Gamma™ : Version 6.4
	OS APIs

`shm_open`

shm_open — opens shared memory objects.

Syntax

shm_open (share_name, open_flags, create_mode, size?)

Arguments

share_name: The name of the shared memory object.
open_flags: Open control flags.
create_mode: Creation mode.
size: The size of the shared object in bytes.

Returns

A handle to the shared memory object, or nil on failure.

Description

This function is a wrapper for the C function shm_open. It is currently only available in QNX 4.

The name of the shared memory object is usually a name found under the /dev/shmem directory. Direct shared memory access to devices is acheived through a shm_open call to the existing Physical shared memory.

If you are accessing the existing Physical shared memory region (/dev/shmem/Physical) DO NOT use the size argument, as you may inadvertantly resize this shared memory. The size argument is added as a convenience, and can be used to specify the size of a newly created object.

Valid open-flags are OR-ed combinations of:

O_RDONLY open for read-only

O_RDWR open for read and write access

O_CREAT create a new shared memory segment with access privledges governed by the create_mode parameter

O_EXCL Exclusive mode. If O_EXCL and O_CREAT are set then shm_open will fail if the shared memory segment exists.

O_TRUNC If the shared memory object exists, and it is successfully opened O_RDWR, the object is truncated to zero length and the mode and owner are unchanged.

The creation mode is usually an octal number in the range 0o000 - 0o777 defining the access privledges for the shared memory object. Require the 'const/filesys' file to load constants to make this arg easier

Possible errno values are:

EACCESS permission to create the shared memory object denied

EEXIST O_CREAT and O_EXCL are set and the named shared memory object already exists

EINTR The function call was interrupted by a signal

EMFILE Too many file descriptors in use by this process

ENAMETOOLONG The lengthof the name arg is too long

ENFILE To 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, or O_CREAT is set and either the name prefix does not exist or the name arg is an empty string

ENOSPC Not enough space for the creation of the new shared memory object

ENOSYS This function is not supported by this implementation.

Example

//This code maps the first 1000 bytes from video
//memory (0xA0000) into a buffer named buf.

require_lisp("const/filesys");
require_lisp("const/mman");
fd = shm_open("Physical",O_RDONLY, 0o777);
buf = mmap(1000, PROT_READ , MAP_SHARED, fd, 0xA0000);


setenv		shm_unlink

shm_open