1.\" $NetBSD: shmat.2,v 1.14 2002/10/01 18:10:45 wiz Exp $ 2.\" 3.\" Copyright (c) 1995 Frank van der Linden 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project 17.\" by Frank van der Linden 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.Dd June 17, 2002 33.Dt SHMAT 2 34.Os 35.Sh NAME 36.Nm shmat , 37.Nm shmdt 38.Nd map/unmap shared memory 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.Fd #include \*[Lt]sys/shm.h\*[Gt] 43.Ft void * 44.Fn shmat "int shmid" "const void *shmaddr" "int shmflg" 45.Ft int 46.Fn shmdt "const void *shmaddr" 47.Sh DESCRIPTION 48.Fn shmat 49maps the shared memory segment associated with the shared memory identifier 50.Fa shmid 51into the address space of the calling process. 52The address at which the segment is mapped is determined by the 53.Fa shmaddr 54parameter. 55If it is equal to 0, the system will pick an address itself. 56Otherwise, an attempt is made to map the shared memory segment at the 57address 58.Fa shmaddr 59specifies. 60If 61.Dv SHM_RND 62is set in 63.Fa shmflg , 64the system will round the address down to a multiple of 65.Dv SHMLBA 66bytes 67.Pf ( Dv SHMLBA 68is defined in 69.Aq Pa sys/shm.h ) . 70.Pp 71A shared memory segment can be mapped read-only by specifying the 72.Dv SHM_RDONLY 73flag in 74.Fa shmflg . 75.Pp 76.Fn shmdt 77unmaps the shared memory segment that is currently mapped at 78.Fa shmaddr 79from the calling process' address space. 80.Fa shmaddr 81must be a value returned by a prior 82.Fn shmat 83call. 84A shared memory segment will remain in existence until it is 85removed by a call to 86.Xr shmctl 2 87with the 88.Dv IPC_RMID 89command. 90.Sh RETURN VALUES 91.Fn shmat 92returns the address at which the shared memory segment has been mapped into 93the calling process' address space when successful, 94.Fn shmdt 95returns 0 on successful completion. 96Otherwise, a value of -1 is returned, and the global variable 97.Va errno 98is set to indicate the error. 99.Sh ERRORS 100.Fn shmat 101will fail if: 102.Bl -tag -width Er 103.It Bq Er EACCES 104The calling process has no permission to access this shared memory segment. 105.It Bq Er ENOMEM 106There is not enough available data space for the calling process to 107map the shared memory segment. 108.It Bq Er EINVAL 109.Fa shmid 110is not a valid shared memory identifier. 111.Pp 112.Fa shmaddr 113specifies an illegal address. 114.It Bq Er EMFILE 115The number of shared memory segments has reached the system-wide limit. 116.El 117.Pp 118.Fn shmdt 119will fail if: 120.Bl -tag -width Er 121.It Bq Er EINVAL 122.Fa shmaddr 123is not the start address of a mapped shared memory segment. 124.El 125.Sh SEE ALSO 126.Xr ipcrm 1 , 127.Xr ipcs 1 , 128.Xr mmap 2 , 129.Xr shmctl 2 , 130.Xr shmget 2 131.Sh STANDARDS 132The 133.Nm shmat 134and 135.Nm shmdt 136system calls conform to 137.St -xsh5 . 138.Sh HISTORY 139Shared memory segments appeared in the first release of 140.At V . 141