1SHMAT(P) POSIX Programmer's Manual SHMAT(P)
2
6 shmat - XSI shared memory attach operation
7
9 #include <sys/shm.h>
10 void *shmat(int shmid, const void *shmaddr, int shmflg);
12
15 The shmat() function operates on XSI shared memory (see the Base Defi‐
16 nitions volume of IEEE Std 1003.1-2001, Section 3.340, Shared Memory
17 Object). It is unspecified whether this function interoperates with the
18 realtime interprocess communication facilities defined in Realtime .
19 The shmat() function attaches the shared memory segment associated with
21 the shared memory identifier specified by shmid to the address space of
22 the calling process. The segment is attached at the address specified
23 by one of the following criteria:
24 * If shmaddr is a null pointer, the segment is attached at the first
26 available address as selected by the system.
27 * If shmaddr is not a null pointer and (shmflg &SHM_RND) is non-zero,
29 the segment is attached at the address given by (shmaddr
30 -((uintptr_t)shmaddr %SHMLBA)). The character '%' is the C-language
31 remainder operator.
32 * If shmaddr is not a null pointer and (shmflg &SHM_RND) is 0, the
34 segment is attached at the address given by shmaddr.
35 * The segment is attached for reading if (shmflg &SHM_RDONLY) is non-
37 zero and the calling process has read permission; otherwise, if it
38 is 0 and the calling process has read and write permission, the seg‐
39 ment is attached for reading and writing.
40
42 Upon successful completion, shmat() shall increment the value of
43 shm_nattch in the data structure associated with the shared memory ID
44 of the attached shared memory segment and return the segment's start
45 address.
46 Otherwise, the shared memory segment shall not be attached, shmat()
48 shall return -1, and errno shall be set to indicate the error.
49
51 The shmat() function shall fail if:
52 EACCES Operation permission is denied to the calling process; see XSI
54 Interprocess Communication .
55 EINVAL The value of shmid is not a valid shared memory identifier, the
57 shmaddr is not a null pointer, and the value of (shmaddr
58 -((uintptr_t)shmaddr %SHMLBA)) is an illegal address for attach‐
59 ing shared memory; or the shmaddr is not a null pointer, (shmflg
60 &SHM_RND) is 0, and the value of shmaddr is an illegal address
61 for attaching shared memory.
62 EMFILE The number of shared memory segments attached to the calling
64 process would exceed the system-imposed limit.
65 ENOMEM The available data space is not large enough to accommodate the
67 shared memory segment.
68 The following sections are informative.
71
73 None.
74
76 The POSIX Realtime Extension defines alternative interfaces for inter‐
77 process communication. Application developers who need to use IPC
78 should design their applications so that modules using the IPC routines
79 described in XSI Interprocess Communication can be easily modified to
80 use the alternative interfaces.
81
83 None.
84
86 None.
87
89 XSI Interprocess Communication , Realtime , exec() , exit() , fork() ,
90 shmctl() , shmdt() , shmget() , shm_open() , shm_unlink() , the Base
91 Definitions volume of IEEE Std 1003.1-2001, <sys/shm.h>
92
94 Portions of this text are reprinted and reproduced in electronic form
95 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
96 -- Portable Operating System Interface (POSIX), The Open Group Base
97 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
98 Electrical and Electronics Engineers, Inc and The Open Group. In the
99 event of any discrepancy between this version and the original IEEE and
100 The Open Group Standard, the original IEEE and The Open Group Standard
101 is the referee document. The original Standard can be obtained online
102 at http://www.opengroup.org/unix/online.html .
103IEEE/The Open Group 2003 SHMAT(P)