From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752216AbaHTLRK (ORCPT ); Wed, 20 Aug 2014 07:17:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54995 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751714AbaHTLRI (ORCPT ); Wed, 20 Aug 2014 07:17:08 -0400 Date: Wed, 20 Aug 2014 13:17:24 +0200 From: "Michael S. Tsirkin" To: Jiri Pirko Cc: Pankaj Gupta , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net, jasowang@redhat.com, dgibson@redhat.com, vfalico@gmail.com, edumazet@google.com, vyasevic@redhat.com, hkchu@google.com, wuzhy@linux.vnet.ibm.com, xemul@parallels.com, therbert@google.com, bhutchings@solarflare.com, xii@google.com, stephen@networkplumber.org Subject: Re: [RFC 2/4] tuntap: Publish tuntap maximum number of queues as module_param Message-ID: <20140820111724.GE17371@redhat.com> References: <1408369040-1216-1-git-send-email-pagupta@redhat.com> <1408369040-1216-3-git-send-email-pagupta@redhat.com> <20140820105817.GB1916@nanopsycho.orion> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140820105817.GB1916@nanopsycho.orion> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 20, 2014 at 12:58:17PM +0200, Jiri Pirko wrote: > Mon, Aug 18, 2014 at 03:37:18PM CEST, pagupta@redhat.com wrote: > > 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 > >--- > > 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. Additionally, userspace that has the FD should be able to retrieve the value without guessing that the FD is for the tun device (and not e.g. macvtap). To retrieve the value, an ioctl is probably the cleanest approach. To set it, how about a sysctl? I think the limit can also apply to all devices, not just tun. -- MST