Re: [Xen-devel] [PATCH v2 1/3] xen-disk: only advertize feature-persistent if grant copy is not available

[Stefano Stabellini]

On Wed, 21 Jun 2017, Paul Durrant wrote:
> If grant copy is available then it will always be used in preference to
> persistent maps. In this case feature-persistent should not be advertized
> to the frontend, otherwise it may needlessly copy data into persistently
> granted buffers.
> 
> Signed-off-by: Paul Durrant 

Reviewed-by: Stefano Stabellini 


> ---
> Cc: Stefano Stabellini 
> Cc: Anthony Perard 
> Cc: Kevin Wolf 
> Cc: Max Reitz 
> ---
>  hw/block/xen_disk.c | 15 ---
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 3a22805fbc..9b06e3aa81 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -1023,11 +1023,18 @@ static int blk_init(struct XenDevice *xendev)
>  
>  blkdev->file_blk  = BLOCK_SIZE;
>  
> +blkdev->feature_grant_copy =
> +(xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 
> 0);
> +
> +xen_pv_printf(>xendev, 3, "grant copy operation %s\n",
> +  blkdev->feature_grant_copy ? "enabled" : "disabled");
> +
>  /* fill info
>   * blk_connect supplies sector-size and sectors
>   */
>  xenstore_write_be_int(>xendev, "feature-flush-cache", 1);
> -xenstore_write_be_int(>xendev, "feature-persistent", 1);
> +xenstore_write_be_int(>xendev, "feature-persistent",
> +  !blkdev->feature_grant_copy);
>  xenstore_write_be_int(>xendev, "info", info);
>  
>  blk_parse_discard(blkdev);
> @@ -1202,12 +1209,6 @@ static int blk_connect(struct XenDevice *xendev)
>  
>  xen_be_bind_evtchn(>xendev);
>  
> -blkdev->feature_grant_copy =
> -(xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 
> 0);
> -
> -xen_pv_printf(>xendev, 3, "grant copy operation %s\n",
> -  blkdev->feature_grant_copy ? "enabled" : "disabled");
> -
>  xen_pv_printf(>xendev, 1, "ok: proto %s, ring-ref %d, "
>"remote port %d, local port %d\n",
>blkdev->xendev.protocol, blkdev->ring_ref,
> -- 
> 2.11.0
> 

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[Xen-devel] [PATCH v2 1/3] xen-disk: only advertize feature-persistent if grant copy is not available

[Paul Durrant]

If grant copy is available then it will always be used in preference to
persistent maps. In this case feature-persistent should not be advertized
to the frontend, otherwise it may needlessly copy data into persistently
granted buffers.

Signed-off-by: Paul Durrant 
---
Cc: Stefano Stabellini 
Cc: Anthony Perard 
Cc: Kevin Wolf 
Cc: Max Reitz 
---
 hw/block/xen_disk.c | 15 ---
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 3a22805fbc..9b06e3aa81 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -1023,11 +1023,18 @@ static int blk_init(struct XenDevice *xendev)
 
 blkdev->file_blk  = BLOCK_SIZE;
 
+blkdev->feature_grant_copy =
+(xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);
+
+xen_pv_printf(>xendev, 3, "grant copy operation %s\n",
+  blkdev->feature_grant_copy ? "enabled" : "disabled");
+
 /* fill info
  * blk_connect supplies sector-size and sectors
  */
 xenstore_write_be_int(>xendev, "feature-flush-cache", 1);
-xenstore_write_be_int(>xendev, "feature-persistent", 1);
+xenstore_write_be_int(>xendev, "feature-persistent",
+  !blkdev->feature_grant_copy);
 xenstore_write_be_int(>xendev, "info", info);
 
 blk_parse_discard(blkdev);
@@ -1202,12 +1209,6 @@ static int blk_connect(struct XenDevice *xendev)
 
 xen_be_bind_evtchn(>xendev);
 
-blkdev->feature_grant_copy =
-(xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);
-
-xen_pv_printf(>xendev, 3, "grant copy operation %s\n",
-  blkdev->feature_grant_copy ? "enabled" : "disabled");
-
 xen_pv_printf(>xendev, 1, "ok: proto %s, ring-ref %d, "
   "remote port %d, local port %d\n",
   blkdev->xendev.protocol, blkdev->ring_ref,
-- 
2.11.0


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