#include <machine/param.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h> int
shmget (key_t key size_t size int flag);
DESCRIPTION
Based on the values of
Fa key
and
Fa flag ,
shmget ();
returns the identifier of a newly created or previously existing shared
memory segment.
The key
is analogous to a filename: it provides a handle that names an
IPC object.
There are three ways to specify a key:
IPC_PRIVATE may be specified, in which case a new IPC object
will be created.
An integer constant may be specified.
If no IPC object corresponding
to
Fa key
is specified and the IPC_CREAT bit is set in
Fa flag ,
a new one will be created.
The
ftok(3)
may be used to generate a key from a pathname.
The mode of a newly created IPC object is determined by
OR 'ing
the following constants into the
Fa flag
argument:
SHM_R
Read access for user.
SHM_W
Write access for user.
( SHM_R>>3
Read access for group.
( SHM_W>>3
Write access for group.
( SHM_R>>6
Read access for other.
( SHM_W>>6
Write access for other.
When creating a new shared memory segment,
Fa size
indicates the desired size of the new segment in bytes.
The size
of the segment may be rounded up to a multiple convenient to the
kernel (i.e., the page size).
RETURN VALUES
Upon successful completion,
shmget ();
returns the positive integer identifier of a shared memory segment.
Otherwise, -1 is returned and
errno
set to indicate the error.
ERRORS
The
shmget ();
system call
will fail if:
Bq Er EINVAL
Size specified is greater than the size of the previously existing segment.
Size specified is less than the system imposed minimum, or greater than
the system imposed maximum.
Bq Er ENOENT
No shared memory segment was found matching
Fa key ,
and IPC_CREAT was not specified.
Bq Er ENOSPC
The kernel was unable to allocate enough memory to
satisfy the request.
Bq Er EEXIST
IPC_CREAT and IPC_EXCL were specified, and a shared memory segment
corresponding to
Fa key
already exists.
