// Copyright 2016 Tom Thorogood. All rights reserved.
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// Use of this source code is governed by a
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// Modified BSD License license that can be found in
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// the LICENSE file.
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// Package shm provides functions to open and unlink shared memory.
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package shm
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import (
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"os"
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"golang.org/x/sys/unix"
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)
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const devShm = "/dev/shm/"
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// Taken from shm_open(3):
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// shm_open() creates and opens a new, or opens an existing, POSIX shared
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// memory object. A POSIX shared memory object is in effect a handle which
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// can be used by unrelated processes to mmap(2) the same region of shared
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// memory. The shm_unlink() function performs the converse operation,
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// removing an object previously created by shm_open().
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//
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// The operation of shm_open() is analogous to that of open(2). name
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// specifies the shared memory object to be created or opened. For
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// portable use, a shared memory object should be identified by a name of
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// the form /somename; that is, a null-terminated string of up to NAME_MAX
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// (i.e., 255) characters consisting of an initial slash, followed by one
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// or more characters, none of which are slashes.
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func Open(name string, flag int, perm os.FileMode) (*os.File, error) {
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fileName := name
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for len(name) != 0 && name[0] == '/' {
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name = name[1:]
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}
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if len(name) == 0 {
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return nil, &os.PathError{Op: "open", Path: fileName, Err: unix.EINVAL}
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}
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o := uint32(perm.Perm())
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if perm&os.ModeSetuid != 0 {
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o |= unix.S_ISUID
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}
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if perm&os.ModeSetgid != 0 {
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o |= unix.S_ISGID
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}
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if perm&os.ModeSticky != 0 {
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o |= unix.S_ISVTX
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}
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fd, err := unix.Open(devShm+name, flag|unix.O_CLOEXEC, o)
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if err != nil {
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return nil, &os.PathError{Op: "open", Path: fileName, Err: err}
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}
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return os.NewFile(uintptr(fd), fileName), nil
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}
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// Taken from shm_unlink(3):
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// The operation of shm_unlink() is analogous to unlink(2): it removes a
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// shared memory object name, and, once all processes have unmapped the
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// object, de-allocates and destroys the contents of the associated memory
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// region. After a successful shm_unlink(), attempts to shm_open() an
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// object with the same name will fail (unless O_CREAT was specified, in
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// which case a new, distinct object is created).
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func Unlink(name string) error {
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fileName := name
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for len(name) != 0 && name[0] == '/' {
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name = name[1:]
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}
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if len(name) == 0 {
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return &os.PathError{Op: "unlink", Path: fileName, Err: unix.EINVAL}
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}
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if err := unix.Unlink(devShm + name); err != nil {
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return &os.PathError{Op: "unlink", Path: fileName, Err: err}
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}
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return nil
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}
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