netdev - Re: skb_try_coalesce bug?

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Message-ID: <1398197116.29946.60.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 22 Apr 2014 13:05:16 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jon Maloy <jon.maloy@...csson.com>
Cc:	Erik Hugne <erik.hugne@...csson.com>, netdev@...r.kernel.org
Subject: Re: skb_try_coalesce bug?

On Tue, 2014-04-22 at 15:38 -0400, Jon Maloy wrote:

> 
> In the case I encountered, our head buffer is linear (skb->data_len == 0),
> so it is the real tailroom value that is returned. An alas, that one is big
> enough to contain the last (small) fragment of the message.

Whole point of skb_try_coalesce() is to coalesce as much as possible,
without guarantee of keeping some sort of 'segments'

skb_try_coalesce - try to merge skb to prior one

If you do not want this to happen, (you seem to want nothing else in
your head buffer skb->head), you need to add some logic.

A helper temporarily setting head->tail = head->end would do it I guess.

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