Standard C Library Functions shm_open(3C)
NAME
shm_open - open a shared memory object
SYNOPSIS
#include
int shm_open(const char *name, int oflag, mode_t mode);
DESCRIPTION
The shm_open() 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 andis 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, shm_open() 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 descriptordoes not share it with any other processes. It is unspeci-
fied whether the file offset is set. The FD_CLOEXEC 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: O_RDONLY Open for read access only.
O_RDWR Open for read or write access.
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Standard C Library Functions shm_open(3C)
Any combination of the remaining flags may be specified in the value of oflag:O_CREAT If the shared memory object exists, this flag
has no effect, except as noted under O_EXCL
below. Otherwise the shared memory object is created; the user ID of the shared memory objectwill 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 tothe 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 filepermission 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.O_EXCL If O_EXCL and O_CREAT are set, shm_open() 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 processesexecuting shm_open() naming the same shared
memory object with O_EXCL and O_CREAT set. If
O_EXCL is set and O_CREAT is not set, the result
is undefined.O_TRUNC If the shared memory object exists, and it is
successfully opened O_RDWR, the object will be
truncated to zero length and the mode and owner will be unchanged by this function call. Theresult of using O_TRUNC with O_RDONLY 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 shm_open() function returns
a non-negative integer representing the lowest numbered
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Standard C Library Functions shm_open(3C)
unused file descriptor. Otherwise, it returns -1 and sets
errno to indicate the error condition.ERRORS
The shm_open() function will fail if:
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 shared memoryobject is denied, or O_TRUNC is specified
and write permission is denied.EEXIST O_CREAT and O_EXCL are set and the named
shared memory object already exists.EINTR The shm_open() operation was interrupted by
a signal.EINVAL The shm_open() operation is not supported
for the given name. EMFILE Too many file descriptors are currently in use by this process.ENAMETOOLONG The length of the name string exceeds
PATH_MAX, or a pathname component is longer
than NAME_MAX while _POSIX_NO_TRUNC is in
effect. ENFILE Too many shared memory objects are currently open in the system.ENOENT O_CREAT 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 shm_open() function is not supported by
the system.SunOS 5.11 Last change: 5 Feb 2008 3
Standard C Library Functions shm_open(3C)
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE 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),shm_unlink(3C), sysconf(3C), fcntl.h(3HEAD), attributes(5),
standards(5) NOTESSolaris 2.6 was the first release to support the Asynchro-
nous Input and Output option. Prior to this release, thisfunction always returned -1 and set errno to ENOSYS.
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