[Xen-devel] [PATCH] xen_disk: support cache backend option

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Support a backend option "cache" that specifies the cache mode that
should be used to open the disk file or device.

See: http://marc.info/?l=xen-devel&m=137226872905057

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff --git a/hw/xen_disk.c b/hw/xen_disk.c
index f484404..092aa6b 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -94,6 +94,7 @@ struct XenBlkDev {
     char                *type;
     char                *dev;
     char                *devtype;
+    char                *cache;
     const char          *fileproto;
     const char          *filename;
     int                 ring_ref;
@@ -734,6 +735,12 @@ static int blk_init(struct XenDevice *xendev)
     if (blkdev->devtype == NULL) {
         blkdev->devtype = xenstore_read_be_str(&blkdev->xendev, "device-type");
     }
+    if (blkdev->cache == NULL) {
+        blkdev->cache = xenstore_read_be_str(&blkdev->xendev, "cache");
+    }
+    if (blkdev->cache == NULL) {
+        blkdev->cache = g_strdup("writeback");
+    }
 
     /* do we have all we need? */
     if (blkdev->params == NULL ||
@@ -774,6 +781,8 @@ out_error:
     blkdev->dev = NULL;
     g_free(blkdev->devtype);
     blkdev->devtype = NULL;
+    g_free(blkdev->cache);
+    blkdev->cache = NULL;
     return -1;
 }
 
@@ -782,8 +791,14 @@ static int blk_connect(struct XenDevice *xendev)
     struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
     int pers, index, qflags;
 
-    /* read-only ? */
-    qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
+    if (!strcmp(blkdev->cache, "none")) {
+        qflags = BDRV_O_NATIVE_AIO | BDRV_O_NOCACHE;
+    } else if (!strcmp(blkdev->cache, "writethrough")) {
+        qflags = 0;
+    } else {
+        /* default to writeback */
+        qflags = BDRV_O_NATIVE_AIO | BDRV_O_CACHE_WB;
+    }
     if (strcmp(blkdev->mode, "w") == 0) {
         qflags |= BDRV_O_RDWR;
     }
@@ -950,6 +965,7 @@ static int blk_free(struct XenDevice *xendev)
     g_free(blkdev->type);
     g_free(blkdev->dev);
     g_free(blkdev->devtype);
+    g_free(blkdev->cache);
     qemu_bh_delete(blkdev->bh);
     return 0;
 }

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