[ovs-dev] [PATCH] tunneling: Simplify path MTU discovery logic.

Ben Pfaff blp at nicira.com
Tue Feb 1 19:41:35 UTC 2011

On Thu, Jan 27, 2011 at 06:38:27PM -0800, Jesse Gross wrote:
> Previously, if path MTU discovery was disabled we would use the
> tunnel MTU instead of the underlying route's path MTU but otherwise
> still do PMTUD.  This doesn't make much sense because turning off
> PMTUD really means to not check the size of the encapsulated packets
> at all.  This removes the disconnect and simplifies the logic.
> Signed-off-by: Jesse Gross <jesse at nicira.com>

This code is very subtle.  I think it is OK now.

My compiler complains:
   datapath/linux-2.6/tunnel.c: In function 'tnl_send':
   datapath/linux-2.6/tunnel.c:1156: warning: 'frag_off' may be used uninitialized in this function

The compiler is wrong, but it could be made happy by changing frag_off
to be the return value and using a special value like -1 to indicate an
error.  That might be more readable anyway.

frag_off has only two possible values in check_mtu() now, as far as I
can tell: 0 or htons(IP_DF).  A boolean 'df' variable might be more
readable (or might not).

Acked-by: Ben Pfaff <blp at nicira.com>

More information about the dev mailing list