same as if an
error value other than ENXIO is returned; we will assume we learned
nothing, and there are no holes in the file.
Signed-off-by: Jeff Cody <jc...@redhat.com>
---
block/gluster.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/block/gluster.c b/block/gluster.c
index 7c76cd0..c147909e 100644
--- a/block/gluster.c
+++ b/block/gluster.c
@@ -1275,7 +1275,14 @@ static int find_allocation(BlockDriverState *bs, off_t
start,
if (offs < 0) {
return -errno; /* D3 or D4 */
}
- assert(offs >= start);
+
+ if (offs < start) {
+ /* This is not a valid return by lseek(). We are safe to just return
+ * -EIO in this case, and we'll treat it like D4. Unfortunately some
+ * versions of libgfapi will return offs < start, so an assert here
+ * will unneccesarily abort QEMU. */
+ return -EIO;
+ }
if (offs > start) {
/* D2: in hole, next data at offs */
@@ -1307,7 +1314,14 @@ static int find_allocation(BlockDriverState *bs, off_t
start,
if (offs < 0) {
return -errno; /* D1 and (H3 or H4) */
}
- assert(offs >= start);
+
+ if (offs < start) {
+ /* This is not a valid return by lseek(). We are safe to just return
+ * -EIO in this case, and we'll treat it like H4. Unfortunately some
+ * versions of libgfapi will return offs < start, so an assert here
+ * will unneccesarily abort QEMU. */
+ return -EIO;
+ }
if (offs > start) {
/*
--
2.9.3
