SHMOP(2)

NAME
shmop, shmat, shmdt - shared memory operations

SYNOPSIS
#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
Shmat 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 % 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'' and the calling process has read permission, otherwise it is attached for reading and writing provided the caller has read and write permissions (see kedef(2)).

Shmdt 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 value is as follows:

    Shmat returns the data segment start address of the attached shared memory segment.

    Shmdt returns a value of 0.

Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

Shmat will fail and not attach the shared memory segment if one or more of the following are true:

EINVAL
    Shmid is not a valid shared memory identifier.

EACCES
    Operation permission is denied to the calling process (see kedef(2)).

ENOMEM
    The available data space is not large enough to accommodate the shared memory segment.

EINVAL
    Shmaddr is not equal to zero, and the value of (shmaddr - (shmaddr % SHMLBA)) is an illegal address.

EINVAL
    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.

Shmdt will fail and not detach the shared memory segment if:

EINVAL
    shmaddr is not the data segment start address of a shared memory segment.

SEE ALSO
exec(2), exit(2), fork(2), kedef(2), shmctl(2), shmget(2).