[ovs-dev] [PATCH] ofp-actions: Don't encode variable length fields using NXAST_REG_LOAD.

Jesse Gross jesse at nicira.com
Fri Aug 28 18:26:42 UTC 2015

On Fri, Aug 28, 2015 at 11:15 AM, Ben Pfaff <blp at nicira.com> wrote:
> On Thu, Aug 27, 2015 at 07:06:51PM -0700, Jesse Gross wrote:
>> Currently, when using an OpenFlow 1.0 connection to encode a
>> tunnel metadata set field action, a series of NXAST_REG_LOADs
>> are emitted. The result is something like this:
>> actions=load:0xa->NXM_NX_TUN_METADATA0[0..63],load:0->
>> NXM_NX_TUN_METADATA0[64..127],load:0->NXM_NX_TUN_METADATA0[128..191],
>> load:0->NXM_NX_TUN_METADATA0[192..255],load:0->NXM_NX_TUN_METADATA0
>> [256..319],load:0->NXM_NX_TUN_METADATA0[320..383],load:0->
>> NXM_NX_TUN_METADATA0[384..447],load:0->NXM_NX_TUN_METADATA0[448..511],
>> load:0->NXM_NX_TUN_METADATA0[512..575],load:0->NXM_NX_TUN_METADATA0
>> [576..639],load:0->NXM_NX_TUN_METADATA0[640..703],load:0->
>> NXM_NX_TUN_METADATA0[704..767],load:0->NXM_NX_TUN_METADATA0[768..831],
>> load:0->NXM_NX_TUN_METADATA0[832..895],load:0->NXM_NX_TUN_METADATA0
>> [896..959],load:0->NXM_NX_TUN_METADATA0[960..991]
>> This happens because tunnel metadata is seen as a maximum size field
>> and so many loads need to be emitted to cover the entire thing. Besides
>> being ugly (this shows up when using ovs-ofctl in the default
>> configuration), it exposes the internal size of the field. While this
>> shouldn't be an issue since specific protocol fields (such as Geneve
>> options) have fixed max sizes even if the OVS implementation is extended,
>> it's still not a great idea.
>> If we instead use NXAST_REG_LOAD2 in cases where there isn't a suitable
>> OpenFlow alternative, both problems are avoided:
>> actions=set_field:0xa->tun_metadata0
>> This prefers NXAST_REG_LOAD2 for variable length fields since they would
>> all generally have the same problems. In addition, since the concept of
>> this type of field is fairly new, there are no backwards compatibility
>> issues.
>> Signed-off-by: Jesse Gross <jesse at nicira.com>
> Acked-by: Ben Pfaff <blp at nicira.com>

Thanks, applied to master.

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