NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SUMMARY OF TRUSTED SOLARIS CHANGES | SEE ALSO
#include <sys/types.h> #include <sys/shm.h>void *shmat(int shmid, const void *shmaddr, int shmflg);
The shmat() function attaches the shared memory segment associated with the shared memory identifier specified by shmid to the data segment of the calling process.
The permission required for a shared memory control operation is given as {token}, where token is the type of permission needed. The types of permission are interpreted as follows:
00400 READ by user 00200 WRITE by user 00040 READ by group 00020 WRITE by group 00004 READ by others 00002 WRITE by others
See the Shared Memory Operation Permissions section of intro(2) for more information.
A process attempting to map a shared-memory
segment as read-only (shmflg&SHM_RDONLY) must either have discretionary and mandatory read access to the shared-memory object or have the necessary privileges in its set of effective privileges: PRIV_IPC_DAC_READ
and PRIV_IPC_MAC_READ
. Otherwise, mapping the shared-memory segment for reading and writing requires that the process have discretionary and mandatory read access and discretionary and mandatory write access to the shared memory object, or that the effective privilege set of
the process include these privileges as necessary: PRIV_IPC_DAC_READ
, PRIV_IPC_MAC_READ
, PRIV_IPC_DAC_WRITE
, and PRIV_IPC_MAC_WRITE
.
When (shmflg&SHM_SHARE_MMU) is true, virtual memory resources in addition to shared memory itself are shared among processes that use the same shared memory.
The shared memory segment is attached to the data segment of the calling process at the address specified based on one of the following criteria:
If shmaddr is equal to (void *) 0, the segment is attached to the first available address as selected by the system.
If shmaddr is equal to (void *) 0 and (shmflg&SHM_SHARE_MMU) is true, then the segment is attached to the first available suitably aligned address. When (shmflg&SHM_SHARE_MMU) is set, however, the permission given by shmget() determines whether the segment is attached for reading or reading and writing.
If shmaddr is not equal to (void *) 0 and (shmflg&SHM_RND) is true, the segment is attached to the address given by (shmaddr - (shmaddr modulus SHMLBA)).
If shmaddr is not equal to (void *) 0 and (shmflg&SHM_RND) is false, the segment is attached to the address given by shmaddr.
The segment is attached for reading if (shmflg&SHM_RDONLY) is true {READ}, otherwise it is attached for reading and writing {READ/WRITE}.
The shmdt() function detaches from the calling process's data segment the shared memory segment located at the address specified by shmaddr. If the application is standard-conforming [see standards(5)], the shmaddr argument is of type const void *. Otherwise it is of type char *.
Shared memory segments must be explicitly removed after the last reference to them has been removed.
Upon successful completion, shmat() returns the data segment start address of the attached shared memory segment; shmdt() returns 0. Otherwise, -1 is returned, the shared memory segment is not attached, and errno is set to indicate the error.
The shmat() function will fail if:
Operation permission is denied to the calling process [see intro(2)], and the calling process does not have the appropriate privilege(s) in its set of effective privileges.
The shmid argument is not a valid shared memory identifier.
The shmaddr argument is not equal to 0, and the value of (shmaddr - (shmaddr modulus SHMLBA)) is an illegal address.
The shmaddr argument is not equal to 0, is an illegal address, and (shmflg&SHM_RND) is false.
The shmaddr argument is not equal to 0, is not properly aligned, and (shmfg&SHM_SHARE_MMU) is true.
SHM_SHARE_MMU is not supported in certain architectures.
The number of shared memory segments attached to the calling process would exceed the system-imposed limit.
The available data space is not large enough to accommodate the shared memory segment.
The LOCK and UNLOCK operation does not have the appropriate privilege in its set of effective privileges.
The shmdt() function will fail if:
The shmaddr argument is not the data segment start address of a shared memory segment.
Appropriate privilege is required to override access checks.
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SUMMARY OF TRUSTED SOLARIS CHANGES | SEE ALSO