Re: [PATCH 2/4] xen-block: Fix inverted error check in xen_cdrom_realize()

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 17 Jul 2026, Mitsuru Kariya wrote:
> xen_cdrom_realize() checks the return value of blk_attach_dev() with
> 
>     if (!rc) {
>         error_setg_errno(errp, -rc, "failed to create drive");
>         return;
>     }
> 
> but blk_attach_dev() returns 0 on success and a negative errno on
> failure.  The condition is inverted: a successful attach (rc == 0) is
> reported as an error and fails realize, while a real failure (rc < 0)
> is silently ignored.
> 
> Here blk_attach_dev() is called on a BlockBackend just created by
> blk_new(), so blk->dev is NULL and its only failure path (-EBUSY)
> cannot be taken.  Replace the bogus check with an assertion, matching
> the other empty-drive realize paths (scsi-disk, ide, fdc, swim).
> 
> Signed-off-by: Mitsuru Kariya <Mitsuru.Kariya@xxxxxxxxxxxxxxx>


Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
>  hw/block/xen-block.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
> index 474c12fe4a..abf9df2eee 100644
> --- a/hw/block/xen-block.c
> +++ b/hw/block/xen-block.c
> @@ -762,10 +762,7 @@ static void xen_cdrom_realize(XenBlockDevice *blockdev, 
> Error **errp)
>          conf->blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
>  
>          rc = blk_attach_dev(conf->blk, DEVICE(blockdev));
> -        if (!rc) {
> -            error_setg_errno(errp, -rc, "failed to create drive");
> -            return;
> -        }
> +        assert(rc == 0);
>      }
>  
>      blockdev->info = VDISK_READONLY | VDISK_CDROM;
> -- 
> 2.43.0
>