Re: [Qemu-devel] [PATCH v2 2/2] xen: dont try setting max grants multiple times

[Anthony PERARD <anthony.perard@citrix.com>]

On Fri, Sep 22, 2017 at 02:07:25PM +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 <jgross@suse.com>

Acked-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks.

> ---
> V2:
> - always call blk_disconnect() from blk_free() in order to have the
>   gnttab device node closed (Anthony Perard)
> ---
>  hw/block/xen_disk.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 62506e3167..e431bd89e8 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;
> +    }
>  }
>  
>  static int blk_free(struct XenDevice *xendev)
> @@ -1334,9 +1345,7 @@ static int blk_free(struct XenDevice *xendev)
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
>      struct ioreq *ioreq;
>  
> -    if (blkdev->blk || blkdev->sring) {
> -        blk_disconnect(xendev);
> -    }
> +    blk_disconnect(xendev);
>  
>      while (!QLIST_EMPTY(&blkdev->freelist)) {
>          ioreq = QLIST_FIRST(&blkdev->freelist);
> @@ -1363,7 +1372,6 @@ 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