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Document wait6() and waitid().

Browse Source 
PR:	standards/170346
Submitted by:	"Jukka A. Ukkonen" <jau@iki.fi>
MFC after:	1 month
This commit is contained in:
Konstantin Belousov 2012-11-13 12:56:42 +00:00
parent eb3d4e1fbd
commit 0b92b54045
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=242961
2 changed files with 282 additions and 32 deletions
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3
lib/libc/sys/Makefile.inc
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@ -217,5 +217,6 @@ MLINKS+=timer_settime.2 timer_getoverrun.2 timer_settime.2 timer_gettime.2
MLINKS+=truncate.2 ftruncate.2
MLINKS+=unlink.2 unlinkat.2
MLINKS+=utimes.2 futimes.2 utimes.2 futimesat.2 utimes.2 lutimes.2
MLINKS+=wait.2 wait3.2 wait.2 wait4.2 wait.2 waitpid.2
MLINKS+=wait.2 wait3.2 wait.2 wait4.2 wait.2 waitpid.2 \
wait.2 waitid.2 wait.2 wait6.2
MLINKS+=write.2 pwrite.2 write.2 pwritev.2 write.2 writev.2

311
lib/libc/sys/wait.2
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@ -28,15 +28,17 @@
.\" @(#)wait.2 8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd November 12, 2005
.Dd November 10, 2012
.Dt WAIT 2
.Os
.Sh NAME
.Nm wait ,
.Nm waitid ,
.Nm waitpid ,
.Nm wait3 ,
.Nm wait4 ,
.Nm wait3
.Nd wait for process termination
.Nm wait6
.Nd wait for processes to change status
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
@ -46,12 +48,17 @@
.Fn wait "int *status"
.Ft pid_t
.Fn waitpid "pid_t wpid" "int *status" "int options"
.In sys/signal.h
.Ft int
.Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options"
.In sys/time.h
.In sys/resource.h
.Ft pid_t
.Fn wait3 "int *status" "int options" "struct rusage *rusage"
.Ft pid_t
.Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
.Ft pid_t
.Fn wait6 "idtype_t idtype" "id_t id" "int *status" "int options" "struct __wrusage *wrusage" "siginfo_t *infop"
.Sh DESCRIPTION
The
.Fn wait
@ -86,28 +93,172 @@ system call provides a more general interface for programs
that need to wait for certain child processes,
that need resource utilization statistics accumulated by child processes,
or that require options.
The other wait functions are implemented using
.Fn wait4 .
.Pp
The broadest interface of all functions in this family is
.Fn wait6
which is otherwise very much like
.Fn wait4
but with a few very important distinctions.
To wait for exited processes, the option flag
.Dv WEXITED
need to be explicitly specified.
This allows for waiting for processes which have experienced other
status changes without having to handle also the exit status from
the terminated processes.
Instead of the traditional
.Dv rusage
argument, a pointer to a new structure
.Bd -literal
struct __wrusage {
struct rusage wru_self;
struct rusage wru_children;
};
.Ed
can be passed.
This allows the calling process to collect resource usage statistics
from both its own child process as well as from its grand children.
When no resource usage statistics are needed this pointer can be
.Dv NULL .
The last argument
.Fa infop
must be either
.Dv NULL
or a pointer to a
.Fa siginfo_t
structure.
When specified, the structure is filled the same as for
.Dv SIGNCHLD
signal, delivered at the process state change.
.br
The process, which state is queried, is specified by two arguments
.Fa idtype
and
.Fa id .
The separate
.Fa idtype
and
.Fa id
arguments allows to support many other types of
IDs as well in addition to PID and PGID.
.Bl -bullet -offset indent
.It
If
.Fa idtype
is
.Dv P_PID ,
.Fn waitid
and
.Fn wait6
wait for the child process with a process ID equal to
.Dv (pid_t)id .
.It
If
.Fa idtype
is
.Dv P_PGID ,
.Fn waitid
and
.Fn wait6
wait for the child process with a process group ID equal to
.Dv (pid_t)id .
.It
If
.Fa idtype
is
.Dv P_ALL ,
.Fn waitid
and
.Fn wait6
wait for any child process and the
.Dv id
is ignored.
.It
If
.Fa idtype
is
.Dv P_PID
or
.Dv P_PGID
and the
.Dv id
is zero,
.Fn waitid
and
.Fn wait6
wait for any child process in the same process group as the caller.
.El
.Pp
Non-standard specifiers for the process to wait for, supported by this
implementation of
.Fn waitid
and
.Fn wait6 ,
are:
.Bl -bullet -offset indent
.It
The
.Fa idtype
value
.Dv P_UID
waits for processes which effective UID is equal to
.Dv (uid_t)id .
.It
The
.Fa idtype
value
.Dv P_GID
waits for processes which effective GID is equal to
.Dv (gid_t)id .
.It
The
.Fa idtype
value
.Dv P_SID
waits for processes which session ID is equal to
.Dv id .
In case the child process started its own new session,
SID will be the same as its own PID.
Otherwise the SID of a child process will match the caller's SID.
.It
The
.Fa idtype
value
.Dv P_JAILID
waits for processes within a jail which jail identifier is equal
to
.Dv id .
.El
.Pp
For
.Fn wait ,
.Fn wait3 ,
and
.Fn wait4
functions, the single
.Fa wpid
argument specifies the set of child processes for which to wait.
.Bl -bullet -offset indent
.It
If
.Fa wpid
is -1, the call waits for any child process.
.It
If
.Fa wpid
is 0,
the call waits for any child process in the process group of the caller.
.It
If
.Fa wpid
is greater than zero, the call waits for the process with process id
.Fa wpid .
.It
If
.Fa wpid
is less than -1, the call waits for any process whose process group id
equals the absolute value of
.Fa wpid .
.El
.Pp
The
.Fa status
@ -116,41 +267,102 @@ argument is defined below.
The
.Fa options
argument contains the bitwise OR of any of the following options.
The
.Dv WCONTINUED
option indicates that children of the current process that
.Bl -tag -width Ds
.It Dv WCONTINUED
indicates that children of the current process that
have continued from a job control stop, by receiving a
.Dv SIGCONT
signal, should also have their status reported.
The
.Dv WNOHANG
option
is used to indicate that the call should not block if
there are no processes that wish to report status.
If the
.Dv WUNTRACED
option is set,
children of the current process that are stopped
.It Dv WNOHANG
is used to indicate that the call should not block when
there are no processes wishing to report status.
.It Dv WUNTRACED
indicates that children of the current process which are stopped
due to a
.Dv SIGTTIN , SIGTTOU , SIGTSTP ,
or
.Dv SIGSTOP
signal also have their status reported.
The
.Dv WSTOPPED
option is an alias for
signal shall have their status reported.
.It Dv WSTOPPED
is an alias for
.Dv WUNTRACED .
The
.Dv WNOWAIT
option keeps the process whose status is returned in a waitable state.
.It Dv WTRAPPED
allows waiting for processes which have trapped or reached a breakpoint.
.It Dv WEXITED
indicates that the caller is wants to receive status reports from
terminated processes.
This flag is implicitly set for the functions
.Fn wait ,
.Fn waitpid ,
.Fn wait3 ,
and
.Fn wait4 .
.br
For the
.Fn waitid
and
.Fn wait6
functions, the flag has to be explicitly included in the
.Fa options ,
if status reports from terminated processes are expected.
.It Dv WNOWAIT
keeps the process whose status is returned in a waitable state.
The process may be waited for again after this call completes.
.El
.sp
For the
.Fn waitid
and
.Fn wait6
functions, at least one of the options
.Dv WEXITED ,
.Dv WUNTRACED ,
.Dv WSTOPPED ,
.Dv WTRAPPED ,
or
.Dv WCONTINUED
must be specified.
Otherwise there will be no events for the call to report.
To avoid hanging indefinitely in such a case these functions
return -1 with
.Dv errno
set to
.Dv EINVAL .
.Pp
If
.Fa rusage
is non-zero, a summary of the resources used by the terminated
process and all its
children is returned (this information is currently not available
for stopped or continued processes).
is non-NULL, a summary of the resources used by the terminated
process and all its children is returned.
.Pp
If
.Fa wrusage
argument is non-NULL, a resource usage statistics
from both its own child process as well as from its grand children
is returned.
.Pp
If
.Fa infop
is non-NULL, it must point to a
.Dv siginfo_t
structure which is filled on return such that the
.Dv si_signo
field is always
.Dv SIGCHLD
and the field
.Dv si_pid
if be non-zero, if there is a status change to report.
If there are no status changes to report and WNOHANG is applied,
both of these fields are returned zero.
When using the
.Fn waitid
function with the
.Dv WNOHANG
option set, checking these fields is the only way to know whether
there were any status changes to report, because the return value
from
.Fn waitid
is be zero as it is for any successful return from
.Fn waitid .
.Pp
When the
.Dv WNOHANG
@ -175,6 +387,20 @@ call is the same as
with a
.Fa wpid
value of -1.
The
.Fn wait6
call, with the bits
.Dv WEXITED
and
.Dv WTRAPPED
set in the
.Fa options
and with
.Fa infop
set to
.Dv NULL ,
is similar to
.Fn wait4 .
.Pp
The following macros may be used to test the manner of exit of the process.
One of the first four macros will evaluate to a non-zero (true) value:
@ -284,6 +510,7 @@ is returned and
is set to indicate the error.
.Pp
If
.Fn wait6 ,
.Fn wait4 ,
.Fn wait3 ,
or
@ -306,6 +533,18 @@ a value of -1
is returned and
.Va errno
is set to indicate the error.
.Pp
If
.Fn waitid
returns because one or more processes have a state change to report,
0 is returned.
To indicate an error, -1 will be returned and
.Dv errno
set to an appropriate value.
If
.Dv WNOHANG
was used, 0 can be returned indicating no error, but no processes
may have changed state either, if si_signo and/or si_pid are zero.
.Sh ERRORS
The
.Fn wait
@ -335,6 +574,14 @@ The call was interrupted by a caught signal,
or the signal did not have the
.Dv SA_RESTART
flag set.
.It Bq Er EINVAL
An invalid value was specified for
.Fa options ,
or
.Fa idtype
and
.Fa id
do not specify a valid set of processes.
.El
.Sh SEE ALSO
.Xr _exit 2 ,
@ -344,11 +591,13 @@ flag set.
.Xr siginfo 3
.Sh STANDARDS
The
.Fn wait
.Fn wait ,
.Fn waitpid ,
and
.Fn waitpid
.Fn waitid
functions are defined by POSIX;
.Fn wait4
.Fn wait6 ,
.Fn wait4 ,
and
.Fn wait3
are not specified by POSIX.