[Qemu-devel] [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Qemu-devel] [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Pierre Riteau]

vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
the kernel doesn't support IFF_VNET_HDR.

Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
---
 net/tap-linux.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/net/tap-linux.c b/net/tap-linux.c
index 0f621a2..e4f7e27 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -52,6 +52,8 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
             features & IFF_VNET_HDR) {
             *vnet_hdr = 1;
             ifr.ifr_flags |= IFF_VNET_HDR;
+        } else {
+            *vnet_hdr = 0;
         }
 
         if (vnet_hdr_required && !*vnet_hdr) {
-- 
1.6.5

[Qemu-devel] [PATCH] net: initialize vnet_hdr in net_tap_init()

[Mark McLoughlin]

Hi Pierre,

On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
> the kernel doesn't support IFF_VNET_HDR.

Thanks for the patch, but I'd prefer us to make sure we catch all cases.

Does this work for you?

Thanks,
Mark.

From: Mark McLoughlin <markmc@redhat.com>
Subject: [PATCH] net: initialize vnet_hdr in net_tap_init()

Don't assume that all tap_open() implementations will set it to
zero if VNET_HDR support isn't found.

Fixes tap networking on host kernels lacking IFF_VNET_HDR support.

Reported-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
---
 net/tap.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index d34feec..7fb9e16 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -378,7 +378,7 @@ static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
 int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan)
 {
     TAPState *s;
-    int fd, vnet_hdr;
+    int fd, vnet_hdr = 0;
 
     if (qemu_opt_get(opts, "fd")) {
         if (qemu_opt_get(opts, "ifname") ||
-- 
1.6.5.2

Re: [Qemu-devel] [PATCH] net: initialize vnet_hdr in net_tap_init()

[Pierre Riteau]

On 24 nov. 2009, at 11:05, Mark McLoughlin wrote:

> Hi Pierre,
> 
> On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
>> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
>> the kernel doesn't support IFF_VNET_HDR.
> 
> Thanks for the patch, but I'd prefer us to make sure we catch all cases.
> 
> Does this work for you?
> 
> Thanks,
> Mark.

No it doesn't fix the problem, since vnet_hdr is then changed to 1 in net_tap_init by this line, just before calling tap_open:

    *vnet_hdr = qemu_opt_get_bool(opts, "vnet_hdr", 1);

I run qemu like this: sudo qemu -m 1024 -hda /mnt/hda.img -net nic,macaddr=DE:AD:BE:EF:69:25 -net tap,script=/home/priteau/qemu-ifup -boot c -vnc 0:0

-- 
Pierre Riteau -- http://perso.univ-rennes1.fr/pierre.riteau/

[Qemu-devel] Re: [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Mark McLoughlin]

On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
> the kernel doesn't support IFF_VNET_HDR.
> 
> Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>

Thanks Pierre, I see why this is needed now

Acked-by: Mark McLoughlin <markmc@redhat.com>

Cheers,
Mark.

Re: [Qemu-devel] Re: [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Pierre Riteau]

On 24 nov. 2009, at 11:28, Mark McLoughlin wrote:

> On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
>> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
>> the kernel doesn't support IFF_VNET_HDR.
>> 
>> Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
> 
> Thanks Pierre, I see why this is needed now
> 
> Acked-by: Mark McLoughlin <markmc@redhat.com>
> 
> Cheers,
> Mark.


Thanks for your rapid answer!

BTW, every time I run qemu I see this error message:

    TUNSETOFFLOAD ioctl() failed: Invalid argument

It is caused by the piece of code at the end of net/tap-linux.c:

    if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
        offload &= ~TUN_F_UFO;
        if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
            fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
                    strerror(errno));
        }
    }

Isn't there a way to detect whether the kernel supports the TUNSETOFFLOAD ioctl at all?

-- 
Pierre Riteau -- http://perso.univ-rennes1.fr/pierre.riteau/

Re: [Qemu-devel] Re: [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Mark McLoughlin]

On Tue, 2009-11-24 at 12:17 +0100, Pierre Riteau wrote:
> On 24 nov. 2009, at 11:28, Mark McLoughlin wrote:
> 
> > On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
> >> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
> >> the kernel doesn't support IFF_VNET_HDR.
> >> 
> >> Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
> > 
> > Thanks Pierre, I see why this is needed now
> > 
> > Acked-by: Mark McLoughlin <markmc@redhat.com>
> > 
> > Cheers,
> > Mark.
> 
> 
> Thanks for your rapid answer!
> 
> BTW, every time I run qemu I see this error message:
> 
>     TUNSETOFFLOAD ioctl() failed: Invalid argument
> 
> It is caused by the piece of code at the end of net/tap-linux.c:
> 
>     if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
>         offload &= ~TUN_F_UFO;
>         if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
>             fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
>                     strerror(errno));
>         }
>     }
> 
> Isn't there a way to detect whether the kernel supports the
> TUNSETOFFLOAD ioctl at all?

The kernel will set errno to EINVAL if TUNSETOFFLOAD isn't supported, so
we could just ignore that case:

     if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
          offload &= ~TUN_F_UFO;
          if (ioctl(fd, TUNSETOFFLOAD, offload) != 0 && errno != EINVAL) {
              fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
                      strerror(errno));
          }
      }

The only concern is that we'll also miss out on an error message if
EINVAL is set for another reason. Currently, the only other reason if we
pass a offload flag not supported by the kernel, but that should never
happen.

Feel free to send a patch with that change and I'll ack it

Thanks,
Mark.

Re: [Qemu-devel] Re: [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Pierre Riteau]

On 24 nov. 2009, at 12:22, Mark McLoughlin wrote:

> On Tue, 2009-11-24 at 12:17 +0100, Pierre Riteau wrote:
>> On 24 nov. 2009, at 11:28, Mark McLoughlin wrote:
>> 
>>> On Tue, 2009-11-24 at 10:06 +0100, Pierre Riteau wrote:
>>>> vnet_hdr is initialized at 1 by default. We need to reset it to 0 if
>>>> the kernel doesn't support IFF_VNET_HDR.
>>>> 
>>>> Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
>>> 
>>> Thanks Pierre, I see why this is needed now
>>> 
>>> Acked-by: Mark McLoughlin <markmc@redhat.com>
>>> 
>>> Cheers,
>>> Mark.
>> 
>> 
>> Thanks for your rapid answer!
>> 
>> BTW, every time I run qemu I see this error message:
>> 
>>    TUNSETOFFLOAD ioctl() failed: Invalid argument
>> 
>> It is caused by the piece of code at the end of net/tap-linux.c:
>> 
>>    if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
>>        offload &= ~TUN_F_UFO;
>>        if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
>>            fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
>>                    strerror(errno));
>>        }
>>    }
>> 
>> Isn't there a way to detect whether the kernel supports the
>> TUNSETOFFLOAD ioctl at all?
> 
> The kernel will set errno to EINVAL if TUNSETOFFLOAD isn't supported, so
> we could just ignore that case:
> 
>     if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
>          offload &= ~TUN_F_UFO;
>          if (ioctl(fd, TUNSETOFFLOAD, offload) != 0 && errno != EINVAL) {
>              fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
>                      strerror(errno));
>          }
>      }
> 
> The only concern is that we'll also miss out on an error message if
> EINVAL is set for another reason. Currently, the only other reason if we
> pass a offload flag not supported by the kernel, but that should never
> happen.
> 
> Feel free to send a patch with that change and I'll ack it
> 
> Thanks,
> Mark.
> 


Couldn't we probe the kernel with a 0 offload value to check if it supports TUNSETOFFLOAD?
I tried the following and it works on my 2.6.26 Debian kernel.
What do you think? I will send a proper patch if you agree.

diff --git a/net/tap-linux.c b/net/tap-linux.c
index 0f621a2..e038e1a 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -129,6 +129,11 @@ void tap_fd_set_offload(int fd, int csum, int tso4,
 {
     unsigned int offload = 0;
 
+    /* Check if our kernel supports TUNSETOFFLOAD */
+    if (ioctl(fd, TUNSETOFFLOAD, 0) != 0 && errno == EINVAL) {
+        return;
+    }
+
     if (csum) {
         offload |= TUN_F_CSUM;
         if (tso4)

-- 
Pierre Riteau -- http://perso.univ-rennes1.fr/pierre.riteau/

Re: [Qemu-devel] Re: [PATCH] Fix TAP networking on host kernels without IFF_VNET_HDR support

[Mark McLoughlin]

On Tue, 2009-11-24 at 22:27 +0100, Pierre Riteau wrote:
> On 24 nov. 2009, at 12:22, Mark McLoughlin wrote:
> 
> > On Tue, 2009-11-24 at 12:17 +0100, Pierre Riteau wrote:

> >> Isn't there a way to detect whether the kernel supports the
> >> TUNSETOFFLOAD ioctl at all?
> > 
> > The kernel will set errno to EINVAL if TUNSETOFFLOAD isn't supported, so
> > we could just ignore that case:
> > 
> >     if (ioctl(fd, TUNSETOFFLOAD, offload) != 0) {
> >          offload &= ~TUN_F_UFO;
> >          if (ioctl(fd, TUNSETOFFLOAD, offload) != 0 && errno != EINVAL) {
> >              fprintf(stderr, "TUNSETOFFLOAD ioctl() failed: %s\n",
> >                      strerror(errno));
> >          }
> >      }
> > 
> > The only concern is that we'll also miss out on an error message if
> > EINVAL is set for another reason. Currently, the only other reason if we
> > pass a offload flag not supported by the kernel, but that should never
> > happen.
> > 
> > Feel free to send a patch with that change and I'll ack it
....
> 
> Couldn't we probe the kernel with a 0 offload value to check if it supports TUNSETOFFLOAD?
> I tried the following and it works on my 2.6.26 Debian kernel.
> What do you think? I will send a proper patch if you agree.
> 
> diff --git a/net/tap-linux.c b/net/tap-linux.c
> index 0f621a2..e038e1a 100644
> --- a/net/tap-linux.c
> +++ b/net/tap-linux.c
> @@ -129,6 +129,11 @@ void tap_fd_set_offload(int fd, int csum, int tso4,
>  {
>      unsigned int offload = 0;
>  
> +    /* Check if our kernel supports TUNSETOFFLOAD */
> +    if (ioctl(fd, TUNSETOFFLOAD, 0) != 0 && errno == EINVAL) {
> +        return;
> +    }
> +

It's not ideal because a) it's another syscall and b) you're briefly
disabling any flags that may have been set previously ... but in our
case, neither is a real concern and it's a nice, simple solution.

So, sounds good to me :)

Cheers,
Mark.