SHMOP(2) SHMOP(2)
NAME
shmop - 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 & SHMRND)
is ``true'', the segment is attached at the address
given by (shmaddr - (shmaddr modulus SHMLBA)).
If shmaddr is not equal to zero and (shmflg & SHMRND)
is ``false'', the segment is attached at the address
given by shmaddr.
Shmdt detaches from the calling process's data segment the
shared memory segment located at the address specified by
shmaddr.
The segment is attached for reading if (shmflg & SHMRDONLY)
is ``true'' {READ}, otherwise it is attached for reading and
writing {READ/WRITE}.
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SHMOP(2) SHMOP(2)
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 intro(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 modulus SHMLBA)) is an
illegal address.
[EINVAL] Shmaddr is not equal to zero, (shmflg &
SHMRND) 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.
[EINVAL] Shmdt will fail and not detach the shared
memory segment if shmaddr is not the data
segment start address of a shared memory
segment.
SEE ALSO
exec(2), exit(2), fork(2), intro(2), shmctl(2), shmget(2).
DIAGNOSTICS
Upon successful completion, the return value is as follows:
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SHMOP(2) SHMOP(2)
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.
NOTES
The user must explicitly remove shared memory segments after
the last reference to them has been removed.
Page 3 May 1989