On Fri, 11 Aug 2017 10:09:36 +0000, Jan Scheurich wrote:
Unless someone can explain to me why the datapath should understand the
internal structure/format of metadata in push_nsh, I would strongly
vote to keep the metadata as variable length octet sequence in the
non-structured OVS_ACTION_ATTR_PUSH_NSH
Could be but it still needs to be in a different attribute and not in
the ovs_action_push_nsh structure.
Separate attributes for MD1/MD2 has the advantage of easier validation:
with a separate MD1 type attribute, the size check is easier. With an
unstructured MD attribute, we'd need to look into the
OVS_ACTION_ATTR_NSH_BASE_HEADER attribute for mdtype and then validate
the unstructured MD attribute size manually. Not a big deal, though.
I don't have strong opinion here.
But I do have strong opinion that MD needs to go into a separate
attribute, whether there are separate attributes for MD1/2 or not.
Jiri
From: Jiri Benc [mailto:jbenc@redhat.com]
Sent: Friday, 11 August, 2017 12:23
On Fri, 11 Aug 2017 10:09:36 +0000, Jan Scheurich wrote:
quoted
Unless someone can explain to me why the datapath should understand the
internal structure/format of metadata in push_nsh, I would strongly
vote to keep the metadata as variable length octet sequence in the
non-structured OVS_ACTION_ATTR_PUSH_NSH
Could be but it still needs to be in a different attribute and not in
the ovs_action_push_nsh structure.
Separate attributes for MD1/MD2 has the advantage of easier validation:
with a separate MD1 type attribute, the size check is easier. With an
unstructured MD attribute, we'd need to look into the
OVS_ACTION_ATTR_NSH_BASE_HEADER attribute for mdtype and then validate
the unstructured MD attribute size manually. Not a big deal, though.
I don't have strong opinion here.
But I do have strong opinion that MD needs to go into a separate
attribute, whether there are separate attributes for MD1/2 or not.
Jiri, I am not too familiar with conventions on the OVS netlink interface regarding the handling of variable length fields. What is the benefit of structuring the push_nsh action into
OVS_ACTION_ATTR_PUSH_NSH
+-- OVS_ACTION_ATTR_NSH_BASE_HEADER
+-- OVS_ACTION_ATTR_NSH_MD
instead of grouping the base header fields and the variable length MD into a single monolithic attribute OVS_ACTION_ATTR_PUSH_NSH? Is the main concern a potential future need to add additional parameters to the push_nsh datapath action? Are there examples for such structured actions other than OVS_ACTION_ATTR_CT where the need is obvious because it is very polymorphic?
BR, Jan
BTW: The name OVS_ACTION_ATTR_NSH_BASE_HEADER is misleading because in the NSH draft the term base header is used for the first 32-bit word, whereas here it includes also the 32-bit Service Path header.