Standard C Library Functions shmopen(3C)
NAME
shmopen - open a shared memory object
SYNOPSIS
#include
int shmopen(const char *name, int oflag, modet mode);
DESCRIPTION
The shmopen() function establishes a connection between a
shared memory object and a file descriptor. It creates an
open file description that refers to the shared memory
object and a file descriptor that refers to that open file
description. The file descriptor is used by other functions
to refer to that shared memory object. The name argument
points to a string naming a shared memory object. It is
unspecified whether the name appears in the file system and
is visible to other functions that take pathnames as argu-
ments. The name argument conforms to the construction rules
for a pathname. The first character of name must be a slash
(/) character and the remaining characters of name cannot
include any slash characters. For maximum portability,
name should include no more than 14 characters, but this
limit is not enforced.
If successful, shmopen() returns a file descriptor for the
shared memory object that is the lowest numbered file
descriptor not currently open for that process. The open
file description is new, and therefore the file descriptor
does not share it with any other processes. It is unspeci-
fied whether the file offset is set. The FDCLOEXEC file
descriptor flag associated with the new file descriptor is
set.
The file status flags and file access modes of the open file
description are according to the value of oflag. The oflag
argument is the bitwise inclusive OR of the following flags
defined in the header . Applications specify
exactly one of the first two values (access modes) below in
the value of oflag:
ORDONLY Open for read access only.
ORDWR Open for read or write access.
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Standard C Library Functions shmopen(3C)
Any combination of the remaining flags may be specified in
the value of oflag:
OCREAT If the shared memory object exists, this flag
has no effect, except as noted under OEXCL
below. Otherwise the shared memory object is
created; the user ID of the shared memory object
will be set to the effective user ID of the pro-
cess; the group ID of the shared memory object
will be set to a system default group ID or to
the effective group ID of the process. The per-
mission bits of the shared memory object will be
set to the value of the mode argument except
those set in the file mode creation mask of the
process. When bits in mode other than the file
permission bits are set, the effect is unspeci-
fied. The mode argument does not affect whether
the shared memory object is opened for reading,
for writing, or for both. The shared memory
object has a size of zero.
OEXCL If OEXCL and OCREAT are set, shmopen() fails
if the shared memory object exists. The check
for the existence of the shared memory object
and the creation of the object if it does not
exist is atomic with respect to other processes
executing shmopen() naming the same shared
memory object with OEXCL and OCREAT set. If
OEXCL is set and OCREAT is not set, the result
is undefined.
OTRUNC If the shared memory object exists, and it is
successfully opened ORDWR, the object will be
truncated to zero length and the mode and owner
will be unchanged by this function call. The
result of using OTRUNC with ORDONLY is unde-
fined.
When a shared memory object is created, the state of the
shared memory object, including all data associated with the
shared memory object, persists until the shared memory
object is unlinked and all other references are gone. It is
unspecified whether the name and shared memory object state
remain valid after a system reboot.
RETURN VALUES
Upon successful completion, the shmopen() function returns
a non-negative integer representing the lowest numbered
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Standard C Library Functions shmopen(3C)
unused file descriptor. Otherwise, it returns -1 and sets
errno to indicate the error condition.
ERORS
The shmopen() function will fail if:
EACES 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 shared memory
object is denied, or OTRUNC is specified
and write permission is denied.
EXIST OCREAT and OEXCL are set and the named
shared memory object already exists.
EINTR The shmopen() operation was interrupted by
a signal.
EINVAL The shmopen() operation is not supported
for the given name.
EMFILE Too many file descriptors are currently in
use by this process.
ENAMETOLONG The length of the name string exceeds
PATHMAX, or a pathname component is longer
than NAMEMAX while POSIXNOTRUNC is in
effect.
ENFILE Too many shared memory objects are
currently open in the system.
ENOENT OCREAT is not set and the named shared
memory object does not exist.
ENOSPC There is insufficient space for the crea-
tion of the new shared memory object.
ENOSYS The shmopen() function is not supported by
the system.
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Standard C Library Functions shmopen(3C)
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Committed
MT-Level MT-Safe
Standard See standards(5).
SEE ALSO
close(2), dup(2), exec(2), fcntl(2), mmap(2), umask(2),
shmunlink(3C), sysconf(3C), fcntl.h(3HEAD), attributes(5),
standards(5)
NOTES
Solaris 2.6 was the first release to support the Asynchro-
nous Input and Output option. Prior to this release, this
function always returned -1 and set errno to ENOSYS.
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