Re: [PATCH V4 3/3] tuntap: allow polling/writing/reading when detached

On Tuesday, January 15, 2013 06:48:08 PM Michael S. Tsirkin wrote:

On Tue, Jan 15, 2013 at 06:28:46PM +0800, Jason Wang wrote:

quoted

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 <redacted>
---

 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?

I miss this, something is needed.

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.

Correct, will post another version, thanks.

quoted

@@ -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);

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