Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

Sometimes a user would like to control the amount of IO queues to be
created for a block device. For example, for limiting the memory
footprint of virtio-blk devices.

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---

changes from v1:
 - use param_set_uint_minmax (from Christoph)
 - added "Should > 0" to module description

Note: This commit apply on top of Jens's branch for-5.15/drivers
---
 drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4b49df2dfd23..9332fc4e9b31 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c

@@ -24,6 +24,22 @@
 /* The maximum number of sg elements that fit into a virtqueue */
 #define VIRTIO_BLK_MAX_SG_ELEMS 32768
 
+static int virtblk_queue_count_set(const char *val,
+		const struct kernel_param *kp)
+{
+	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
+}
+
+static const struct kernel_param_ops queue_count_ops = {
+	.set = virtblk_queue_count_set,
+	.get = param_get_uint,
+};
+
+static unsigned int num_io_queues;
+module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
+MODULE_PARM_DESC(num_io_queues,
+		 "Number of IO virt queues to use for blk device. Should > 0");
+
 static int major;
 static DEFINE_IDA(vd_index_ida);
 

@@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
 	if (err)
 		num_vqs = 1;
 
-	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
+	num_vqs = min_t(unsigned int,
+			min_not_zero(num_io_queues, nr_cpu_ids),
+			num_vqs);