Re: [Qemu-devel] [PATCH] xen: use native disk xenbus protocol if possible

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

On Fri, Jun 17, 2016 at 01:14:56PM +0200, Juergen Gross wrote:
> The qdisk implementation is using the native xenbus protocol only in
> case of no protocol specified at all. As using the explicit 32- or
> 64-bit protocol is slower than the native one due to copying requests
> not by memcpy but element for element, this is not optimal.
> 
> Correct this by using the native protocol in case word sizes of
> frontend and backend match.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  hw/block/xen_disk.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 2862b59..0961fcb 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -976,14 +976,14 @@ static int blk_connect(struct XenDevice *xendev)
>          blkdev->feature_persistent = !!pers;
>      }
>  
> -    blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
> -    if (blkdev->xendev.protocol) {
> -        if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_32) == 0) {
> -            blkdev->protocol = BLKIF_PROTOCOL_X86_32;
> -        }
> -        if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_64) == 0) {
> -            blkdev->protocol = BLKIF_PROTOCOL_X86_64;
> -        }
> +    if (!blkdev->xendev.protocol) {
> +        blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_NATIVE) == 0) {
> +        blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_32) == 0) {
> +        blkdev->protocol = BLKIF_PROTOCOL_X86_32;
> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_64) == 0) {
> +        blkdev->protocol = BLKIF_PROTOCOL_X86_64;

There is one difference with the previous code, in case the protocol is
specified, but it not x86_32 or x86_64, then no blkdev->protocol is
selected (then no ring is initialized). Could you re-add this case?

-- 
Anthony PERARD