On Mon, Nov 27, 2017 at 11:59 AM, Jiri Pirko [off-list ref] wrote:

Mon, Nov 27, 2017 at 05:19:25PM CET, arnd@arndb.de wrote:

quoted

I tried to figure out what it would take to do a version 4 mmap packet
socket interface to completely avoid the y2106 overflow problem. This is
what I came up with, reusing most of the v3 code, except for the parts
where we access the timestamps.

For kselftest, I'm adding support for testing v4 in addition to v1-v3,
but the test currently does not look at the timestamps, so it won't
check that the timestamp format actually works as intended, only that
I didn't break the parts that worked in the v3 selftest.

Overall, this is more of a mess than I expected, so it's probably not
worth doing a v4 format just for the timestamp, but the patch can serve
as a reference for anyone that needs a new format for other reasons and
fixes this along with the other changes.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---

[...]

quoted

@@ -250,7 +269,8 @@ struct tpacket_block_desc {

enum tpacket_versions {
      TPACKET_V1,
      TPACKET_V2,
-      TPACKET_V3
+      TPACKET_V3,
+      TPACKET_V4,

I wonder with how many versions are we going to eventually end up with :O

There already is an effort to come up with a new AF_PACKET V4 [1].
We should make sure that any new interface does not have the
Y2038/Y2106 issue. But, if a new version is being developed and
that subsumes all existing use cases, then there probably is no need
for another version that is a very small diff to V3.

If adding support for existing applications is useful, another approach
would be to add a new socket option that changes the semantics for
the two u32 fields in each of V1, V2 and V3 to hold nsec. Add a single
check after filling in those structs whether the option is set and, if so,
overwrite the two fields.

[1] https://lwn.net/Articles/737947/