bsd/man/man2/shmat.2

   1 .\"   $OpenBSD: shmat.2,v 1.2 1996/10/08 01:20:15 michaels Exp $
   2 .\"     $NetBSD: shmat.2,v 1.1 1995/10/16 23:49:29 jtc Exp $
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   4 .\" Copyright (c) 1995 Frank van der Linden
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  33 .Dd August 17, 1995
  34 .Dt SHMAT 2
  35 .Os
  36 .Sh NAME
  37 .Nm shmat ,
  38 .Nm shmdt
  39 .Nd map/unmap shared memory
  40 .Sh SYNOPSIS
  41 .Fd #include <sys/types.h>
  42 .Fd #include <sys/ipc.h>
  43 .Fd #include <sys/shm.h>
  44 .Ft void *
  45 .Fn shmat "int shmid" "void *shmaddr" "int shmflg"
  46 .Ft int
  47 .Fn shmdt "void *shmaddr"
  48 .Sh DESCRIPTION
  49 .Fn shmat
  50 maps the shared memory segment associated with the shared memory identifier
  51 .Fa shmid
  52 into the address space of the calling process. The address at which the
  53 segment is mapped is determined by the
  54 .Fa shmaddr
  55 parameter. If it is equal to 0, the system will pick an address itself.
  56 Otherwise, an attempt is made to map the shared memory segment at the
  57 address
  58 .Fa shmaddr
  59 specifies. If SHM_RND is set in
  60 .Fa shmflg ,
  61 the system will round the address down to a multiple of SHMLBA bytes
  62 (SHMLBA is defined in
  63 .Aq Pa sys/shm.h
  64 ).
  65
  66 A shared memory segment can be mapped read-only by specifying the
  67 SHM_RDONLY flag in
  68 .Fa shmflg .
  69
  70 .Fn shmdt
  71 unmaps the shared memory segment that is currently mapped at
  72 .Fa shmaddr
  73 from the calling process' address space.
  74 .Fa shmaddr
  75 must be a value returned by a prior
  76 .Fn shmat
  77 call. A shared memory segment will remain existant until it is removed by
  78 a call to
  79 .Xr shmctl 2
  80 with the IPC_RMID command.
  81 .Sh RETURN VALUES
  82 .Fn shmat
  83 returns the address at which the shared memory segment has been mapped into
  84 the calling process' address space when successful,
  85 .Fn shmdt
  86 returns 0 on successful completion. Otherwise, a value of -1 is returned,
  87 and the global variable
  88 .Va errno
  89 is set to indicate the error.
  90 .Sh ERRORS
  91 .Fn shmat
  92 will fail if:
  93 .Bl -tag -width Er
  94 .It Bq Er EACCESS
  95 The calling process has no permission to access this shared memory segment.
  96 .It Bq Er ENOMEM
  97 There is not enough available data space for the calling process to
  98 map the shared memory segment.
  99 .It Bq Er EINVAL
 100 .Fa shmid
 101 is not a valid shared memory identifier.
 102
 103 .Fa shmaddr
 104 specifies an illegal address.
 105 .It Bq Er EMFILE
 106 The number of shared memory segments has reached the system-wide limit.
 107 .El
 108
 109 .Fn shmdt
 110 will fail if:
 111 .Bl -tag -width Er
 112 .It Bq Er EINVAL
 113 .Fa shmaddr
 114 is not the start address of a mapped shared memory segment.
 115 .Sh SEE ALSO
 116 .Xr shmctl 2 ,
 117 .Xr shmget 2 ,
 118 .Xr mmap 2