Re: [PATCH v2 4/7] login: Add 64-bit time support to utmp/utmpx

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 05/08/2020 16:28, Joseph Myers wrote:
> On Wed, 5 Aug 2020, Adhemerval Zanella via Libc-alpha wrote:
> 
>>   - New file names are defined for _PATH_UTMP, _PATH_WTMP, and
>>     _PATH_UTMP_DB (if applicable) and used as default for the new 2.33
>>     utmp{x} symbols.
> 
> On architectures that already have 64-bit time in these files, I think it 
> would be best to keep the same names as at present (and likewise for 
> lastlog).  (I'm not particularly concerned with whether such architectures 
> get (unnecessary) new symbol versions, though ideally we'd avoid code size 
> increase by ensuring there is no translation logic.)  If any such 
> architectures are using a different layout from the new generic one, 
> despite using 64-bit times, maybe they could keep their own version of the 
> layout to avoid needing multiple versions of the files?
> 
> Additions to the NEWS file are also needed to discuss these changes and 
> what distributions should do on glibc upgrade.
> 

I thought keeping the same filename for architectures that already
have 64-bit ut_tv member.  However, currently only s390 fits in this
category and it would make it an outlier.  It means that glibc on s390
would be the only ABI with a different _PATH_UTMP than the default one,
which I see only adds extra complexity in the transition (distro would
need to handle s390 as an exception, this will need to be properly
documented not only in glibc, it will require an arch-specific s390
path.h). 

I am not really against keep the same _PATH_UTMP and _PATH_WTMP, but
I think keeping arch-neutral tends to cause less confusion (which I 
foresee it would happen with this change anyway).

Regarding the new symbols versions, the patch already handles it 
for s390: neither on s390 nor on s390x new symbols are created.  And
utmp{x} layout is also preserved (the ABI has arch-specific 
struct_utmp.h and struct_utmpx.h). The only change is indeed new
_PATH_UTMP and _PATH_WTMP names.

I will work on a NEWS entry.