Re: [PATCH] block/blkio: do not use open flags in qemu_open()

[Daniel P . Berrangé]

On Tue, Jul 25, 2023 at 01:11:55PM +0200, Stefano Garzarella wrote:
> qemu_open() in blkio_virtio_blk_common_open() is used to open the
> character device (e.g. /dev/vhost-vdpa-0 or /dev/vfio/vfio) or in
> the future eventually the unix socket.
> 
> In all these cases we cannot open the path in read-only mode,
> when the `read-only` option of blockdev is on, because the exchange
> of IOCTL commands for example will fail.
> 
> In order to open the device read-only, we have to use the `read-only`
> property of the libblkio driver as we already do in blkio_file_open().
> 
> Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for 
> virtio-blk")
> Reported-by: Qing Wang <qinwang@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  block/blkio.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index 1798648134..fe9bf8ea5f 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -686,15 +686,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState 
> *bs,
>       * layer through the "/dev/fdset/N" special path.
>       */
>      if (fd_supported) {
> -        int open_flags;
> -
> -        if (flags & BDRV_O_RDWR) {
> -            open_flags = O_RDWR;
> -        } else {
> -            open_flags = O_RDONLY;
> -        }
> -
> -        fd = qemu_open(path, open_flags, errp);

I'd suggest taking the paragraph from the commit message explaining why
it is correct to hardcode O_RDWR and putting it into a comment here.

> +        fd = qemu_open(path, O_RDWR, errp);
>          if (fd < 0) {
>              return -EINVAL;
>          }
> -- 
> 2.41.0
> 
> 

With regards,
Daniel
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