Re: [Qemu-devel] [PATCH v2 1/6] qemu-io: Drop write permissions before read-only reopen

[Fam Zheng <famz@redhat.com>]

On Fri, 09/22 14:55, Kevin Wolf wrote:
> qemu-io provides a 'reopen' command that allows switching from writable
> to read-only access. We need to make sure that we don't try to keep
> write permissions to a BlockBackend that becomes read-only, otherwise
> things are going to fail.
> 
> This requires a bdrv_drain() call because otherwise in-flight AIO
> write requests could issue new internal requests while the permission
> has already gone away, which would cause assertion failures. Draining
> the queue doesn't break AIO requests in any new way, bdrv_reopen() would
> drain it anyway only a few lines later.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qemu-io-cmds.c             | 12 ++++++++++++
>  tests/qemu-iotests/187.out |  2 +-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index 2811a89099..3727fb43f3 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c
> @@ -2010,6 +2010,18 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
>          return 0;
>      }
>  
> +    if (!(flags & BDRV_O_RDWR)) {
> +        uint64_t orig_perm, orig_shared_perm;
> +
> +        bdrv_drain(bs);
> +
> +        blk_get_perm(blk, &orig_perm, &orig_shared_perm);
> +        blk_set_perm(blk,
> +                     orig_perm & ~(BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED),
> +                     orig_shared_perm,
> +                     &error_abort);
> +    }
> +
>      qopts = qemu_opts_find(&reopen_opts, NULL);
>      opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
>      qemu_opts_reset(&reopen_opts);
> diff --git a/tests/qemu-iotests/187.out b/tests/qemu-iotests/187.out
> index 68fb944cd5..30b987f71f 100644
> --- a/tests/qemu-iotests/187.out
> +++ b/tests/qemu-iotests/187.out
> @@ -12,7 +12,7 @@ Start from read-write
>  
>  wrote 65536/65536 bytes at offset 0
>  64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> -write failed: Operation not permitted
> +Block node is read-only
>  wrote 65536/65536 bytes at offset 0
>  64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>  *** done
> -- 
> 2.13.5
> 

Reviewed-by: Fam Zheng <famz@redhat.com>