xen-blkfront: Introduce BLKIF_OP_FLUSH_DISKCACHE support.
If the backend supports the 'feature-flush-cache' mode, use that
instead of the 'feature-barrier' support.
Currently there are three backends that support the 'feature-flush-cache'
mode: NetBSD, Solaris and Linux kernel. The 'flush' option is much
light-weight version than the 'barrier' support so lets try to use as
there are no filesystems in the kernel that use full barriers anymore.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2075981..b536a9c 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -97,6 +97,7 @@
struct blk_shadow shadow[BLK_RING_SIZE];
unsigned long shadow_free;
unsigned int feature_flush;
+ unsigned int flush_op;
int is_ready;
};
@@ -250,8 +251,7 @@
/*
* Generate a Xen blkfront IO request from a blk layer request. Reads
- * and writes are handled as expected. Since we lack a loose flush
- * request, we map flushes into a full ordered barrier.
+ * and writes are handled as expected.
*
* @req: a request struct
*/
@@ -293,14 +293,13 @@
if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
/*
- * Ideally we could just do an unordered
- * flush-to-disk, but all we have is a full write
- * barrier at the moment. However, a barrier write is
+ * Ideally we can do an unordered flush-to-disk. In case the
+ * backend onlysupports barriers, use that. A barrier request
* a superset of FUA, so we can implement it the same
* way. (It's also a FLUSH+FUA, since it is
* guaranteed ordered WRT previous writes.)
*/
- ring_req->operation = BLKIF_OP_WRITE_BARRIER;
+ ring_req->operation = info->flush_op;
}
ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
@@ -433,8 +432,11 @@
static void xlvbd_flush(struct blkfront_info *info)
{
blk_queue_flush(info->rq, info->feature_flush);
- printk(KERN_INFO "blkfront: %s: barriers %s\n",
+ printk(KERN_INFO "blkfront: %s: %s: %s\n",
info->gd->disk_name,
+ info->flush_op == BLKIF_OP_WRITE_BARRIER ?
+ "barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
+ "flush diskcache" : "barrier or flush"),
info->feature_flush ? "enabled" : "disabled");
}
@@ -720,15 +722,20 @@
error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
switch (bret->operation) {
+ case BLKIF_OP_FLUSH_DISKCACHE:
case BLKIF_OP_WRITE_BARRIER:
if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
- printk(KERN_WARNING "blkfront: %s: write barrier op failed\n",
+ printk(KERN_WARNING "blkfront: %s: write %s op failed\n",
+ info->flush_op == BLKIF_OP_WRITE_BARRIER ?
+ "barrier" : "flush disk cache",
info->gd->disk_name);
error = -EOPNOTSUPP;
}
if (unlikely(bret->status == BLKIF_RSP_ERROR &&
info->shadow[id].req.nr_segments == 0)) {
- printk(KERN_WARNING "blkfront: %s: empty write barrier op failed\n",
+ printk(KERN_WARNING "blkfront: %s: empty write %s op failed\n",
+ info->flush_op == BLKIF_OP_WRITE_BARRIER ?
+ "barrier" : "flush disk cache",
info->gd->disk_name);
error = -EOPNOTSUPP;
}
@@ -736,6 +743,7 @@
if (error == -EOPNOTSUPP)
error = 0;
info->feature_flush = 0;
+ info->flush_op = 0;
xlvbd_flush(info);
}
/* fall through */
@@ -1100,7 +1108,7 @@
unsigned long sector_size;
unsigned int binfo;
int err;
- int barrier;
+ int barrier, flush;
switch (info->connected) {
case BLKIF_STATE_CONNECTED:
@@ -1140,6 +1148,9 @@
return;
}
+ info->feature_flush = 0;
+ info->flush_op = 0;
+
err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
"feature-barrier", "%d", &barrier,
NULL);
@@ -1151,11 +1162,23 @@
*
* If there are barriers, then we use flush.
*/
- info->feature_flush = 0;
-
- if (!err && barrier)
+ if (!err && barrier) {
info->feature_flush = REQ_FLUSH | REQ_FUA;
+ info->flush_op = BLKIF_OP_WRITE_BARRIER;
+ }
+ /*
+ * And if there is "feature-flush-cache" use that above
+ * barriers.
+ */
+ err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+ "feature-flush-cache", "%d", &flush,
+ NULL);
+ if (!err && flush) {
+ info->feature_flush = REQ_FLUSH;
+ info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
+ }
+
err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
if (err) {
xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",