Re: [PATCH v4] linux: Fix ancillary 64-bit time timestamp conversion (BZ #28349, BZ #28350)

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella:

>> Are you sure?  I think our current recvmsg implementation cannot tell
>> these two cases apart:
>> 
>>   (a) time64 application running on an old kernel that does not have
>>       time64 timestamping support (so time32 setsockopt was used by
>>       glibc)
>> 
>>   (b) time32 application running on any kernel that uses time32
>>       setsockopt
>> 
>> In both cases, we generate the time64 timestamp, and that can use to
>> MSG_CTRUNC.  This is the systemd failure.
>> 
>>   DHCP6 broken on armhf (and probably other 32 bit arches)
>>   <https://github.com/systemd/systemd/issues/20564>
>> 
>> We can fix this in a follow-up patch.
>
> The MSG_CTRUNC is suppose to be an warning to application would need a large
> buffer for (a), it does not really make sense for (b).  I think we can
> improve by adding a recvmsg64 that calls __convert_scm_timestamps and
> remove the conversion on time32 call.

Right, I expected something like that, which is why I insisted on adding
the time64 symbol aliases.

> It would still need a large buffer for (a), but I expect that time64
> applications that expects to run on older kernels would need to handle
> it.

Sounds reasonable to me.

Thanks,
Florian