shm_open.2 (2010 09)

s
shm_open(2) shm_open(2)
NAME
shm_open - create/open a shared memory object
SYNOPSIS
#include <sys/mman.h>
int shm_open(const char *name, int oflag, mode_t mode);
DESCRIPTION
The shm_open() system call establishes a connection between a shared memory object and a file
descriptor. It creates an open file description that corresponds to the shared memory object and returns a
file descriptor that refers to that open file description. This file descriptor (which is the lowest numbered
file descriptor not currently open for that process) is used by other functions to refer to that shared
memory object.
The name argument points to the shared memory object name, and must conform to the general construc-
tion rules for a pathname.
The oflag argument is the bitwise inclusive OR of the flags listed under Read-Write Flags and General
Flags (these flags are defined in the header file
<fcntl.h>).
The new file descriptor has the
FD_CLOEXEC flag set, and consequently does not remain open across
exec*() system calls.
Read-Write Flags
The value of oflag must be composed by taking the inclusive OR of exactly one of the following flags:
O_RDONLY Open for read access only.
O_RDWR Open for read and write access.
General Flags
Any combination of the following flags may also be used in setting the value of oflag.
O_CREAT If the shared memory object exists, this flag will have no effect, except as noted
under O_EXCL below. Otherwise the shared memory object is created; the shared
memory object’s user ID is set to the effective user ID of the process; the shared
memory object’s group ID is set to the effective group ID of the process. The shared
memory object’s permission bits is set to the value of the mode argument except
those set in the file mode creation mask of the process. The new shared memory
object will have a size of zero.
O_EXCL If O_EXCL and O_CREAT are set in oflag and the named shared memory object
exists, shm_open() will fail. The O_EXCL flag is ignored if O_CREAT is not set in
oflag.
O_TRUNC If the shared memory object exists, and it is successfully opened for reading and
writing (O_RDWR set in oflag), the object will be truncated to zero length. The mode
and owner shall remain unchanged by this function call.
RETURN VALUE
shm_open() returns the following values:
n Successful completion. n is the lowest numbered unused file descriptor for the process.
-1 Failure. errno is set to indicate the error.
ERRORS
If
shm_open() fails, errno is set to one of the following values:
[EACCES] The shared memory object exists and the permissions specified by oflag are denied,
or the shared memory object does not exist and permission to create the it is denied,
or
O_TRUNC is specified and write permission is denied.
[EEXIST] The
O_CREAT and O_EXCL are set in oflag and the named shared memory object
already exists.
[EINTR] The
shm_open() operation was interrupted by a signal.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1