On Mon, Nov 27, 2017 at 11:59 AM, Jiri Pirko jiri@resnulli.us wrote:
Mon, Nov 27, 2017 at 05:19:25PM CET, arnd@arndb.de wrote:
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
[...]
@@ -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.