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block: nbd: Fix convert qcow2 compressed to nbd

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When converting to qcow2 compressed format, the last step is a special
zero length compressed write, ending in a 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
the 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 start 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>
Message-Id: <20200727215846.395443-2-nsoffer@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
[eblake: typo fixes]
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Nir Soffer 2020-07-28 00:58:43 +03:00 committed by Eric Blake
parent 890cbccb08
commit a2b333c018
2 changed files with 31 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
block/nbd.c
View File

@ -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
* we 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,

2
qemu-io-cmds.c
View File

@ -1715,7 +1715,7 @@ static int truncate_f(BlockBackend *blk, int argc, char **argv)
* exact=true. It is better to err on the "emit more errors" side
* than to be overly permissive.
*/
ret = blk_truncate(blk, offset, true, PREALLOC_MODE_OFF, 0, &local_err);
ret = blk_truncate(blk, offset, false, PREALLOC_MODE_OFF, 0, &local_err);
if (ret < 0) {
error_report_err(local_err);
return ret;