сделать специальный файл FIFO (make a FIFO special file)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
mkfifo, mkfifoat — make a FIFO special file
Синопсис (Synopsis)
#include <sys/stat.h>
int mkfifo(const char *path, mode_t mode);
#include <fcntl.h>
int mkfifoat(int fd, const char *path, mode_t mode);
Описание (Description)
The mkfifo() function shall create a new FIFO special file named
by the pathname pointed to by path. The file permission bits of
the new FIFO shall be initialized from mode. The file permission
bits of the mode argument shall be modified by the process' file
creation mask.
When bits in mode other than the file permission bits are set,
the effect is implementation-defined.
If path names a symbolic link, mkfifo() shall fail and set errno
to [EEXIST].
The FIFO's user ID shall be set to the process' effective user
ID. The FIFO's group ID shall be set to the group ID of the
parent directory or to the effective group ID of the process.
Implementations shall provide a way to initialize the FIFO's
group ID to the group ID of the parent directory. Implementations
may, but need not, provide an implementation-defined way to
initialize the FIFO's group ID to the effective group ID of the
calling process.
Upon successful completion, mkfifo() shall mark for update the
last data access, last data modification, and last file status
change timestamps of the file. Also, the last data modification
and last file status change timestamps of the directory that
contains the new entry shall be marked for update.
The mkfifoat() function shall be equivalent to the mkfifo()
function except in the case where path specifies a relative path.
In this case the newly created FIFO is created relative to the
directory associated with the file descriptor fd instead of the
current working directory. If the access mode of the open file
description associated with the file descriptor is not O_SEARCH,
the function shall check whether directory searches are permitted
using the current permissions of the directory underlying the
file descriptor. If the access mode is O_SEARCH, the function
shall not perform the check.
If mkfifoat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory shall be used and the
behavior shall be identical to a call to mkfifo().
Возвращаемое значение (Return value)
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error. If -1 is returned, no FIFO shall be created.
Ошибки (Error)
These functions shall fail if:
EACCES A component of the path prefix denies search permission,
or write permission is denied on the parent directory of
the FIFO to be created.
EEXIST The named file already exists.
ELOOP A loop exists in symbolic links encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of the path prefix of path does not name an
existing file or path is an empty string.
ENOENT or ENOTDIR
The path argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters. If path without the trailing <slash>
characters would name an existing file, an [ENOENT] error
shall not occur.
ENOSPC The directory that would contain the new file cannot be
extended or the file system is out of file-allocation
resources.
ENOTDIR
A component of the path prefix names an existing file that
is neither a directory nor a symbolic link to a directory.
EROFS The named file resides on a read-only file system.
The mkfifoat() function shall fail if:
EACCES The access mode of the open file description associated
with fd is not O_SEARCH and the permissions of the
directory underlying fd do not permit directory searches.
EBADF The path argument does not specify an absolute path and
the fd argument is neither AT_FDCWD nor a valid file
descriptor open for reading or searching.
ENOTDIR
The path argument is not an absolute path and fd is a file
descriptor associated with a non-directory file.
These functions may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
The following sections are informative.
Примеры (Examples)
Creating a FIFO File
The following example shows how to create a FIFO file named
/home/cnd/mod_done, with read/write permissions for owner, and
with read permissions for group and others.
#include <sys/types.h>
#include <sys/stat.h>
int status;
...
status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
S_IRGRP | S_IROTH);
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
The syntax of this function is intended to maintain compatibility
with historical implementations of mknod(). The latter function
was included in the 1984 /usr/group standard but only for use in
creating FIFO special files. The mknod() function was originally
excluded from the POSIX.1‐1988 standard as implementation-defined
and replaced by mkdir() and mkfifo(). The mknod() function is
now included for alignment with the Single UNIX Specification.
The POSIX.1‐1990 standard required that the group ID of a newly
created FIFO be set to the group ID of its parent directory or to
the effective group ID of the creating process. FIPS 151‐2
required that implementations provide a way to have the group ID
be set to the group ID of the containing directory, but did not
prohibit implementations also supporting a way to set the group
ID to the effective group ID of the creating process. Conforming
applications should not assume which group ID will be used. If it
matters, an application can use chown() to set the group ID after
the FIFO is created, or determine under what conditions the
implementation will set the desired group ID.
The purpose of the mkfifoat() function is to create a FIFO
special file in directories other than the current working
directory without exposure to race conditions. Any part of the
path of a file could be changed in parallel to a call to
mkfifo(), resulting in unspecified behavior. By opening a file
descriptor for the target directory and using the mkfifoat()
function it can be guaranteed that the newly created FIFO is
located relative to the desired directory.
Будущие направления (Future directions)
None.
Смотри также (See also)
chmod(3p), mknod(3p), umask(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
sys_stat.h(0p), sys_types.h(0p)
