Re: [PATCH] Fix the man page

[Alejandro Colomar <alx@kernel.org>]

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Hi Zijun,

On 2023-06-20 20:21, Zijun Zhao wrote:
> Hi Alejandro,
>   I already created the patch attached below. How to add it to this
> page? Do I need to use git push, or just provide the patch? Could you
> help put it in .SH VERSIONS? Thank you!
> Best,
> Zijun Zhao

I've applied the patch.

(You just need to provide the patch, as you did.  I apply and push it.)

Thanks!
Alex

> 
> On Fri, May 19, 2023 at 3:42 PM Alejandro Colomar
> <alx.manpages@gmail.com> wrote:
>>
>> On 5/20/23 00:21, enh wrote:
>>> On Fri, May 19, 2023 at 1:03 AM Alejandro Colomar
>>> <alx.manpages@gmail.com> wrote:
>> [...]
>>
>>>> You'll also need to add _Nullable to the function prototypes in the
>>>> SYNOPSIS.
>>>
>>> heh, funnily enough, zijunzhao's adding exactly those annotations to
>>> the bionic headers, which is how we stumbled across this.
>>
>> :)
>>
>>>
>>>> BTW, I see that glibc still requires nonnull in gettimeofday(3).  It's
>>>> only settimeofday(3) that is nullable.
>>>
>>> yeah, but the _kernel_ allows null in both (see kernel/time/time.c),
>>> and this is section 2 of the man page. it's unclear to me whether
>>> that's worth calling out up here, or should be down in the
>>> Linux-specific section? (this page seems to be written as if it cares
>>> about Hurd? "On a non-Linux kernel, with glibc ...".)
>>
>> Yes, we care about hurd, and non-g libc, in this page and others.
>> Normally, I would be cautious, and specify the strictest prototype of
>> all implementations about which I care, but in this case, glibc seems
>> unnecessarily restrictive, and I'm ready to add _Nullable if the kernel
>> and some libc support that.  However, as a caution, please add a
>> (CAVEATS?) section documenting that glibc doesn't allow NULL there.
>> Or maybe keep the SYNOPSIS without _Nullable, and have some VERSIONS
>> section specifying that other libcs and the kernel support NULL.
>>
>>>
>>>> See:
>>>>
>>>>
>>>> $ grepc gettimeofday /usr/include/*/sys/time.h
>>>> /usr/include/x86_64-linux-gnu/sys/time.h:67:
>>>> extern int gettimeofday (struct timeval *__restrict __tv,
>>>>                          void *__restrict __tz) __THROW __nonnull ((1));
>>>>
>>>>
>>>> /usr/include/x86_64-linux-gnu/sys/time.h:75:
>>>> #  define gettimeofday __gettimeofday64
>>>>
>>>>
>>>> $ grepc settimeofday /usr/include/*/sys/time.h
>>>> /usr/include/x86_64-linux-gnu/sys/time.h:86:
>>>> extern int settimeofday (const struct timeval *__tv,
>>>>                          const struct timezone *__tz)
>>>>       __THROW;
>>>>
>>>>
>>>> /usr/include/x86_64-linux-gnu/sys/time.h:106:
>>>> #   define settimeofday __settimeofday64
>>>>
>>>>
>>>> And while NULL may be non-UB, the manual page is not very clear on why
>>>> someone would want to call these functions with NULL.  Could you
>>>> please also explain why would someone want to call these functions
>>>> with NULL?  (Let's discuss it in the list, and then we see what
>>>> wording we use for the page.)
>>>
>>> so there are definitely several orders of magnitude more users of a
>>> null timezone --- most callers don't want that (not least because
>>> glibc seems to not fill it out anyway? musl certainly doesn't,
>>> implementing gettimeofday() in terms of clock_gettime() instead).
>>>
>>> the users for a null time (and non-null timezone; i haven't seen
>>> anyone -- not even a test -- pass null for both!) are interesting.
>>> Android's init uses settimeofday() with only a timezone, but --
>>> although the timezone to use is settable in device-specific init
>>> scripts -- for devices in our tree, that's actually always 0. there's
>>> other proprietary (non-Google) code that uses gettimeofday() with only
>>> a timezone, and i'm honestly not sure whether it's deliberate that
>>> it's asking the _kernel_ for the timezone or not (i'm guessing they
>>> want the device timezone rather than the app timezone, but i do not
>>> believe there are devices where the _kernel_ timezone matches the
>>> device timezone?). certainly both of these use cases seem worth
>>> following up on, and i will do.
>>
>> Please.  And thanks for the details!
>>
>>>
>>> but looking at musl (which ignores tz in both cases) it seems like the
>>> most impactful change would be to fix "The functions gettimeofday()
>>> and settimeofday() can get and set the time as well as a timezone" :-)
>>
>> :-)
>>
>> Makes sense; although it would be worth being clear about if that's
>> really true, and if libcs do support that as well as the kernel.
>>
>>>
>>> it also seems like an improvement to really call out the libc/kernel
>>> differences more clearly though.
>>
>> Sure.  Many pages have a dedicated subsection.  Feel free to add it
>> to this page.  I'd put it in .SH VERSIONS.
>>
>> $ grep -rn 'C library/kernel differences' man*
>> man2/sigprocmask.2:120:.SS C library/kernel differences
>> man2/setreuid.2:168:.SS C library/kernel differences
>> man2/brk.2:126:.SS C library/kernel differences
>> man2/sigwaitinfo.2:114:.SS C library/kernel differences
>> man2/gethostname.2:122:.SS C library/kernel differences
>> man2/getcpu.2:73:.SS C library/kernel differences
>> man2/fork.2:263:.SS C library/kernel differences
>> man2/epoll_wait.2:258:.SS C library/kernel differences
>> man2/wait4.2:157:.SS C library/kernel differences
>> man2/stat.2:355:.SS C library/kernel differences
>> man2/sigsuspend.2:74:.SS C library/kernel differences
>> man2/access.2:40:                /* But see C library/kernel differences, below */
>> man2/access.2:285:.SS C library/kernel differences
>> man2/clock_getres.2:354:.SS C library/kernel differences
>> man2/getpid.2:57:.SS C library/kernel differences
>> man2/setfsgid.2:57:.SS C library/kernel differences
>> man2/getgroups.2:142:.SS C library/kernel differences
>> man2/sigaction.2:946:.SS C library/kernel differences
>> man2/setresuid.2:100:.SS C library/kernel differences
>> man2/readv.2:290:.SS C library/kernel differences
>> man2/readv.2:342:.SS Historical C library/kernel differences
>> man2/open.2:1393:.SS C library/kernel differences
>> man2/setgid.2:58:.SS C library/kernel differences
>> man2/setfsuid.2:97:.SS C library/kernel differences
>> man2/ptrace.2:2814:.SS C library/kernel differences
>> man2/poll.2:382:.SS C library/kernel differences
>> man2/sigreturn.2:130:.SS C library/kernel differences
>> man2/eventfd.2:267:.SS C library/kernel differences
>> man2/mmap.2:729:.SS C library/kernel differences
>> man2/_exit.2:104:.SS C library/kernel differences
>> man2/time.2:86:.SS C library/kernel differences
>> man2/pread.2:101:.SS C library/kernel differences
>> man2/seccomp.2:975:.IR "C library/kernel differences" .
>> man2/setuid.2:104:.SS C library/kernel differences
>> man2/sched_setaffinity.2:95:return 0 (but see "C library/kernel differences" below,
>> man2/sched_setaffinity.2:220:.SS C library/kernel differences
>> man2/select.2:559:.SS C library/kernel differences
>> man2/sigpending.2:52:.SS C library/kernel differences
>> man2/posix_fadvise.2:135:.SS C library/kernel differences
>> man2/gettimeofday.2:173:.SS C library/kernel differences
>> man2/uname.2:83:.SS C library/kernel differences
>> man2/clone.2:1576:.SS C library/kernel differences
>> man2/getpriority.2:185:.SS C library/kernel differences
>> man2/signalfd.2:331:.SS C library/kernel differences
>> man2/timer_create.2:225:.SS C library/kernel differences
>> man2/wait.2:464:.SS C library/kernel differences
>> man2/nice.2:80:.SS C library/kernel differences
>> man2/chmod.2:303:.SS C library/kernel differences
>> man2/seteuid.2:114:.SS C library/kernel differences
>> man3/getcwd.3:217:.SS C library/kernel differences
>> man3/killpg.3:98:.SS C library/kernel differences
>> man3/mq_notify.3:174:.SS C library/kernel differences
>> man3/mq_open.3:269:.SS C library/kernel differences
>> man3/sigqueue.3:118:.SS C library/kernel differences
>> man3type/epoll_event.3type:37:.SS C library/kernel differences
>> man7/man-pages.7:402:.I "C library/kernel differences"
>>
>> Cheers,
>> Alex
>>
>>>
>>>> Thanks!
>>>> Alex
>>>>
>>>> --
>>>> <http://www.alejandro-colomar.es/>
>>>> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
>>>>
>>
>> --
>> <http://www.alejandro-colomar.es/>
>> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5

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