On 7/26/20 10:25 AM, Nir Soffer wrote:
When converting to qcow2 compressed format, the last step is a special
zero length compressed write, ending in call to bdrv_co_truncate(). This
call always fail for the nbd driver since it does not implement
fails
bdrv_co_truncate().
Arguably, qemu-img should be taught to ignore the failure, since it is
not unique to the nbd driver. But I can live with your approach here.
For block devices, which have the same limits, the call succeeds since
file driver implements bdrv_co_truncate(). If the caller asked to
truncate to the same or smaller size with exact=false, the truncate
succeeds. Implement the same logic for nbd.
Example failing without this change:
Fixes: https://bugzilla.redhat.com/1860627
Signed-off-by: Nir Soffer <nsof...@redhat.com>
---
block/nbd.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/block/nbd.c b/block/nbd.c
index 65a4f56924..2154113af3 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -1966,6 +1966,30 @@ static void nbd_close(BlockDriverState *bs)
nbd_clear_bdrvstate(s);
}
+/*
+ * NBD cannot truncate, but if the caller ask to truncate to the same size, or
asks
+ * to a smaller size with extact=false, there is not reason to fail the
exact, no
+ * operation.
+ */
+static int coroutine_fn nbd_co_truncate(BlockDriverState *bs, int64_t offset,
+ bool exact, PreallocMode prealloc,
+ BdrvRequestFlags flags, Error **errp)
+{
+ BDRVNBDState *s = bs->opaque;
+
+ if (offset != s->info.size && exact) {
+ error_setg(errp, "Cannot resize NBD nodes");
+ return -ENOTSUP;
+ }
+
+ if (offset > s->info.size) {
+ error_setg(errp, "Cannot grow NBD nodes");
+ return -EINVAL;
+ }
+
+ return 0;
Looks reasonable. As Max said, I wonder if we want to reject particular
preallocation modes (looking at block/file-posix.c:raw_co_truncate), in
the case where the image was resized down and then back up (since
s->info.size is constant, but the BDS size is not if inexact resize
succeeds).
As you have a bugzilla entry, I think this is safe for -rc2; I'll be
touching up the typos and queuing it through my NBD tree later today.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
