netdev - Re: skb length without fragments

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Message-ID: <6b9500e2-b3eb-3c3c-3e52-d67ea0a7d51f@gmail.com>
Date:   Mon, 8 Oct 2018 11:23:05 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     pradeep kumar nalla <pradeepkumar.nalla@...il.com>,
        netdev@...r.kernel.org
Subject: Re: skb length without fragments



On 10/08/2018 11:02 AM, pradeep kumar nalla wrote:
> Hi
> 
> While testing my network driver with pktgen I could see an skb greater
> than 16K without fragments in xmit function. This lead to a fix in my
> driver that assumes when an SKB whose length is greater than 16K will
> come with fragments. Apart from pktgen what are the chances or
> possibilities of getting an SKB greater than 16K without fragments? .
> When I tried with tools like iperf/iper3/netperf, didn’t see a single
> incidence where the SKB length is greater than 16K and without frags.
> Even socket layer I see function alloc_skb_with_frags, does this mean
> all the larger packets come with frags.
>

There are cases where skb_linearize() calls happen, and then certainly
can feed a driver with a big linear skb.

Even if current tree would not hit this, you have to play safe and
do the check in the driver.