On Tue, Dec 17, 2013 at 05:08:35PM -0800, Ben Pfaff wrote:
> On Mon, Dec 16, 2013 at 05:57:52PM +0900, Simon Horman wrote:
> > If VLAN acceleration is used when the kernel receives a packet
> > then the outer-most VLAN tag will not be present in the packet
> > when it is received by netdev-linux. Rather, it will be present
> > in auxdata.
> >
> > This patch uses recvmsg() instead of recv() to read auxdata for
> > each packet and if the vlan_tid is set then it is added to the packet.
> >
> > Adding the vlan_tid makes use of headroom available
> > in the buffer parameter of rx_recv.
> >
> > Signed-off-by: Simon Horman <[email protected]>
>
> This patch should be Linux-specific, why does it update netdev-bsd?
>
> I think we should add a comment to netdev_rx_recv() explaining how the
> tailroom in the buffer may get used (you might need 4 bytes more
> tailroom than the actual MTU, and you might get 4 bytes of extra
> headroom in the result).
Sure, how about this?
/* Attempts to receive a packet from 'rx' into 'buffer'.
* If successful, returns 0 and increments the 'size' field of 'buffer'
* by the number of bytes in the received packet, otherwise a positive
* errno value. Returns EAGAIN immediately if no packet is ready to
* be received.
*
* Must return EMSGSIZE, and discard the packet, if the received packet
* is longer than the tailroom of 'buffer'.
*
* Implementations may make use of VLAN_HEADER_LEN bytes of tailroom to
* add a VLAN header which is obtained out-of-band to the packet. If
* this occurs then VLAN_HEADER_LEN bytes of tailroom will no longer be
* available for the packet, otherwise it may be used for the packet
* itself.
*
* It is advised that the tailroom of 'buffer' should be
* VLAN_HEADER_LEN bytes longer than the MTU to allow space for an
* out-of-band VLAN header to be added to the packet.
*
* Specify NULL if this */
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