shmop(2)shmop(2)Name
shmop, shmat, shmdt - shared memory operations
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
char *shmat (shmid, shmaddr, shmflg)
int shmid;
char *shmaddr;
int shmflg;
int shmdt (shmaddr)
char *shmaddr;
Description
The system call attaches the shared memory segment associated with the
shared memory identifier specified by shmid to the data segment of the
calling process. The segment is attached at the address specified by
one of the following criteria:
If shmaddr is equal to zero, the segment is attached at the first
available address as selected by the system.
If shmaddr is not equal to zero and (shmflg & SHM_RND ) is true, the
segment is attached at the address given by (shmaddr- (shmaddr modulus
SHMLBA )).
If shmaddr is not equal to zero and (shmflg & SHM_RND ) is false, the
segment is attached at the address given by shmaddr.
The segment is attached for reading if (shmflg & SHM_RDONLY ) is true.
Otherwise, it is attached for reading and writing.
The system call detaches from the calling process's data segment the
shared memory segment located at the address specified by shmaddr.
Return Values
Upon successful completion, the return values are as follows:
· The system call returns the data segment start address of the
attached shared memory segment.
· The system call returns a value of zero (0).
Otherwise, a value of -1 is returned, and errno is set to indicate the
error.
Diagnostics
The system call fails and not attach the shared memory segment, if any
of the following is true:
[EINVAL] The shmid is not a valid shared memory identifier.
[EACCES] Operation permission is denied to the calling process.
For further information, see
[ENOMEM] The available data space is not large enough to accommo‐
date the shared memory segment.
[EINVAL] The shmaddr is not equal to zero, and the value of
(shmaddr- (shmaddr modulus SHMLBA )) is an illegal
address.
[EINVAL] The shmaddr is not equal to zero, (shmflg & SHM_RND ) is
false, and the value of shmaddr is an illegal address.
[EMFILE] The number of shared memory segments attached to the
calling process would exceed the system imposed limit.
The fails and does not detach the shared memory segment if:
[EINVAL] The shmaddr is not the data segment start address of a
shared memory segment.
See Alsoexecve(2), exit(2), fork(2), shmctl(2), shmget(2)shmop(2)
