[Qemu-devel] [PATCH v2] xen: use native disk xenbus protocol if possible

[Juergen Gross]

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 <address@hidden>
---
V2: use native protocol in case of unknown protocol specified as
    requested by Anthony Perard
---
 hw/block/xen_disk.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 90aca73..d0aae67 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -975,14 +975,16 @@ 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;
+    } else {
+        blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
     }
 
     blkdev->sring = xengnttab_map_grant_ref(blkdev->xendev.gnttabdev,
-- 
2.6.6