A small fix for if_em.c, if_igb.c, if_ixgbe.c

[Michael Tuexen]

On Dec 2, 2013, at 3:23 AM, Yonghyeon PYUN <pyunyh at gmail.com> wrote:

> On Fri, Nov 29, 2013 at 06:24:12PM +0100, Michael Tuexen wrote:
>> Dear all,
>> 
>> ifnet(9) says regarding if_transmit():
>> 
>> Transmit a packet on an interface or queue it if the interface is
>> in use.  This function will return ENOBUFS if the devices software
>> and hardware queues are both full.
>> 
>> The drivers for em, igb and ixgbe might also return an error even
>> in the case the packet was enqueued. The attached patches fix this
>> issue.
> 
> How do you know the packet is successfully enqueued but driver
> returns an error?  Do non-buf-ring-aware drivers also show the same
When debugging the issue, I saw the packet on the wire but the if_transmit()
returning ENOBUFS.
> behavior?
I don't know. I saw this issue with the igb driver.
> 
>> 
>> Any comments?
> 
> I'm afraid the patch you posted ignores any errors(i.e.
> m_defrag(9), bus_dma(9) etc) happened during TX processing.
Correct. I want to make sure that if ENOBUFS is returned, the
packet hasn't made it on the wire. The other errors can occur
for the packet provided to if_transmit() or due to packet
processing of other packets. Am I missing something?

Best regards
Michael
> 
>> 
>> Jack: What do you think? Would you prefer to commit the fix if
>> you think it is acceptable?
>> 
>> Best regards
>> Michael
>