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.TH SHM_OPEN 3C "Feb 5, 2008"
.SH NAME
shm_open \- open a shared memory object
.SH SYNOPSIS
.LP
.nf
#include <sys/mman.h>

\fBint\fR \fBshm_open\fR(\fBconst char *\fR\fIname\fR, \fBint\fR \fIoflag\fR, \fBmode_t\fR \fImode\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBshm_open()\fR 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 \fIname\fR 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 arguments. The
\fIname\fR argument conforms to the construction rules for a pathname. The
first character of  \fIname\fR must be a slash  (/) character and the remaining
characters of  \fIname\fR cannot include any slash characters.  For maximum
portability,  \fIname\fR should include no more than 14 characters, but this
limit is not enforced.
.sp
.LP
If successful, \fBshm_open()\fR 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 unspecified whether the file
offset is set. The \fBFD_CLOEXEC\fR file descriptor flag associated with the
new file descriptor is set.
.sp
.LP
The file status flags and file access modes of the open file description are
according to the value of \fIoflag\fR. The \fIoflag\fR argument is the bitwise
inclusive OR of the following flags defined in the header <\fBfcntl.h\fR>.
Applications specify exactly one of the first two values (access modes) below
in the value of \fIoflag\fR:
.sp
.ne 2
.na
\fB\fBO_RDONLY\fR \fR
.ad
.RS 13n
Open for read access only.
.RE

.sp
.ne 2
.na
\fB\fBO_RDWR\fR \fR
.ad
.RS 13n
Open for read or write access.
.RE

.sp
.LP
Any combination of the remaining flags may be specified in the value of
\fIoflag\fR:
.sp
.ne 2
.na
\fB\fBO_CREAT\fR \fR
.ad
.RS 12n
If the shared memory object exists, this flag has no effect, except as noted
under \fBO_EXCL\fR below. Otherwise the shared memory object is created; the
user \fBID\fR of the shared memory object will be set to the effective user
\fBID\fR of the process; the group \fBID\fR of the shared memory object will be
set to a system default group \fBID\fR or to the effective group \fBID\fR of
the process. The permission bits of the shared memory object will be set to the
value of the \fImode\fR argument except those set in the file mode creation
mask of the process. When bits in \fImode\fR other than the file permission
bits are set, the effect is unspecified. The \fImode\fR 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.
.RE

.sp
.ne 2
.na
\fB\fBO_EXCL\fR \fR
.ad
.RS 12n
If \fBO_EXCL\fR and \fBO_CREAT\fR are set, \fBshm_open()\fR 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 \fBshm_open()\fR naming the same shared memory object
with \fBO_EXCL\fR and \fBO_CREAT\fR set. If \fBO_EXCL\fR is set and
\fBO_CREAT\fR is not set, the result is undefined.
.RE

.sp
.ne 2
.na
\fB\fBO_TRUNC\fR \fR
.ad
.RS 12n
If the shared memory object exists, and it is successfully opened \fBO_RDWR\fR,
the object will be truncated to zero length and the mode and owner will be
unchanged by this function call. The result of using \fBO_TRUNC\fR with
\fBO_RDONLY\fR is undefined.
.RE

.sp
.LP
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.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, the \fBshm_open()\fR function returns a
non-negative integer representing the lowest numbered unused file descriptor.
Otherwise, it returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error
condition.
.SH ERRORS
.sp
.LP
The \fBshm_open()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR \fR
.ad
.RS 17n
The shared memory object exists and the permissions specified by \fIoflag\fR
are denied, or the shared memory object does not exist and permission to create
the shared memory object is denied, or \fBO_TRUNC\fR is specified and write
permission is denied.
.RE

.sp
.ne 2
.na
\fB\fBEEXIST\fR \fR
.ad
.RS 17n
\fBO_CREAT\fR and \fBO_EXCL\fR are set and the named shared memory object
already exists.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR \fR
.ad
.RS 17n
The \fBshm_open()\fR operation was interrupted by a signal.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 17n
The \fBshm_open()\fR operation is not supported for the given name.
.RE

.sp
.ne 2
.na
\fB\fBEMFILE\fR \fR
.ad
.RS 17n
Too many file descriptors are currently in use by this process.
.RE

.sp
.ne 2
.na
\fB\fBENAMETOOLONG\fR \fR
.ad
.RS 17n
The length of the \fIname\fR string exceeds \fBPATH_MAX\fR, or a pathname
component is longer than \fINAME_MAX\fR while \fB_POSIX_NO_TRUNC\fR is in
effect.
.RE

.sp
.ne 2
.na
\fB\fBENFILE\fR \fR
.ad
.RS 17n
Too many shared memory objects are currently open in the system.
.RE

.sp
.ne 2
.na
\fB\fBENOENT\fR \fR
.ad
.RS 17n
\fBO_CREAT\fR is not set and the named shared memory object does not exist.
.RE

.sp
.ne 2
.na
\fB\fBENOSPC\fR \fR
.ad
.RS 17n
There is insufficient space for the creation of the new shared memory object.
.RE

.sp
.ne 2
.na
\fB\fBENOSYS\fR \fR
.ad
.RS 17n
The \fBshm_open()\fR function is not supported by the system.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See \fBstandards\fR(5).
.TE

.SH SEE ALSO
.sp
.LP
\fBclose\fR(2), \fBdup\fR(2), \fBexec\fR(2), \fBfcntl\fR(2), \fBmmap\fR(2),
\fBumask\fR(2), \fBshm_unlink\fR(3C), \fBsysconf\fR(3C), \fBfcntl.h\fR(3HEAD),
\fBattributes\fR(5), \fBstandards\fR(5)
.SH NOTES
.sp
.LP
Solaris 2.6 was the first release to support the Asynchronous Input and Output
option. Prior to this release, this function always returned \fB\(mi1\fR and
set \fBerrno\fR to \fBENOSYS\fR.