bsd/man/man2/semctl.2

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   2 .\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>
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  26 .\" $FreeBSD: src/lib/libc/sys/semctl.2,v 1.18 2002/12/19 09:40:25 ru Exp $
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  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
  43 The
  44 .Fn semctl
  45 system call
  46 performs the operation indicated by
  47 .Fa cmd
  48 on the semaphore set indicated by
  49 .Fa semid .
  50 A fourth argument, a
  51 .Fa "union semun arg" ,
  52 is required for certain values of
  53 .Fa cmd .
  54 For the commands that use the
  55 .Fa arg
  56 argument,
  57 .Fa "union semun"
  58 is defined as follows:
  59 .Bd -literal
  60 .\"
  61 .\" From <sys/sem.h>:
  62 .\"
  63 union 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
  70 Commands 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
  77 Fetch the semaphore set's
  78 .Fa "struct semid_ds" ,
  79 storing it in the memory pointed to by
  80 .Fa arg.buf .
  81 .It Dv IPC_SET
  82 Changes the
  83 .Fa sem_perm.uid ,
  84 .Fa sem_perm.gid ,
  85 and
  86 .Fa sem_perm.mode
  87 members of the semaphore set's
  88 .Fa "struct semid_ds"
  89 to match those of the struct pointed to by
  90 .Fa arg.buf .
  91 The calling process's effective uid must
  92 match either
  93 .Fa sem_perm.uid
  94 or
  95 .Fa sem_perm.cuid ,
  96 or it must have superuser privileges.
  97 .It IPC_RMID
  98 Immediately removes the semaphore set from the system.  The calling
  99 process's effective uid must equal the semaphore set's
 100 .Fa sem_perm.uid
 101 or
 102 .Fa sem_perm.cuid ,
 103 or the process must have superuser privileges.
 104 .It Dv GETVAL
 105 Return the value of semaphore number
 106 .Fa semnum .
 107 .It Dv SETVAL
 108 Set the value of semaphore number
 109 .Fa semnum
 110 to
 111 .Fa arg.val .
 112 Outstanding adjust on exit values for this semaphore in any process
 113 are cleared.
 114 .It Dv GETPID
 115 Return the pid of the last process to perform an operation on
 116 semaphore number
 117 .Fa semnum .
 118 .It Dv GETNCNT
 119 Return the number of processes waiting for semaphore number
 120 .Fa semnum Ns 's
 121 value to become greater than its current value.
 122 .It Dv GETZCNT
 123 Return the number of processes waiting for semaphore number
 124 .Fa semnum Ns 's
 125 value to become 0.
 126 .It Dv GETALL
 127 Fetch the value of all of the semaphores in the set into the
 128 array pointed to by
 129 .Fa arg.array .
 130 .It Dv SETALL
 131 Set the values of all of the semaphores in the set to the values
 132 in the array pointed to by
 133 .Fa arg.array .
 134 Outstanding adjust on exit values for all semaphores in this set,
 135 in any process are cleared.
 136 .El
 137 .Pp
 138 The
 139 .Vt "struct semid_ds"
 140 is defined as follows:
 141 .Bd -literal
 142 .\"
 143 .\" Taken straight from <sys/sem.h>.
 144 .\"
 145 struct semid_ds {
 146         struct  ipc_perm sem_perm;      /* operation permission struct */
 147         struct  sem *sem_base;  /* pointer to first semaphore in set */
 148         u_short sem_nsems;      /* number of sems in set */
 149         time_t  sem_otime;      /* last operation time */
 150         long    sem_pad1;       /* SVABI/386 says I need this here */
 151         time_t  sem_ctime;      /* last change time */
 152                                 /* Times measured in secs since */
 153                                 /* 00:00:00 GMT, Jan. 1, 1970 */
 154         long    sem_pad2;       /* SVABI/386 says I need this here */
 155         long    sem_pad3[4];    /* SVABI/386 says I need this here */
 156 };
 157 .Ed
 158 .Sh RETURN VALUES
 159 On success, when
 160 .Fa cmd
 161 is one of
 162 .Dv GETVAL , GETPID , GETNCNT
 163 or
 164 .Dv GETZCNT ,
 165 .Fn semctl
 166 returns the corresponding value; otherwise, 0 is returned.
 167 On failure, -1 is returned, and
 168 .Va errno
 169 is set to indicate the error.
 170 .Sh ERRORS
 171 The
 172 .Fn semctl
 173 system call
 174 will fail if:
 175 .Bl -tag -width Er
 176 .It Bq Er EINVAL
 177 No semaphore set corresponds to
 178 .Fa semid .
 179 .It Bq Er EINVAL
 180 The
 181 .Fa semnum
 182 argument
 183 is not in the range of valid semaphores for given semaphore set.
 184 .It Bq Er EPERM
 185 The calling process's effective uid does not match the uid of
 186 the semaphore set's owner or creator.
 187 .It Bq Er EACCES
 188 Permission denied due to mismatch between operation and mode of
 189 semaphore set.
 190 .It Bq Er ERANGE
 191 .Dv SETVAL
 192 or
 193 .Dv SETALL
 194 attempted to set a semaphore outside the allowable range
 195 .Bq 0 .. Dv SEMVMX .
 196 .El
 197 .Sh SEE ALSO
 198 .Xr semget 2 ,
 199 .Xr semop 2
 200 .Sh BUGS
 201 .Dv SETALL
 202 may update some semaphore elements before returning an error.