bsd/man/man2/shmctl.2

   1 .\"   $OpenBSD: shmctl.2,v 1.2 1996/10/08 01:20:15 michaels Exp $
   2 .\"     $NetBSD: shmctl.2,v 1.1 1995/10/16 23:49:30 jtc Exp $
   3 .\"
   4 .\" Copyright (c) 1995 Frank van der Linden
   5 .\" All rights reserved.
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  17 .\"      This product includes software developed for the NetBSD Project
  18 .\"      by Frank van der Linden
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  33 .Dd August 17, 1995
  34 .Dt SHMCTL 2
  35 .Os
  36 .Sh NAME
  37 .Nm shmctl
  38 .Nd shared memory control operations
  39 .Sh SYNOPSIS
  40 .Fd #include <sys/shm.h>
  41 .Ft int
  42 .Fo shmctl
  43 .Fa "int shmid"
  44 .Fa "int cmd"
  45 .Fa "struct shmid_ds *buf"
  46 .Fc
  47 .Sh DESCRIPTION
  48 The
  49 .Fn shmctl
  50 system call performs some control operations on the shared memory area
  51 specified by
  52 .Fa shmid .
  53 Each shared memory segment has a data structure associated with it,
  54 parts of which may be altered by
  55 .Fn shmctl
  56 and parts of which determine the actions of
  57 .Fn shmctl .
  58 This structure is defined as follows in
  59 .Aq Pa sys/shm.h :
  60 .Bd -literal
  61 struct shmid_ds {
  62     struct ipc_perm  shm_perm;     /* operation permissions */
  63     int              shm_segsz;    /* size of segment in bytes */
  64     pid_t            shm_lpid;     /* pid of last shm op */
  65     pid_t            shm_cpid;     /* pid of creator */
  66     short            shm_nattch;   /* # of current attaches */
  67     time_t           shm_atime;    /* last shmat() time*/
  68     time_t           shm_dtime;    /* last shmdt() time */
  69     time_t           shm_ctime;    /* last change by shmctl() */
  70     void            *shm_internal; /* sysv stupidity */
  71 };
  72 .Ed
  73 .Pp
  74 The
  75 .Bf -literal
  76 ipc_perm
  77 .Ef
  78 structure used inside the
  79 .Bf -literal
  80 shmid_ds
  81 .Ef
  82 structure is defined in
  83 .Aq Pa sys/ipc.h
  84 and looks like this:
  85 .Bd -literal
  86 struct ipc_perm {
  87   uid_t           uid;   /* Owner's user ID */
  88   gid_t           gid;   /* Owner's group ID */
  89   uid_t           cuid;  /* Creator's user ID */
  90   gid_t           cgid;  /* Creator's group ID */
  91   mode_t          mode;  /* r/w permission (see chmod(2)) */
  92   unsigned short  _seq;  /* Reserved for internal use */
  93   key_t           _key;  /* Reserved for internal use */
  94 };
  95 .Ed
  96 .Pp
  97 The operation to be performed by
  98 .Fn shmctl
  99 is specified in
 100 .Fa cmd
 101 and is one of:
 102 .Bl -tag -width IPC_RMIDX
 103 .It Dv IPC_STAT
 104 Gather information about the shared memory segment and place it in the
 105 structure pointed to by
 106 .Fa buf .
 107 .It Dv IPC_SET
 108 Set the value of the
 109 .Va shm_perm.uid ,
 110 .Va shm_perm.gid
 111 and
 112 .Va shm_perm.mode
 113 fields in the structure associated with
 114 .Fa shmid .
 115 The values are taken from the corresponding fields in the structure
 116 pointed to by
 117 .Fa buf .
 118 This operation can only be executed by the super-user, or a process that
 119 has an effective user id equal to either
 120 .Va shm_perm.cuid
 121 or
 122 .Va shm_perm.uid
 123 in the data structure associated with the shared memory segment.
 124 .It Dv IPC_RMID
 125 Remove the shared memory segment specified by
 126 .Fa shmid
 127 and destroy the data associated with it. Only the super-user or a process
 128 with an effective uid equal to the
 129 .Va shm_perm.cuid
 130 or
 131 .Va shm_perm.uid
 132 values in the data structure associated with the queue can do this.
 133 .El
 134 .Pp
 135 The read and write permissions on a shared memory identifier
 136 are determined by the
 137 .Va shm_perm.mode
 138 field in the same way as is
 139 done with files (see
 140 .Xr chmod 2 ),
 141 but the effective uid can match either the
 142 .Va shm_perm.cuid
 143 field or the
 144 .Va shm_perm.uid
 145 field, and the
 146 effective gid can match either
 147 .Va shm_perm.cgid
 148 or
 149 .Va shm_perm.gid .
 150 .Sh RETURN VALUES
 151 Upon successful completion, a value of 0 is returned.
 152 Otherwise, -1 is returned and the global variable
 153 .Va errno
 154 is set to indicate the error.
 155 .Sh ERRORS
 156 .Fn shmctl
 157 will fail if:
 158 .Bl -tag -width Er
 159 .\" ===========
 160 .It Bq Er EACCES
 161 The command is IPC_STAT
 162 and the caller has no read permission for this shared memory segment.
 163 .\" ===========
 164 .It Bq Er EFAULT
 165 .Fa buf
 166 specifies an invalid address.
 167 .\" ===========
 168 .It Bq Er EINVAL
 169 .Fa shmid
 170 is not a valid shared memory segment identifier.
 171 .Va cmd
 172 is not a valid command.
 173 .\" ===========
 174 .It Bq Er EPERM
 175 .Fa cmd
 176 is equal to IPC_SET or IPC_RMID and the caller is not the super-user,\
 177 nor does the effective uid match either the
 178 .Va shm_perm.uid
 179 or
 180 .Va shm_perm.cuid
 181 fields of the data structure associated with the shared memory segment.
 182 An attempt is made to increase the value of
 183 .Va shm_qbytes
 184 through IPC_SET
 185 but the caller is not the super-user.
 186 .El
 187 .Sh LEGACY SYNOPSIS
 188 .Fd #include <sys/types.h>
 189 .Fd #include <sys/ipc.h>
 190 .Fd #include <sys/shm.h>
 191 .Pp
 192 All of these include files are necessary.
 193 .Sh LEGACY DESCRIPTION
 194 The
 195 .Bf -literal
 196 ipc_perm
 197 .Ef
 198 structure used inside the
 199 .Bf -literal
 200 shmid_ds
 201 .Ef
 202 structure, as defined in
 203 .Aq Pa sys/ipc.h ,
 204 looks like this:
 205 .Bd -literal
 206 struct ipc_perm {
 207     __uint16_t cuid;  /* Creator's user id */
 208     __uint16_t cgid;  /* Creator's group id */
 209     __uint16_t uid;   /* Owner's user id */
 210     __uint16_t gid;   /* Owner's group id */
 211     mode_t     mode;  /* r/w permission (see chmod(2)) */
 212     __uint16_t seq;   /* Reserved for internal use */
 213     key_t      key;   /* Reserved for internal use */
 214 };
 215 .Ed
 216 .Pp
 217 This structure is maintained for binary backward compatibility
 218 with previous versions of the interface.
 219 New code should not use this interface,
 220 because ID values may be truncated.
 221 .Pp
 222 Specifically,
 223 LEGACY mode limits the allowable uid/gid ranges to 0-32767.
 224 If the user has a UID that is out of this range (e.g., "nobody"),
 225 software using the LEGACY API will not behave as expected.
 226 .Sh SEE ALSO
 227 .Xr shmat 2 ,
 228 .Xr shmdt 2 ,
 229 .Xr shmget 2 ,
 230 .Xr compat 5