[ovs-dev] [PATCH 5/8] datapath: Add support for tunnel fragmentation.

Ben Pfaff blp at nicira.com
Wed Aug 18 16:49:55 UTC 2010

On Wed, Aug 18, 2010 at 12:08:49AM -0700, Jesse Gross wrote:
> Up until now it was assumed that encapsulated packets larger than
> the MTU would be fragmented by the IP stack.  However, some
> tunneling protocols provide their own fragmentation mechanism.  This
> adds the necessary support to the generic tunnel code to support
> fragmentation.
> Signed-off-by: Jesse Gross <jesse at nicira.com>

It seems totally bizarre to me that "local_df" is set to 1 to *allow*
fragmentation.  I never would have guessed without the comment that you
added (which is not new in this patch).

The build_header member in struct tnl_ops could use a comment.

get_random_bytes() is pretty expensive.  Most of the network stack uses
net_random() or random32() (same thing), can you use that instead?

It's hard to evaluate the use of the new 'frag_id' member of struct
tnl_vport, since it's treated as write-only in this commit.  atomic_t's
are relatively expensive on SMP, but maybe fragmentation is inherently
expensive enough that it doesn't matter?

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