Subject: Re: [PATCH v2] macvtap: Correctly set tap features when IFF_VNET_HDR is disabled.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 14 Aug 2013 22:23:06 +0300

On Wed, Aug 14, 2013 at 03:14:33PM -0400, Vlad Yasevich wrote:
> On 08/14/2013 01:50 PM, Michael S. Tsirkin wrote:
> >On Wed, Aug 14, 2013 at 01:03:40PM -0400, Vlad Yasevich wrote:
> >>When the user turns off IFF_VNET_HDR flag, attempts to change
> >>offload features via TUNSETOFFLOAD do not work.  This could cause
> >>GSO packets to be delivered to the user when the user is
> >>not prepared to handle them.
> >>
> >>To solve, allow processing of TUNSETOFFLOAD when IFF_VNET_HDR is
> >>disabled.  Treat any attempt to enable offloads as an error in
> >>this case.
> >>We also need to update the TUN_FEATURES mask to include all checksum
> >>options as the underlying device may have something other then
> >>HW_CSUM set.
> >
> >This last looks like a completely unrelated change,
> >does it not?
> >Would be nice to have it in a separate patchset with some
> >examples of broken configurations.
> 
> sure.  can do.
> 
> >
> >>
> >>Change since v1:
> >>   - Removed the call to update offloads when IFF_VNET_HDR is turned off.
> >>   - Changed the macvtap version of TUN_OFFLOADS to include all checksum
> >>     offloads since the physical nic may have them set.
> >>   - Treat enabling of offloads without vnet_hdr support as error.
> >>
> >>Signed-off-by: Vlad Yasevich <[email-masked]>
> >>---
> >>  drivers/net/macvtap.c | 12 +++++++-----
> >>  1 file changed, 7 insertions(+), 5 deletions(-)
> >>
> >>diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> >>index a98fb0e..3acfc37 100644
> >>--- a/drivers/net/macvtap.c
> >>+++ b/drivers/net/macvtap.c
> >>@@ -65,7 +65,7 @@ static struct cdev macvtap_cdev;
> >>
> >>  static const struct proto_ops macvtap_socket_ops;
> >>
> >>-#define TUN_OFFLOADS (NETIF_F_HW_CSUM | NETIF_F_TSO_ECN | NETIF_F_TSO | \
> >>+#define TUN_OFFLOADS (NETIF_F_ALL_CSUM | NETIF_F_TSO_ECN | NETIF_F_TSO | \
> >>  		      NETIF_F_TSO6 | NETIF_F_UFO)
> >>  #define RX_OFFLOADS (NETIF_F_GRO | NETIF_F_LRO)
> >>  /*
> >>@@ -1024,6 +1024,12 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
> >>  	if (!vlan)
> >>  		return -ENOLINK;
> >>
> >>+	/* If the user is trying to set offloads while IFF_VNET_HDR is
> >>+	 * off, report it as an error.
> >>+	 */
> >>+	if (!(q->flags & IFF_VNET_HDR) && arg)
> >>+		return -EINVAL;
> >>+
> >
> >This function has a single caller so it should matter,
> >but I'm just curious why are you moving the test here from
> >macvtap_ioctl?
> >
> 
> I thought the same thing.  I can certainly move it back.  Will make
> the patch smaller.
> 
> >>  	features = vlan->dev->features;
> >>
> >>  	if (arg & TUN_F_CSUM) {
> >>@@ -1155,10 +1161,6 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> >>  			    TUN_F_TSO_ECN | TUN_F_UFO))
> >>  			return -EINVAL;
> >>
> >>-		/* TODO: only accept frames with the features that
> >>-			 got enabled for forwarded frames */
> >
> >Why do you drop this btw? you disagree we should do this
> >eventually? Maybe a separate patch too.
> 
> I thought that this comment related to the check for VNET_HDR.
> I am having a hard time understanding the meaning behind this comment.
> Is the meaning that if GSO is disabled, we shouldn't accept GSO?  This
> kind the reverse of what we've been doing.

I see, you mean 3e4f8b787370978733ca6cae452720a4f0c296b8
actually addressed this comment?
I think you are right, and we can drop it, though maybe cleaner
to do it by a separate patch.

> Or is more along the lines of dropping dropping GSO_GRE for now since
> we don't support that offload function yet?
> 
> -vlad

Confused. What don't we support?

> >
> >>-		if (!(q->flags & IFF_VNET_HDR))
> >>-			return  -EINVAL;
> >>  		rtnl_lock();
> >>  		ret = set_offload(q, arg);
> >>  		rtnl_unlock();
> >>--
> >>1.8.1.4