@@ -1966,6 +1966,33 @@ static void nbd_close(BlockDriverState *bs)
nbd_clear_bdrvstate(s);
}
+/*
+ * NBD cannot truncate, but if the caller asks to truncate to the same size, or
+ * to a smaller size with exact=false, there is no reason to fail the
+ * operation.
+ *
+ * Preallocation mode is ignored since it does not seems useful to fail when
+ * when never change anything.
+ */
+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;
+}
+
static int64_t nbd_getlength(BlockDriverState *bs)
{
BDRVNBDState *s = bs->opaque;
@@ -2045,6 +2072,7 @@ static BlockDriver bdrv_nbd = {
.bdrv_co_flush_to_os = nbd_co_flush,
.bdrv_co_pdiscard = nbd_client_co_pdiscard,
.bdrv_refresh_limits = nbd_refresh_limits,
+ .bdrv_co_truncate = nbd_co_truncate,
.bdrv_getlength = nbd_getlength,
.bdrv_detach_aio_context = nbd_client_detach_aio_context,
.bdrv_attach_aio_context = nbd_client_attach_aio_context,
@@ -2072,6 +2100,7 @@ static BlockDriver bdrv_nbd_tcp = {
.bdrv_co_flush_to_os = nbd_co_flush,
.bdrv_co_pdiscard = nbd_client_co_pdiscard,
.bdrv_refresh_limits = nbd_refresh_limits,
+ .bdrv_co_truncate = nbd_co_truncate,
.bdrv_getlength = nbd_getlength,
.bdrv_detach_aio_context = nbd_client_detach_aio_context,
.bdrv_attach_aio_context = nbd_client_attach_aio_context,
@@ -2099,6 +2128,7 @@ static BlockDriver bdrv_nbd_unix = {
.bdrv_co_flush_to_os = nbd_co_flush,
.bdrv_co_pdiscard = nbd_client_co_pdiscard,
.bdrv_refresh_limits = nbd_refresh_limits,
+ .bdrv_co_truncate = nbd_co_truncate,
.bdrv_getlength = nbd_getlength,
.bdrv_detach_aio_context = nbd_client_detach_aio_context,
.bdrv_attach_aio_context = nbd_client_attach_aio_context,
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 fails for the nbd driver since it does not implement bdrv_co_truncate(). 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: In one shell starts qemu-nbd: $ truncate -s 1g test.tar $ qemu-nbd --socket=/tmp/nbd.sock --persistent --format=raw --offset 1536 test.tar In another shell convert an image to qcow2 compressed via NBD: $ echo "disk data" > disk.raw $ truncate -s 1g disk.raw $ qemu-img convert -f raw -O qcow2 -c disk1.raw nbd+unix:///?socket=/tmp/nbd.sock; echo $? 1 qemu-img failed, but the conversion was successful: $ qemu-img info nbd+unix:///?socket=/tmp/nbd.sock image: nbd+unix://?socket=/tmp/nbd.sock file format: qcow2 virtual size: 1 GiB (1073741824 bytes) ... $ qemu-img check nbd+unix:///?socket=/tmp/nbd.sock No errors were found on the image. 1/16384 = 0.01% allocated, 100.00% fragmented, 100.00% compressed clusters Image end offset: 393216 $ qemu-img compare disk.raw nbd+unix:///?socket=/tmp/nbd.sock Images are identical. Fixes: https://bugzilla.redhat.com/1860627 Signed-off-by: Nir Soffer <nsoffer@redhat.com> --- block/nbd.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)