Originální popis anglicky:
shmat - XSI shared memory attach operation
Návod, kniha: POSIX Programmer's Manual
#include <sys/shm.h>
void *shmat(int
shmid, const void
*shmaddr , int
shmflg );
The
shmat() function operates on XSI shared memory (see the Base
Definitions volume of IEEE Std 1003.1-2001, Section 3.340,
Shared Memory Object). It is unspecified whether this function interoperates
with the realtime interprocess communication facilities defined in
Realtime .
The
shmat() function attaches the shared memory segment associated with
the shared memory identifier specified by
shmid to the address space of
the calling process. The segment is attached at the address specified by one
of the following criteria:
- *
- If shmaddr is a null pointer, the segment is
attached at the first available address as selected by the system.
- *
- If shmaddr is not a null pointer and (shmflg
&SHM_RND) is non-zero, the segment is attached at the address given by
( shmaddr -((uintptr_t)shmaddr %SHMLBA)). The
character '%' is the C-language remainder operator.
- *
- If shmaddr is not a null pointer and (shmflg
&SHM_RND) is 0, the segment is attached at the address given by
shmaddr.
- *
- The segment is attached for reading if (shmflg
&SHM_RDONLY) is non-zero and the calling process has read permission;
otherwise, if it is 0 and the calling process has read and write
permission, the segment is attached for reading and writing.
Upon successful completion,
shmat() shall increment the value of
shm_nattch in the data structure associated with the shared memory ID
of the attached shared memory segment and return the segment's start address.
Otherwise, the shared memory segment shall not be attached,
shmat() shall
return -1, and
errno shall be set to indicate the error.
The
shmat() function shall fail if:
- EACCES
- Operation permission is denied to the calling process; see
XSI Interprocess Communication .
- EINVAL
- The value of shmid is not a valid shared memory
identifier, the shmaddr is not a null pointer, and the value of (
shmaddr -((uintptr_t)shmaddr %SHMLBA)) is an illegal
address for attaching shared memory; or the shmaddr is not a null
pointer, ( shmflg &SHM_RND) is 0, and the value of
shmaddr is an illegal address for attaching shared memory.
- EMFILE
- The number of shared memory segments attached to the
calling process would exceed the system-imposed limit.
- ENOMEM
- The available data space is not large enough to accommodate
the shared memory segment.
The following sections are informative.
None.
The POSIX Realtime Extension defines alternative interfaces for interprocess
communication. Application developers who need to use IPC should design their
applications so that modules using the IPC routines described in
XSI
Interprocess Communication can be easily modified to use the alternative
interfaces.
None.
None.
XSI Interprocess Communication ,
Realtime ,
exec() ,
exit() ,
fork() ,
shmctl() ,
shmdt() ,
shmget() ,
shm_open() ,
shm_unlink() , the Base
Definitions volume of IEEE Std 1003.1-2001,
<sys/shm.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
