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