xen/blkfront: Use QUEUE_ORDERED_DRAIN for old backends
If there's no feature-barrier key in xenstore, then it means its a fairly
old backend which does uncached in-order writes, which means ORDERED_DRAIN
is appropriate.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 6d912ab..ae5f92b 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -420,26 +420,22 @@
static int xlvbd_barrier(struct blkfront_info *info)
{
int err;
- unsigned ordered = QUEUE_ORDERED_NONE;
+ const char *barrier;
- /*
- * If we don't have barrier support, then there's really no
- * way to guarantee write ordering, so we really just have to
- * send writes to the backend and hope for the best. If
- * barriers are supported then we can treat them as proper
- * ordering tags.
- */
- if (info->feature_barrier)
- ordered = QUEUE_ORDERED_TAG;
+ switch (info->feature_barrier) {
+ case QUEUE_ORDERED_DRAIN: barrier = "enabled (drain)"; break;
+ case QUEUE_ORDERED_TAG: barrier = "enabled (tag)"; break;
+ case QUEUE_ORDERED_NONE: barrier = "disabled"; break;
+ default: return -EINVAL;
+ }
- err = blk_queue_ordered(info->rq, ordered);
+ err = blk_queue_ordered(info->rq, info->feature_barrier);
if (err)
return err;
printk(KERN_INFO "blkfront: %s: barriers %s\n",
- info->gd->disk_name,
- info->feature_barrier ? "enabled" : "disabled");
+ info->gd->disk_name, barrier);
return 0;
}
@@ -665,7 +661,7 @@
printk(KERN_WARNING "blkfront: %s: write barrier op failed\n",
info->gd->disk_name);
error = -EOPNOTSUPP;
- info->feature_barrier = 0;
+ info->feature_barrier = QUEUE_ORDERED_NONE;
xlvbd_barrier(info);
}
/* fall through */
@@ -1003,6 +999,7 @@
unsigned long sector_size;
unsigned int binfo;
int err;
+ int barrier;
switch (info->connected) {
case BLKIF_STATE_CONNECTED:
@@ -1043,10 +1040,26 @@
}
err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
- "feature-barrier", "%lu", &info->feature_barrier,
+ "feature-barrier", "%lu", &barrier,
NULL);
+
+ /*
+ * If there's no "feature-barrier" defined, then it means
+ * we're dealing with a very old backend which writes
+ * synchronously; draining will do what needs to get done.
+ *
+ * If there are barriers, then we can do full queued writes
+ * with tagged barriers.
+ *
+ * If barriers are not supported, then there's no much we can
+ * do, so just set ordering to NONE.
+ */
if (err)
- info->feature_barrier = 0;
+ info->feature_barrier = QUEUE_ORDERED_DRAIN;
+ else if (barrier)
+ info->feature_barrier = QUEUE_ORDERED_TAG;
+ else
+ info->feature_barrier = QUEUE_ORDERED_NONE;
err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
if (err) {