Re: [RFC 2/4] tuntap: Publish tuntap maximum number of queues as module_param

On 08/20/2014 07:17 PM, Michael S. Tsirkin wrote:

On Wed, Aug 20, 2014 at 12:58:17PM +0200, Jiri Pirko wrote:

quoted

quoted

Mon, Aug 18, 2014 at 03:37:18PM CEST, pagupta@redhat.com wrote:

quoted

quoted

This patch publishes maximum number of tun/tap queues allocated as a
read_only module parameter which a user space application like libvirt
can make use of to limit maximum number of queues. Value of read_only
module parameter can be writable only at module load time. If no value is set
at module load time a default value 256 is used which is equal to maximum number
of vCPUS allowed by KVM.

Administrator can specify maximum number of queues only at the driver
module load time.

Signed-off-by: Pankaj Gupta <redacted>
---
drivers/net/tun.c |   13 +++++++++++--
1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index acaaf67..1f518e2 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -119,6 +119,9 @@ struct tap_filter {

#define TUN_FLOW_EXPIRE (3 * HZ)

+static int max_tap_queues = MAX_TAP_QUEUES;
+module_param(max_tap_queues, int, S_IRUGO);

Please do not introduce new module paramaters. Please other ways to
interchange values with userspace.

I suggested this initially, but thinking more about it, I agree.

It's a global limit (necessary to limit memory utilization by
userspace), but it should be possible to change it
after module load.

How about pass this limit through ifr during TUNSETIFF, then
alloc_netdev_mq() can use this limit.