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raw-format: drop WRITE and RESIZE child perms when possible

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The following command-line fails due to a permissions conflict:

  $ qemu-storage-daemon \
      --blockdev driver=nvme,node-name=nvme0,device=0000:08:00.0,namespace=1 \
      --blockdev driver=raw,node-name=l1-1,file=nvme0,offset=0,size=1073741824 \
      --blockdev driver=raw,node-name=l1-2,file=nvme0,offset=1073741824,size=1073741824 \
      --nbd-server addr.type=unix,addr.path=/tmp/nbd.sock,max-connections=2 \
      --export type=nbd,id=nbd-l1-1,node-name=l1-1,name=l1-1,writable=on \
      --export type=nbd,id=nbd-l1-2,node-name=l1-2,name=l1-2,writable=on

  qemu-storage-daemon: --export type=nbd,id=nbd-l1-1,node-name=l1-1,name=l1-1,writable=on: Permission conflict on node 'nvme0': permissions 'resize' are both required by node 'l1-1' (uses node 'nvme0' as 'file' child) and unshared by node 'l1-2' (uses node 'nvme0' as 'file' child).

The problem is that block/raw-format.c relies on bdrv_default_perms() to
set permissions on the nvme node. The default permissions add RESIZE in
anticipation of a format driver like qcow2 that needs to grow the image
file. This fails because RESIZE is unshared, so we cannot get the RESIZE
permission.

Max Reitz pointed out that block/crypto.c already handles this case by
implementing a custom ->bdrv_child_perm() function that adjusts the
result of bdrv_default_perms().

This patch takes the same approach in block/raw-format.c so that RESIZE
is only required if it's actually necessary (e.g. the parent is qcow2).

Cc: Max Reitz <mreitz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210726122839.822900-1-stefanha@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-07-26 13:28:39 +01:00 committed by Hanna Reitz
parent 8cca0bd289
commit b68ce82409
1 changed files with 20 additions and 1 deletions
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21
block/raw-format.c
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@ -580,6 +580,25 @@ static void raw_cancel_in_flight(BlockDriverState *bs)
bdrv_cancel_in_flight(bs->file->bs);
}
static void raw_child_perm(BlockDriverState *bs, BdrvChild *c,
BdrvChildRole role,
BlockReopenQueue *reopen_queue,
uint64_t parent_perm, uint64_t parent_shared,
uint64_t *nperm, uint64_t *nshared)
{
bdrv_default_perms(bs, c, role, reopen_queue, parent_perm,
parent_shared, nperm, nshared);
/*
* bdrv_default_perms() may add WRITE and/or RESIZE (see comment in
* bdrv_default_perms_for_storage() for an explanation) but we only need
* them if they are in parent_perm. Drop WRITE and RESIZE whenever possible
* to avoid permission conflicts.
*/
*nperm &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
*nperm |= parent_perm & (BLK_PERM_WRITE | BLK_PERM_RESIZE);
}
BlockDriver bdrv_raw = {
.format_name = "raw",
.instance_size = sizeof(BDRVRawState),
@ -588,7 +607,7 @@ BlockDriver bdrv_raw = {
.bdrv_reopen_commit = &raw_reopen_commit,
.bdrv_reopen_abort = &raw_reopen_abort,
.bdrv_open = &raw_open,
.bdrv_child_perm = bdrv_default_perms,
.bdrv_child_perm = raw_child_perm,
.bdrv_co_create_opts = &raw_co_create_opts,
.bdrv_co_preadv = &raw_co_preadv,
.bdrv_co_pwritev = &raw_co_pwritev,