Re: [RFC v2] system_data_types.7: Draft v2

Michael Kerrisk (man-pages)
2020-09-14T15:04:01Z

Hi Alex,

On 9/14/20 4:03 PM, Alejandro Colomar wrote:
> Changelog since Draft v1:
>
> - Fix includes for timer_t: remove <time.h>
> - tfix
> - Clarify POSIX requirements
> - Remove subsections, and instead use full names for structs/unions

Small misunderstanding here, bu the way. I meant: after merging
the lists, sort by identifier name. Thus:

union sigval
suseconds_t
time_t
timer_t
struct timespec
struct timeval

> - Includes: ffix
> - Conforming to: ffix
> - struct timespec: update "see also"
> - Add suseconds_t
> - Remove old comments
>
> Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
> ---
>
> Hi Michael,
>
> On 2020-09-14 12:37, Michael Kerrisk (man-pages) wrote:
>> Good. I think that we can get away with just mentioning one each of
>> POSIX.1-200x and Cxx, with the latter starting at C99. I think C89 is
>> far enough back in time that we don't need to clutter the page with
>> it. Something like:
>>
>> Conforming to: C99 and later; POSIX.1-2001 and later.
>
> OK.
>
>> Instead, I looked inside the pages that you listed to see which APIs
>> seemed "relevant".
>
> Work in progress. I'll do it for the other types soon.

Okay. I'll make a few notes below.

>> You better include suseconds_t in the next draft:-).
>
> :-)
>
>> Having seen how it looks with the header files, I'm going to suggest a
>> differnt approach. Let's put them on a separate line, something like:
>>
>> Obtained by including: <abc.h> or <xyz.h>
>
> I simplified it to just:
>
> Include: <asd.h> or <qwe.h>

Yes, better.

>> It's an open question whether the links should be in section 3 or
>> section 7. Do you have any thoughts on what's better?
>
> All sources I could find talk about section 3 as a section containing
> all C "library functions".
> Types don't exactly fit in that description, but it could be stretched
> a bit to contain all C "library definitions".
>
> Also, libbsd already chose section 3, and I don't see a strong reason
> against it, so maybe we could follow that pattern.

Thanks. I forgot that libbsd detail. Yes, let's go with Section 3.

> I would still have system_data_types.7 in section 7, as it doesn't
> match the name of any library definition.

Yes.

> BTW, would you also add "struct-" and "union-" link pages?:
>
> man3/struct-timespec.3 | 1 +
> man3/timespec.3 | 1 +
>
> instead of
>
> man3/timespec.3 | 1 +

I think just one link: the name of the type (without any
"struct" or "union")

>> Don't get wrapped up in including too many more types in the
>> yet, while we try to iron out the format.
>>
>> Also, I'd like to see the types added incrementally (one or a few
>> at a time), so that it's easy to comment on each type, when needed.
>
> Agree.
>
> Thanks,
>
> Alex

A few further comments below.
>
> man3/sigval.3 | 1 +
> man3/suseconds_t.3 | 1 +
> man3/time_t.3 | 1 +
> man3/timer_t.3 | 1 +
> man3/timespec.3 | 1 +
> man3/timeval.3 | 1 +
> man7/system_data_types.7 | 227 +++++++++++++++++++++++++++++++++++++++
> 7 files changed, 233 insertions(+)
> create mode 100644 man3/sigval.3
> create mode 100644 man3/suseconds_t.3
> create mode 100644 man3/time_t.3
> create mode 100644 man3/timer_t.3
> create mode 100644 man3/timespec.3
> create mode 100644 man3/timeval.3
> create mode 100644 man7/system_data_types.7
>
> diff --git a/man3/sigval.3 b/man3/sigval.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/sigval.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man3/suseconds_t.3 b/man3/suseconds_t.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/suseconds_t.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man3/time_t.3 b/man3/time_t.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/time_t.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man3/timer_t.3 b/man3/timer_t.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/timer_t.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man3/timespec.3 b/man3/timespec.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/timespec.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man3/timeval.3 b/man3/timeval.3
> new file mode 100644
> index 000000000..db50c0f09
> --- /dev/null
> +++ b/man3/timeval.3
> @@ -0,0 +1 @@
> +.so man7/system_data_types.7
> diff --git a/man7/system_data_types.7 b/man7/system_data_types.7
> new file mode 100644
> index 000000000..8b89a46f3
> --- /dev/null
> +++ b/man7/system_data_types.7
> @@ -0,0 +1,227 @@
> +.\" Copyright (c) 2020 by Alejandro Colomar <colomar.6.4.3@gmail.com>
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" Permission is granted to make and distribute verbatim copies of this
> +.\" manual provided the copyright notice and this permission notice are
> +.\" preserved on all copies.
> +.\"
> +.\" Permission is granted to copy and distribute modified versions of this
> +.\" manual under the conditions for verbatim copying, provided that the
> +.\" entire resulting derived work is distributed under the terms of a
> +.\" permission notice identical to this one.
> +.\"
> +.\" Since the Linux kernel and libraries are constantly changing, this
> +.\" manual page may be incorrect or out-of-date. The author(s) assume no
> +.\" responsibility for errors or omissions, or for damages resulting from
> +.\" the use of the information contained herein. The author(s) may not
> +.\" have taken the same level of care in the production of this manual,
> +.\" which is licensed free of charge, as they might when working
> +.\" professionally.
> +.\"
> +.\" Formatted or processed versions of this manual, if unaccompanied by
> +.\" the source, must acknowledge the copyright and authors of this work.
> +.\" %%%LICENSE_END
> +.\"
> +.\"
> +.TH SYSTEM_DATA_TYPES 7 2020-09-13 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +system_data_types \- overview of system data types
> +.SH DESCRIPTION
> +.\" TODO:
> +.\" * Add types
> +.\" * Check specific POSIX "Conforming to" versions
> +.\" * Correctly highlight function names and similar (see timer_t)
> +.TP
> +.BI "struct " timespec
> +.IP
> +Include:
> +.I <time.h>
> +.IP
> +.EX
> +struct timespec {
> + time_t tv_sec; /* Seconds */
> + long tv_nsec; /* Nanoseconds */
> +};
> +.EE
> +.IP
> +Describes times in seconds and nanoseconds.
> +.IP
> +Conforming to: C11 and later; POSIX.1-xxxx and later.
> +.IP
> +See also:
> +.\".BR clock_getres (2),
> +.BR clock_gettime (2),
> +.BR clock_nanosleep (2),
> +.\".BR futex (2),
> +.\".BR io_getevents (2),
> +.BR nanosleep (2),
> +.\".BR poll (2),
> +.\".BR recvmmsg (2),
> +.\".BR sched_rr_get_interval (2),
> +.\".BR select (2),
> +.\".BR semop (2),
> +.\".BR sigwaitinfo (2),
> +.\".BR stat (2),
> +.\".BR timerfd_create (2),
> +.BR timerfd_gettime (2),
> +.BR timer_gettime (2)
> +.\".BR timer_settime (2),
> +.\".BR utimensat (2),
> +.\".BR aio_suspend (3),
> +.\".BR clock_getcpuclockid (3),
> +.\".BR getaddrinfo_a (3),
> +.\".BR mq_receive (3),
> +.\".BR mq_send (3),
> +.\".BR pthread_getcpuclockid (3),
> +.\".BR pthread_tryjoin_np (3),
> +.\".BR sem_wait (3),
> +.\".BR socket (7)
> +.TP
> +.BI "struct " timeval
> +.IP
> +Include:
> +.I <sys/time.h>

or <sys/select.h>
(Really, a PDF copy of the standard is gpoing to help...)

> +.IP
> +.EX
> +struct timeval {
> + time_t tv_sec; /* Seconds */
> + suseconds_t tv_usec; /* Microseconds */
> +};
> +.EE
> +.IP
> +Describes times in seconds and microseconds.

According to POSIX, this shall be a signed integer type.

> +.IP
> +Conforming to: POSIX.1-xxxx and later.
> +.IP
> +See also:

I think there are several in the following list that should be removed...

> +.BR adjtimex (2),
> +.BR futimesat (2),
> +.BR getitimer (2),
> +.BR getpriority (2),
> +.BR getrusage (2),
> +.BR gettimeofday (2),
> +.BR select (2),
> +.BR syscall (2),
> +.BR syscalls (2),
> +.BR utime (2),
> +.BR wait4 (2),
> +.BR adjtime (3),
> +.BR futimes (3),
> +.BR ntp_gettime (3),
> +.BR rpc (3),
> +.BR rtime (3),
> +.BR timeradd (3),
> +.BR utmp (5),
> +.BR packet (7),
> +.BR socket (7)
> +.TP
> +.I suseconds_t
> +.IP
> +Include:
> +.I <sys/types.h>
> +.IP
> +Used for time in microseconds.
> +It shall be a signed integer type

s/It/According to POSIX, it/

> +capable of storing values at least in the range [-1, 1000000].
> +.IP
> +Conforming to: POSIX.1-xxxx and later.
> +.IP
> +See also:
> +.\".BR getitimer (2),
> +.\".BR gettimeofday (2),
> +.\".BR select (2),
> +.\".BR adjtime (3),
> +.\".BR ntp_gettime (3),
> +.BR timeval (3)
> +.\".BR timeradd (3)

The above is a little too circular for my taste :-).

How about just saying:

[[
This type is used for one of the
fields of the timeval structure (see below).
]]

> +.TP
> +.I time_t
> +.IP
> +Include:
> +.I <time.h>
> +or
> +.I <sys/types.h>
> +.IP
> +Used for time in seconds.
> +In POSIX, it shall be an integer type.

s/In/According to/

> +.IP
> +Conforming to: C99 and later; POSIX.1-xxxx and later.
> +.IP
> +See also:

Many items in the following list should go...

> +.BR clock_getres (2),
> +.BR clock_nanosleep (2),
> +.BR getitimer (2),
> +.BR gettimeofday (2),
> +.BR io_getevents (2),
> +.BR keyctl (2),
> +.BR msgctl (2),
> +.BR msgop (2),
> +.BR nanosleep (2),
> +.BR sched_rr_get_interval (2),
> +.BR select (2),
> +.BR semctl (2),
> +.BR shmctl (2),
> +.BR stat (2),
> +.BR stime (2),
> +.BR time (2),
> +.BR timerfd_create (2),
> +.BR timer_settime (2),
> +.BR times (2),
> +.BR utime (2),
> +.BR utimensat (2),
> +.BR adjtime (3),
> +.BR ctime (3),
> +.BR difftime (3),
> +.BR ftime (3),
> +.BR mq_receive (3),
> +.BR mq_send (3),
> +.BR newlocale (3),
> +.BR ntp_gettime (3),
> +.BR pthread_cleanup_push (3),
> +.BR pthread_tryjoin_np (3),
> +.BR rtime (3),
> +.BR sem_wait (3),
> +.BR strcat (3),
> +.BR strftime (3),
> +.BR timegm (3),
> +.BR timeradd (3)
> +.TP
> +.I timer_t
> +.IP
> +Include:

Add "<time.h> or"

> +.I <sys/types.h>
> +.IP
> +Used for timer ID returned by timer_create().
> +There are no defined comparison or assignment operators for this type.

Where is that mentioned in the standard, by the way?

> +.IP
> +Conforming to: POSIX.1-xxxx and later.
> +.IP
> +See also:
> +.BR timer_create (2),
> +.BR timer_delete (2),
> +.BR timer_getoverrun (2),
> +.BR timer_settime (2)
> +.TP
> +.BI "union " sigval
> +.IP
> +Include:
> +.I <signal.h>
> +.IP
> +.EX
> +union sigval {
> + int sigval_int; /* Integer value */
> + void *sigval_ptr; /* Pointer value */
> +};
> +.EE
> +.IP
> +Data passed with notification.

s/notification/a signal/

> +.IP
> +Conforming to: POSIX.1-xxxx and later.
> +.IP
> +See also:
> +.BR rt_sigqueueinfo (2),
> +.BR sigaction (2),
> +.BR mq_notify (3),
> +.BR pthread_sigqueue (3),
> +.BR sigqueue (3),
> +.BR sigevent (7)

Thanks,

Michael

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/