1.\"
2.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
3.\"
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26.\" $FreeBSD: head/lib/libc/sys/semctl.2 108087 2002-12-19 09:40:28Z ru $
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| 26.\" $FreeBSD: head/lib/libc/sys/semctl.2 131504 2004-07-02 23:52:20Z ru $ |
27.\"
28.Dd September 12, 1995
29.Dt SEMCTL 2
30.Os
31.Sh NAME
32.Nm semctl
33.Nd control operations on a semaphore set
34.Sh LIBRARY
35.Lb libc
36.Sh SYNOPSIS
37.In sys/types.h
38.In sys/ipc.h
39.In sys/sem.h
40.Ft int
41.Fn semctl "int semid" "int semnum" "int cmd" ...
42.Sh DESCRIPTION
43The
44.Fn semctl
45system call
46performs the operation indicated by
47.Fa cmd
48on the semaphore set indicated by
49.Fa semid .
50A fourth argument, a
51.Fa "union semun arg" ,
52is required for certain values of
53.Fa cmd .
54For the commands that use the
55.Fa arg
56argument,
57.Fa "union semun"
58is defined as follows:
59.Bd -literal
60.\"
61.\" From <sys/sem.h>:
62.\"
63union semun {
64 int val; /* value for SETVAL */
65 struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */
66 u_short *array; /* array for GETALL & SETALL */
67};
68.Ed
69.Pp
70Commands are performed as follows:
71.\"
72.\" This section based on Stevens, _Advanced Programming in the UNIX
73.\" Environment_.
74.\"
75.Bl -tag -width IPC_RMIDXXX
76.It Dv IPC_STAT
77Fetch the semaphore set's
78.Fa "struct semid_ds" ,
79storing it in the memory pointed to by
80.Fa arg.buf .
81.It Dv IPC_SET
82Changes the
83.Fa sem_perm.uid ,
84.Fa sem_perm.gid ,
85and
86.Fa sem_perm.mode
87members of the semaphore set's
88.Fa "struct semid_ds"
89to match those of the struct pointed to by
90.Fa arg.buf .
91The calling process's effective uid must
92match either
93.Fa sem_perm.uid
94or
95.Fa sem_perm.cuid ,
96or it must have superuser privileges.
97.It IPC_RMID
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98Immediately removes the semaphore set from the system. The calling
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98Immediately removes the semaphore set from the system.
99The calling |
100process's effective uid must equal the semaphore set's
101.Fa sem_perm.uid
102or
103.Fa sem_perm.cuid ,
104or the process must have superuser privileges.
105.It Dv GETVAL
106Return the value of semaphore number
107.Fa semnum .
108.It Dv SETVAL
109Set the value of semaphore number
110.Fa semnum
111to
112.Fa arg.val .
113Outstanding adjust on exit values for this semaphore in any process
114are cleared.
115.It Dv GETPID
116Return the pid of the last process to perform an operation on
117semaphore number
118.Fa semnum .
119.It Dv GETNCNT
120Return the number of processes waiting for semaphore number
121.Fa semnum Ns 's
122value to become greater than its current value.
123.It Dv GETZCNT
124Return the number of processes waiting for semaphore number
125.Fa semnum Ns 's
126value to become 0.
127.It Dv GETALL
128Fetch the value of all of the semaphores in the set into the
129array pointed to by
130.Fa arg.array .
131.It Dv SETALL
132Set the values of all of the semaphores in the set to the values
133in the array pointed to by
134.Fa arg.array .
135Outstanding adjust on exit values for all semaphores in this set,
136in any process are cleared.
137.El
138.Pp
139The
140.Vt "struct semid_ds"
141is defined as follows:
142.Bd -literal
143.\"
144.\" Taken straight from <sys/sem.h>.
145.\"
146struct semid_ds {
147 struct ipc_perm sem_perm; /* operation permission struct */
148 struct sem *sem_base; /* pointer to first semaphore in set */
149 u_short sem_nsems; /* number of sems in set */
150 time_t sem_otime; /* last operation time */
151 long sem_pad1; /* SVABI/386 says I need this here */
152 time_t sem_ctime; /* last change time */
153 /* Times measured in secs since */
154 /* 00:00:00 GMT, Jan. 1, 1970 */
155 long sem_pad2; /* SVABI/386 says I need this here */
156 long sem_pad3[4]; /* SVABI/386 says I need this here */
157};
158.Ed
159.Sh RETURN VALUES
160On success, when
161.Fa cmd
162is one of
163.Dv GETVAL , GETPID , GETNCNT
164or
165.Dv GETZCNT ,
166.Fn semctl
167returns the corresponding value; otherwise, 0 is returned.
168On failure, -1 is returned, and
169.Va errno
170is set to indicate the error.
171.Sh ERRORS
172The
173.Fn semctl
174system call
175will fail if:
176.Bl -tag -width Er
177.It Bq Er EINVAL
178No semaphore set corresponds to
179.Fa semid .
180.It Bq Er EINVAL
181The
182.Fa semnum
183argument
184is not in the range of valid semaphores for given semaphore set.
185.It Bq Er EPERM
186The calling process's effective uid does not match the uid of
187the semaphore set's owner or creator.
188.It Bq Er EACCES
189Permission denied due to mismatch between operation and mode of
190semaphore set.
191.It Bq Er ERANGE
192.Dv SETVAL
193or
194.Dv SETALL
195attempted to set a semaphore outside the allowable range
196.Bq 0 .. Dv SEMVMX .
197.El
198.Sh SEE ALSO
199.Xr semget 2 ,
200.Xr semop 2
201.Sh BUGS
202.Dv SETALL
203may update some semaphore elements before returning an error.
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