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Subject: Re: A small fix for if_em.c, if_igb.c, if_ixgbe.c
From: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
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Date: Mon, 16 Dec 2013 21:06:46 +0100
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To: Adrian Chadd <adrian@freebsd.org>
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Cc: Yong-Hyeon Pyun <pyunyh@gmail.com>, FreeBSD Net <freebsd-net@freebsd.org>,
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On Dec 16, 2013, at 8:36 PM, Adrian Chadd <adrian@freebsd.org> wrote:

> On 13 December 2013 14:17, John Baldwin <jhb@freebsd.org> wrote:
> 
>>> Anyone using if_start() failing as "the frame i just queued failed to
>>> transmit" is broken and well, we should just replace it with
>>> if_transmit().
>> 
>> Hmm,  I was a bit wrong.  Driver if_start routines return void, so they
>> only failed if the IFQ filled up completely.  In that case, I think it is
>> fine to move forward with what you want (only return an error for failures
>> involving the packet passed to if_transmit), but I don't think we should
>> hange if_transmit drivers to just always return 0.
> 
> i agree. if_transmit() should return 0 only if:
> 
> * the driver queued it internally and intends to try transmitting it later;
> * the driver directly dispatched the frame to the hardware.
> 
> If it failed to do either of the above, it should return an error.
> 
> How's that sound?
That sounds good. However, The transport layer is interested in the case
where if_transmit() returns a non-zero value.
Does your statement imply:
if_transmit() returns a non-zero value only if the packet will not
make it on the wire (for example, it failed to queue it).

Best regards
Michael
> 
> 
> -a
>