From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH V4 3/3] tuntap: allow polling/writing/reading when detached Date: Tue, 15 Jan 2013 18:48:08 +0200 Message-ID: <20130115164808.GA8792@redhat.com> References: <1358245726-16250-1-git-send-email-jasowang@redhat.com> <1358245726-16250-4-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <1358245726-16250-4-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Jan 15, 2013 at 06:28:46PM +0800, Jason Wang wrote: > We forbid polling, writing and reading when the file were detached, this may > complex the user in several cases: > > - when guest pass some buffers to vhost/qemu and then disable some queues, > vhost/qemu needs to to its own cleanup which is complex. We can do this simply > by allowing a user can still write to an disabled queue to handle this. And > user can still do read but just nothing returned. > - align the polling behavior with macvtap which never fails when the queue is > created. this can simplify the polling errors handling of its user (e.g vhost) > > Signed-off-by: Jason Wang > --- > drivers/net/tun.c | 18 +++++++++++------- > 1 files changed, 11 insertions(+), 7 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index af372d0..eb68937 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -307,7 +307,7 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash, > > rcu_read_lock(); > > - if (tun->numqueues == 1) > + if (tun->numqueues == 1 || queue_index >= tun->numqueues) > goto unlock; > > e = tun_flow_find(head, rxhash); Hmm I don't understand - does something ensure that queue_index is > numqueues if the queue is disabled? Can we check tun->disabled and skip tun_flow_update completely? We might need to switch to rcu_assign for tun->disabled for this but otherwise it looks easy. > @@ -406,21 +406,21 @@ static void __tun_detach(struct tun_file *tfile, bool clean) > > tun = rtnl_dereference(tfile->tun); > > - if (tun) { > + if (tun && !tfile->detached) { > u16 index = tfile->queue_index; > BUG_ON(index >= tun->numqueues); > dev = tun->dev; > > rcu_assign_pointer(tun->tfiles[index], > tun->tfiles[tun->numqueues - 1]); > - rcu_assign_pointer(tfile->tun, NULL); > ntfile = rtnl_dereference(tun->tfiles[index]); > ntfile->queue_index = index; > > --tun->numqueues; > - if (clean) > + if (clean) { > + rcu_assign_pointer(tfile->tun, NULL); > sock_put(&tfile->sk); > - else > + } else > tun_disable_queue(tun, tfile); > > synchronize_net(); > @@ -465,6 +465,10 @@ static void tun_detach_all(struct net_device *dev) > rcu_assign_pointer(tfile->tun, NULL); > --tun->numqueues; > } > + list_for_each_entry(tfile, &tun->disabled, next) { > + wake_up_all(&tfile->wq.wait); > + rcu_assign_pointer(tfile->tun, NULL); > + } > BUG_ON(tun->numqueues != 0); > > synchronize_net(); > @@ -491,7 +495,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file) > int err; > > err = -EINVAL; > - if (rtnl_dereference(tfile->tun)) > + if (rtnl_dereference(tfile->tun) && !tfile->detached) > goto out; > > err = -EBUSY; > @@ -1795,7 +1799,7 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr) > ret = tun_attach(tun, file); > } else if (ifr->ifr_flags & IFF_DETACH_QUEUE) { > tun = rtnl_dereference(tfile->tun); > - if (!tun || !(tun->flags & TUN_TAP_MQ)) > + if (!tun || !(tun->flags & TUN_TAP_MQ) || tfile->detached) > ret = -EINVAL; > else > __tun_detach(tfile, false); > -- > 1.7.1