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Subject[PATCH RFC v2 5/5] xen, blkback: negotiate of the number of block rings with the frontend
Date
This commit lets the backend driver advertise the number of available
hardware queues; it also implements gathering from the frontend driver
the number of rings actually available for mapping.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
---
drivers/block/xen-blkback/xenbus.c | 44 +++++++++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index a4f13cc..9ff6ced 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -477,6 +477,34 @@ static void xen_vbd_free(struct xen_vbd *vbd)
vbd->bdev = NULL;
}

+static int xen_advertise_hw_queues(struct xen_blkif *blkif,
+ struct request_queue *q)
+{
+ struct xen_vbd *vbd = &blkif->vbd;
+ struct xenbus_transaction xbt;
+ int err;
+
+ if (q && q->mq_ops)
+ vbd->nr_supported_hw_queues = q->nr_hw_queues;
+
+ err = xenbus_transaction_start(&xbt);
+ if (err) {
+ BUG_ON(!blkif->be);
+ xenbus_dev_fatal(blkif->be->dev, err, "starting transaction (hw queues)");
+ return err;
+ }
+
+ err = xenbus_printf(xbt, blkif->be->dev->nodename, "nr_supported_hw_queues", "%u",
+ blkif->vbd.nr_supported_hw_queues);
+ if (err)
+ xenbus_dev_error(blkif->be->dev, err, "writing %s/nr_supported_hw_queues",
+ blkif->be->dev->nodename);
+
+ xenbus_transaction_end(xbt, 0);
+
+ return err;
+}
+
static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
unsigned major, unsigned minor, int readonly,
int cdrom)
@@ -484,6 +512,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
struct xen_vbd *vbd;
struct block_device *bdev;
struct request_queue *q;
+ int err;

vbd = &blkif->vbd;
vbd->handle = handle;
@@ -522,6 +551,10 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
if (q && blk_queue_secdiscard(q))
vbd->discard_secure = true;

+ err = xen_advertise_hw_queues(blkif, q);
+ if (err)
+ return -ENOENT;
+
DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
handle, blkif->domid);
return 0;
@@ -935,7 +968,16 @@ static int connect_ring(struct backend_info *be)

DPRINTK("%s", dev->otherend);

- blkif->nr_rings = 1;
+ err = xenbus_gather(XBT_NIL, dev->otherend, "nr_blk_rings",
+ "%u", &blkif->nr_rings, NULL);
+ if (err) {
+ /*
+ * Frontend does not support multiqueue; force compatibility
+ * mode of the driver.
+ */
+ blkif->vbd.nr_supported_hw_queues = 0;
+ blkif->nr_rings = 1;
+ }

ring_ref = kzalloc(sizeof(unsigned long) * blkif->nr_rings, GFP_KERNEL);
if (!ring_ref)
--
2.1.0


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