Override default cache mode for disk images to write-back

Upstream qemu changed the default cache mode to write-through (ie,
O_DSYNC) which is much slower.  We do not need this as we have
explicit control of cacheing with the IDE cache control commands.

Original patch by Yang Zhang modified by Ian Jackson.

Signed-off-by: Yang Zhang <yang.zhang@intel.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/xenstore.c b/xenstore.c
index 6bfcdbbbe42e4c0930e4bc58cb4d4679ce21efcd..928e950c070c6e03c0aa5923075acf26898fd5ce 100644 (file)
--- a/xenstore.c
+++ b/xenstore.c
@@ -472,7 +472,7 @@ void xenstore_parse_domain_config(int hvm_domid)
 #ifdef CONFIG_STUBDOM
         if (pasprintf(&danger_buf, "%s/device/vbd/%s", danger_path, e_danger[i]) == -1)
             continue;
-       if (bdrv_open2(bs, danger_buf, 0 /* snapshot */, &bdrv_vbd) == 0) {
+       if (bdrv_open2(bs, danger_buf, BDRV_O_CACHE_WB /* snapshot and write-back */, &bdrv_vbd) == 0) {
            pstrcpy(bs->filename, sizeof(bs->filename), params);
        } else
 #endif
@@ -498,7 +498,7 @@ void xenstore_parse_domain_config(int hvm_domid)
                }
            }
             pstrcpy(bs->filename, sizeof(bs->filename), params);
-            if (bdrv_open2(bs, params, 0 /* snapshot */, format) < 0)
+            if (bdrv_open2(bs, params, BDRV_O_CACHE_WB /* snapshot and write-back */, format) < 0)
                 fprintf(stderr, "qemu: could not open vbd '%s' or hard disk image '%s' (drv '%s' format '%s')\n", buf, params, drv ? drv : "?", format ? format->format_name : "0");
         }