From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jason Wang <jasowang@redhat.com>
Subject: Re: [RFC 2/4] tuntap: Publish tuntap maximum number of queues as
 module_param
Date: Thu, 21 Aug 2014 12:30:48 +0800
Message-ID: <53F575F8.7000208@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> <20140820111724.GE17371@redhat.com>
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Cc: Pankaj Gupta <pagupta@redhat.com>, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, davem@davemloft.net, 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
To: "Michael S. Tsirkin" <mst@redhat.com>,
	Jiri Pirko <jiri@resnulli.us>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20140820111724.GE17371@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

On 08/20/2014 07:17 PM, Michael S. Tsirkin wrote:
> 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 <pagupta@redhat.com>
>>> > >---
>>> > > 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.