Re: [PATCH] waitid system call

From: Michael Kerrisk
Date: Wed Sep 01 2004 - 06:32:24 EST

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Just for completeness, I've updated the table below to include
the AIX 5.2 result fro Eric Dumazet, and a Unixware result
that I've also now got. Unixware is like most other
implementations, in zeroing out the siginfo_t structure
when WNOHANG has no waitable children.

Cheers,

Michael

Linux Tru64 Solaris HP-UX Irix AIX U/Ware
2.6.8.1 5.1 8 11 6.5 5.2
+waitid
si_pid y. y* y* y y* y. y*
si_uid y. n* [1] n* [2] n [1] n* n. n*
si_signo y. y* y* y y* y. y*
si_status y. y* y* y y# y. y*
si_code y. y* y* y y* y. y*
si_errno ?. ?* ?* ? ?* ?. ?*
si_stime n. n* y* [3] - n# - -
si_utime n. n* y* [3] - n* - -

Key
---

The first character in each table cell indicates whether
waitid() sets the field on this platform:

y this field is set on this platform

n this field is not set on this platform

? there is insufficient information to determine if
this field is meaningfully set on this platform

- this field is not available on this platform

NOTE: The given test does not reveal whether si_errno is
meaningfully set on any platform (and I haven't
examined the header files sufficiently closely
enough to check if any further details can be
determined). Offhand, I can't think of any
circumstances where it could be meaningful with
waitid().)

The second character in each table cell indicates (if present)
how the field is treated when a WNOHANG operation is performed
and there is no child in a waitable state

. the field is left unchanged

* the field is explicitly initialized to 0

NOTE: the Linux behaviour has now changed with the
more recent patch that DOES zero out the fields when
WNOHANG has no waitable children.

# the field is initialized to some random value
(i.e., something I don't understand)

NOTE: WNOHANG is broken on HP/UX 11 ? if there are no
children that have yet terminated, waitid() fails
with the error ECHILD.

Notes to table:

[1] On Tru64 5.1 and HP-UX 11, si_uid is not meaningful,
but coincides with si_status, so a value is filled in.

[2] On Solaris 8, si_uid is not meaningful, but coincides with
si_utime, so a value is filled in.

[3] On Solaris 8, the si_stime and si_utime fields
return values in centiseconds.

Summary points
--------------

1. On most other implementations (other than AIX), when WNOHANG
is specified, all fields of the siginfo_t structure are
returned zeroed out if no child is in a waitable state,
with the following exceptions:

WNOHANG on HP-UX is broken as noted above.

On Irix 6.5, si_status and si_stime are filled in
with some unexplained values; the remaining fields
are zeroed out.

2. All waitpid() implementations support si_pid, si_signo,
si_status, and si_code.

3. Only Linux supports si_uid (and the rusage fields, which
weren't employed in this test).

4. Solaris is the only implementation that supports
si_stime and si_utime.

Actual runs on the various platforms are shown below.

Cheers,

Michael

===========

Linux 2.6.8.1 + waitid patch

$ ./a.out escHi 1 3
Linux tekapo 2.6.8.1 #1 Wed Aug 18 11:04:01 CEST 2004 i686 i686 i386
GNU/Linux
child 1 PID=8208 started
child 2 PID=8209 started
0.04: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
si_stime=99; si_utime=99;
0.54: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
si_stime=99; si_utime=99;
child 1 PID=8208 finished
1.04: waitid() returned 0
si_pid=8208; si_uid=500; si_signo=17;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=99; si_utime=99;
1.55: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
si_stime=99; si_utime=99;
2.05: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
si_stime=99; si_utime=99;
2.55: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
si_stime=99; si_utime=99;
child 2 PID=8209 finished
3.05: waitid() returned 0
si_pid=8209; si_uid=500; si_signo=17;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=99; si_utime=99;
3.55: waitid: No child processes

===========

Tru64 5.1

[I have no explanation for the odd si_errno setting on the
first call below.]

$ ./a.out escHi 1 3
OSF1 spe206.testdrive.hp.com V5.1 2650 alpha
child 1 PID=1884812 started
0.01: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=-1024;
si_stime=0; si_utime=0;
child 2 PID=1885104 started
0.53: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
child 1 PID=1884812 finished
1.03: waitid() returned 0
si_pid=1884812; si_uid=22; si_signo=20;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=0; si_utime=0;
1.53: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
2.03: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
2.53: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
child 2 PID=1885104 finished
3.03: waitid() returned 0
si_pid=1885104; si_uid=22; si_signo=20;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=0; si_utime=0;
3.54: waitid: No child processes

===========

HP-UX 11

[WNOHANG is broken on this platform]

$ ./a.out escHi 1 3
HP-UX spe192 B.11.11 U 9000/800 1839940656 unlimited-user license
child 2 PID=5729 started
child 1 PID=5728 started
0.03: waitid: No child processes
$ child 1 PID=5728 finished
child 2 PID=5729 finished

./a.out esci 1 3
HP-UX spe192 B.11.11 U 9000/800 1839940656 unlimited-user license
child 1 PID=5733 started
child 2 PID=5734 started
child 1 PID=5733 finished
1.01: waitid() returned 0
si_pid=5733; si_uid=22; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
child 2 PID=5734 finished
3.01: waitid() returned 0
si_pid=5734; si_uid=22; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
3.01: waitid: No child processes

===========

Solaris 8

$ ./a.out escHi 1 3
SunOS sunbode6 5.8 Generic_108528-14 sun4u sparc SUNW,Ultra-4
child 1 PID=20682 started
0.02: child 2 PID=20683 started
waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
0.52: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
child 1 PID=20682 finished
1.03: waitid() returned 0
si_pid=20682; si_uid=80; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=20; si_utime=80;
1.54: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
2.05: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
2.56: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
si_stime=0; si_utime=0;
child 2 PID=20683 finished
3.07: waitid() returned 0
si_pid=20683; si_uid=239; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=61; si_utime=239;
3.58: waitid: No child processes

===========

Irix 6.5

$ ./a.out escHi 1 3
IRIX64 max 6.5 04091957 IP30
child 1 PID=62684 started
child 2 PID=62704 started
0.04: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=809598976; si_code=0 (????); si_errno=0;
si_stime=-1476395008; si_utime=0;
0.59: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=4; si_code=0 (????); si_errno=0;
si_stime=-1476395008; si_utime=0;
child 1 PID=62684 finished
1.10: waitid() returned 0
si_pid=62684; si_uid=0; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=0; si_utime=0;
1.61: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=4; si_code=0 (????); si_errno=0;
si_stime=-1476395008; si_utime=0;
2.12: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=4; si_code=0 (????); si_errno=0;
si_stime=-1476395008; si_utime=0;
2.63: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=4; si_code=0 (????); si_errno=0;
si_stime=-1476395008; si_utime=0;
child 2 PID=62704 finished
3.14: waitid() returned 0
si_pid=62704; si_uid=0; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
si_stime=0; si_utime=0;
3.65: waitid: No child processes

===========

AIX 5.2

# ./waitid_test escHi 1 3
AIX aix610p-ref 2 5 005FD96A4C00
child 1 PID=25204 started
child 2 PID=26944 started
0.03: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
0.53: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
child 1 PID=25204 finished
1.03: waitid() returned 0
si_pid=25204; si_uid=0; si_signo=20;
si_status=22; si_code=10 (CLD_EXITED); si_errno=0;
1.53: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
2.03: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
2.53: waitid() returned 0
si_pid=99; si_uid=99; si_signo=99;
si_status=99; si_code=99 (????); si_errno=99;
child 2 PID=26944 finished
3.03: waitid() returned 0
si_pid=26944; si_uid=0; si_signo=20;
si_status=22; si_code=10 (CLD_EXITED); si_errno=0;
3.53: waitid: No child processes

===
Unixware

$ ./a.out escHi 1 3

UNIX_SV shaft 4.2MP 2.1.1 i386 x86at
0.03: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
child 2 PID=13756 started
child 1 PID=13755 started
0.53: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
1.03: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
child 1 PID=13755 finished
1.53: waitid() returned 0
si_pid=13755; si_uid=0; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
2.03: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
2.53: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
3.03: waitid() returned 0
si_pid=0; si_uid=0; si_signo=0;
si_status=0; si_code=0 (????); si_errno=0;
child 2 PID=13756 finished
3.53: waitid() returned 0
si_pid=13756; si_uid=0; si_signo=18;
si_status=22; si_code=1 (CLD_EXITED); si_errno=0;
4.03: waitid: No child processes

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