Re: [Qemu-devel] [PATCH 2/2] xen: dont try setting max grants multiple times

[Anthony PERARD]

On Tue, Sep 19, 2017 at 01:50:55PM +0200, Juergen Gross wrote:
> Trying to call xengnttab_set_max_grants() with the same file handle
> might fail on some kernels, as this operation is allowed only once.
> 
> This is a problem for the qdisk backend as blk_connect() can be
> called multiple times for a domain, e.g. in case grub-xen is being
> used to boot it.
> 
> So instead of letting the generic backend code open the gnttab device
> do it in blk_connect() and close it again in blk_disconnect.
> 
> Signed-off-by: Juergen Gross <address@hidden>
> ---
>  hw/block/xen_disk.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 6632746250..7cff8863cb 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -1220,6 +1220,12 @@ static int blk_connect(struct XenDevice *xendev)
>      /* Add on the number needed for the ring pages */
>      max_grants += blkdev->nr_ring_ref;
>  
> +    blkdev->xendev.gnttabdev = xengnttab_open(NULL, 0);
> +    if (blkdev->xendev.gnttabdev == NULL) {
> +        xen_pv_printf(xendev, 0, "xengnttab_open failed: %s\n",
> +                      strerror(errno));
> +        return -1;
> +    }
>      if (xengnttab_set_max_grants(blkdev->xendev.gnttabdev, max_grants)) {
>          xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
>                        strerror(errno));
> @@ -1327,6 +1333,11 @@ static void blk_disconnect(struct XenDevice *xendev)
>          }
>          blkdev->feature_persistent = false;
>      }
> +
> +    if (blkdev->xendev.gnttabdev) {
> +        xengnttab_close(blkdev->xendev.gnttabdev);
> +        blkdev->xendev.gnttabdev = NULL;
> +    }

I think blk_disconnect needs to be called from blk_free in case where
the gnttabdev is not closed (like it is done when blk or the sring are
not cleared, in blk_free).

>  }

>  static int blk_free(struct XenDevice *xendev)
> @@ -1363,7 +1374,6 @@ static void blk_event(struct XenDevice *xendev)
>  
>  struct XenDevOps xen_blkdev_ops = {
>      .size       = sizeof(struct XenBlkDev),
> -    .flags      = DEVOPS_FLAG_NEED_GNTDEV,
>      .alloc      = blk_alloc,
>      .init       = blk_init,
>      .initialise    = blk_connect,
> -- 
> 2.12.3
> 

-- 
Anthony PERARD