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.rit...@irisa.fr>
>>>
>>> Thanks Pierre, I see why this is needed now
>>>
>>> Acked-by: Mark McLoughlin <mar...@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/
