mirror of
https://github.com/python/cpython.git
synced 2025-11-04 03:44:55 +00:00
23c0fb8edd
* Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module * Add pipesize parameter for subprocess.Popen class This will allow the user to control the size of the pipes. On linux the default is 64K. When a pipe is full it blocks for writing. When a pipe is empty it blocks for reading. On processes that are very fast this can lead to a lot of wasted CPU cycles. On a typical Linux system the max pipe size is 1024K which is much better. For high performance-oriented libraries such as xopen it is nice to be able to set the pipe size. The workaround without this feature is to use my_popen_process.stdout.fileno() in conjuction with fcntl and 1031 (value of F_SETPIPE_SZ) to acquire this behavior.
193 lines
8 KiB
ReStructuredText
193 lines
8 KiB
ReStructuredText
:mod:`fcntl` --- The ``fcntl`` and ``ioctl`` system calls
|
|
=========================================================
|
|
|
|
.. module:: fcntl
|
|
:platform: Unix
|
|
:synopsis: The fcntl() and ioctl() system calls.
|
|
|
|
.. sectionauthor:: Jaap Vermeulen
|
|
|
|
.. index::
|
|
pair: UNIX; file control
|
|
pair: UNIX; I/O control
|
|
|
|
----------------
|
|
|
|
This module performs file control and I/O control on file descriptors. It is an
|
|
interface to the :c:func:`fcntl` and :c:func:`ioctl` Unix routines. For a
|
|
complete description of these calls, see :manpage:`fcntl(2)` and
|
|
:manpage:`ioctl(2)` Unix manual pages.
|
|
|
|
All functions in this module take a file descriptor *fd* as their first
|
|
argument. This can be an integer file descriptor, such as returned by
|
|
``sys.stdin.fileno()``, or an :class:`io.IOBase` object, such as ``sys.stdin``
|
|
itself, which provides a :meth:`~io.IOBase.fileno` that returns a genuine file
|
|
descriptor.
|
|
|
|
.. versionchanged:: 3.3
|
|
Operations in this module used to raise an :exc:`IOError` where they now
|
|
raise an :exc:`OSError`.
|
|
|
|
.. versionchanged:: 3.8
|
|
The fcntl module now contains ``F_ADD_SEALS``, ``F_GET_SEALS``, and
|
|
``F_SEAL_*`` constants for sealing of :func:`os.memfd_create` file
|
|
descriptors.
|
|
|
|
.. versionchanged:: 3.9
|
|
On macOS, the fcntl module exposes the ``F_GETPATH`` constant, which obtains
|
|
the path of a file from a file descriptor.
|
|
On Linux(>=3.15), the fcntl module exposes the ``F_OFD_GETLK``, ``F_OFD_SETLK``
|
|
and ``F_OFD_SETLKW`` constants, which working with open file description locks.
|
|
|
|
.. versionchanged:: 3.10
|
|
On Linux >= 2.6.11, the fcntl module exposes the ``F_GETPIPE_SZ`` and
|
|
``F_SETPIPE_SZ`` constants, which allow to check and modify a pipe's size
|
|
respectively.
|
|
|
|
The module defines the following functions:
|
|
|
|
|
|
.. function:: fcntl(fd, cmd, arg=0)
|
|
|
|
Perform the operation *cmd* on file descriptor *fd* (file objects providing
|
|
a :meth:`~io.IOBase.fileno` method are accepted as well). The values used
|
|
for *cmd* are operating system dependent, and are available as constants
|
|
in the :mod:`fcntl` module, using the same names as used in the relevant C
|
|
header files. The argument *arg* can either be an integer value, or a
|
|
:class:`bytes` object. With an integer value, the return value of this
|
|
function is the integer return value of the C :c:func:`fcntl` call. When
|
|
the argument is bytes it represents a binary structure, e.g. created by
|
|
:func:`struct.pack`. The binary data is copied to a buffer whose address is
|
|
passed to the C :c:func:`fcntl` call. The return value after a successful
|
|
call is the contents of the buffer, converted to a :class:`bytes` object.
|
|
The length of the returned object will be the same as the length of the
|
|
*arg* argument. This is limited to 1024 bytes. If the information returned
|
|
in the buffer by the operating system is larger than 1024 bytes, this is
|
|
most likely to result in a segmentation violation or a more subtle data
|
|
corruption.
|
|
|
|
If the :c:func:`fcntl` fails, an :exc:`OSError` is raised.
|
|
|
|
.. audit-event:: fcntl.fcntl fd,cmd,arg fcntl.fcntl
|
|
|
|
|
|
.. function:: ioctl(fd, request, arg=0, mutate_flag=True)
|
|
|
|
This function is identical to the :func:`~fcntl.fcntl` function, except
|
|
that the argument handling is even more complicated.
|
|
|
|
The *request* parameter is limited to values that can fit in 32-bits.
|
|
Additional constants of interest for use as the *request* argument can be
|
|
found in the :mod:`termios` module, under the same names as used in
|
|
the relevant C header files.
|
|
|
|
The parameter *arg* can be one of an integer, an object supporting the
|
|
read-only buffer interface (like :class:`bytes`) or an object supporting
|
|
the read-write buffer interface (like :class:`bytearray`).
|
|
|
|
In all but the last case, behaviour is as for the :func:`~fcntl.fcntl`
|
|
function.
|
|
|
|
If a mutable buffer is passed, then the behaviour is determined by the value of
|
|
the *mutate_flag* parameter.
|
|
|
|
If it is false, the buffer's mutability is ignored and behaviour is as for a
|
|
read-only buffer, except that the 1024 byte limit mentioned above is avoided --
|
|
so long as the buffer you pass is at least as long as what the operating system
|
|
wants to put there, things should work.
|
|
|
|
If *mutate_flag* is true (the default), then the buffer is (in effect) passed
|
|
to the underlying :func:`ioctl` system call, the latter's return code is
|
|
passed back to the calling Python, and the buffer's new contents reflect the
|
|
action of the :func:`ioctl`. This is a slight simplification, because if the
|
|
supplied buffer is less than 1024 bytes long it is first copied into a static
|
|
buffer 1024 bytes long which is then passed to :func:`ioctl` and copied back
|
|
into the supplied buffer.
|
|
|
|
If the :c:func:`ioctl` fails, an :exc:`OSError` exception is raised.
|
|
|
|
An example::
|
|
|
|
>>> import array, fcntl, struct, termios, os
|
|
>>> os.getpgrp()
|
|
13341
|
|
>>> struct.unpack('h', fcntl.ioctl(0, termios.TIOCGPGRP, " "))[0]
|
|
13341
|
|
>>> buf = array.array('h', [0])
|
|
>>> fcntl.ioctl(0, termios.TIOCGPGRP, buf, 1)
|
|
0
|
|
>>> buf
|
|
array('h', [13341])
|
|
|
|
.. audit-event:: fcntl.ioctl fd,request,arg fcntl.ioctl
|
|
|
|
|
|
.. function:: flock(fd, operation)
|
|
|
|
Perform the lock operation *operation* on file descriptor *fd* (file objects providing
|
|
a :meth:`~io.IOBase.fileno` method are accepted as well). See the Unix manual
|
|
:manpage:`flock(2)` for details. (On some systems, this function is emulated
|
|
using :c:func:`fcntl`.)
|
|
|
|
If the :c:func:`flock` fails, an :exc:`OSError` exception is raised.
|
|
|
|
.. audit-event:: fcntl.flock fd,operation fcntl.flock
|
|
|
|
|
|
.. function:: lockf(fd, cmd, len=0, start=0, whence=0)
|
|
|
|
This is essentially a wrapper around the :func:`~fcntl.fcntl` locking calls.
|
|
*fd* is the file descriptor (file objects providing a :meth:`~io.IOBase.fileno`
|
|
method are accepted as well) of the file to lock or unlock, and *cmd*
|
|
is one of the following values:
|
|
|
|
* :const:`LOCK_UN` -- unlock
|
|
* :const:`LOCK_SH` -- acquire a shared lock
|
|
* :const:`LOCK_EX` -- acquire an exclusive lock
|
|
|
|
When *cmd* is :const:`LOCK_SH` or :const:`LOCK_EX`, it can also be
|
|
bitwise ORed with :const:`LOCK_NB` to avoid blocking on lock acquisition.
|
|
If :const:`LOCK_NB` is used and the lock cannot be acquired, an
|
|
:exc:`OSError` will be raised and the exception will have an *errno*
|
|
attribute set to :const:`EACCES` or :const:`EAGAIN` (depending on the
|
|
operating system; for portability, check for both values). On at least some
|
|
systems, :const:`LOCK_EX` can only be used if the file descriptor refers to a
|
|
file opened for writing.
|
|
|
|
*len* is the number of bytes to lock, *start* is the byte offset at
|
|
which the lock starts, relative to *whence*, and *whence* is as with
|
|
:func:`io.IOBase.seek`, specifically:
|
|
|
|
* :const:`0` -- relative to the start of the file (:data:`os.SEEK_SET`)
|
|
* :const:`1` -- relative to the current buffer position (:data:`os.SEEK_CUR`)
|
|
* :const:`2` -- relative to the end of the file (:data:`os.SEEK_END`)
|
|
|
|
The default for *start* is 0, which means to start at the beginning of the file.
|
|
The default for *len* is 0 which means to lock to the end of the file. The
|
|
default for *whence* is also 0.
|
|
|
|
.. audit-event:: fcntl.lockf fd,cmd,len,start,whence fcntl.lockf
|
|
|
|
Examples (all on a SVR4 compliant system)::
|
|
|
|
import struct, fcntl, os
|
|
|
|
f = open(...)
|
|
rv = fcntl.fcntl(f, fcntl.F_SETFL, os.O_NDELAY)
|
|
|
|
lockdata = struct.pack('hhllhh', fcntl.F_WRLCK, 0, 0, 0, 0, 0)
|
|
rv = fcntl.fcntl(f, fcntl.F_SETLKW, lockdata)
|
|
|
|
Note that in the first example the return value variable *rv* will hold an
|
|
integer value; in the second example it will hold a :class:`bytes` object. The
|
|
structure lay-out for the *lockdata* variable is system dependent --- therefore
|
|
using the :func:`flock` call may be better.
|
|
|
|
|
|
.. seealso::
|
|
|
|
Module :mod:`os`
|
|
If the locking flags :data:`~os.O_SHLOCK` and :data:`~os.O_EXLOCK` are
|
|
present in the :mod:`os` module (on BSD only), the :func:`os.open`
|
|
function provides an alternative to the :func:`lockf` and :func:`flock`
|
|
functions.
|