-----Original Message-----
From: Jan Beulich [mailto:JBeulich@suse.com]
Sent: 27 February 2014 12:20
To: Paul Durrant
Cc: davem@davemloft.net; Eric Dumazet; netdev@vger.kernel.org
Subject: RE: [PATCH net-next] consolidate duplicate code is
skb_checksum_setup() helpers

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On 27.02.14 at 13:00, Paul Durrant [off-list ref] wrote:

 -----Original Message-----
From: Jan Beulich [mailto:JBeulich@suse.com]
Sent: 27 February 2014 11:50
To: Paul Durrant
Cc: davem@davemloft.net; Eric Dumazet; netdev@vger.kernel.org
Subject: RE: [PATCH net-next] consolidate duplicate code is
skb_checksum_setup() helpers

quoted

quoted

quoted

On 27.02.14 at 11:57, Paul Durrant [off-list ref] wrote:

 -----Original Message-----
From: Jan Beulich [mailto:JBeulich@suse.com]
Sent: 27 February 2014 09:05
To: netdev@vger.kernel.org
Cc: Paul Durrant; davem@davemloft.net; Eric Dumazet
Subject: [PATCH net-next] consolidate duplicate code is
skb_checksum_setup() helpers

Realizing that the skb_maybe_pull_tail() calls in the IP-protocol
specific portions of both helpers are terminal ones (i.e. no further
pulls are expected), their maximum size to be pulled can be made

match

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their minimal size needed, thus making the code identical and hence
possible to be moved into another helper.

There is a difference in the case of an IPv4 TCP packet with options.

With

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your patch it will only get pulled up as far as the base header so there

may

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need to be another pull for options parsing.

Don't the options start right after the IP header, before the TCP
or UDP one? In which case the pull covers them.

*IP* options do, TCP options are immediately after the TCP header (hence

the

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TCP header length field). UDP doesn't have options.

Oh, right, of course. But then again - is the maximum length of
TCP options different between v4 and v6? If not, that limit
should be used here rather than the more generic (and version
dependent) IP limit.

I don't know off the top of my head - I'd have to go look. My hunch is that TCP options are essentially independent of IP version. Anyway, the header is limited to 60 bytes max due to the 4 bit width of the header length field so you may as well just use that.

And iiuc the UDP case could remain as is.

Yep.

  Paul