cpython/Modules/fcntlmodule.c

/* fcntl module */

// Need limited C API version 3.13 for PyLong_AsInt()
#include "pyconfig.h"   // Py_GIL_DISABLED
#ifndef Py_GIL_DISABLED
#define Py_LIMITED_API …
#endif

#include "Python.h"

#include <errno.h>                // EINTR
#include <fcntl.h>                // fcntl()
#include <string.h>               // memcpy()
#include <sys/ioctl.h>            // ioctl()
#ifdef HAVE_SYS_FILE_H
#  include <sys/file.h>           // flock()
#endif
#ifdef HAVE_LINUX_FS_H
#  include <linux/fs.h>
#endif
#ifdef HAVE_STROPTS_H
#  include <stropts.h>            // I_FLUSHBAND
#endif

/*[clinic input]
module fcntl
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=124b58387c158179]*/

#include "clinic/fcntlmodule.c.h"

/*[clinic input]
fcntl.fcntl

    fd: fildes
    cmd as code: int
    arg: object(c_default='NULL') = 0
    /

Perform the operation `cmd` on file descriptor fd.

The values used for `cmd` are operating system dependent, and are available
as constants in the fcntl module, using the same names as used in
the relevant C header files.  The argument arg is optional, and
defaults to 0; it may be an int or a string.  If arg is given as a string,
the return value of fcntl is a string of that length, containing the
resulting value put in the arg buffer by the operating system.  The length
of the arg string is not allowed to exceed 1024 bytes.  If the arg given
is an integer or if none is specified, the result value is an integer
corresponding to the return value of the fcntl call in the C code.
[clinic start generated code]*/

static PyObject *
fcntl_fcntl_impl(PyObject *module, int fd, int code, PyObject *arg)
/*[clinic end generated code: output=888fc93b51c295bd input=7955340198e5f334]*/
{ … }


/*[clinic input]
fcntl.ioctl

    fd: fildes
    request as code: unsigned_long(bitwise=True)
    arg as ob_arg: object(c_default='NULL') = 0
    mutate_flag as mutate_arg: bool = True
    /

Perform the operation `request` on file descriptor `fd`.

The values used for `request` are operating system dependent, and are available
as constants in the fcntl or termios library modules, using the same names as
used in the relevant C header files.

The argument `arg` is optional, and defaults to 0; it may be an int or a
buffer containing character data (most likely a string or an array).

If the argument is a mutable buffer (such as an array) and if the
mutate_flag argument (which is only allowed in this case) is true then the
buffer is (in effect) passed to the operating system and changes made by
the OS will be reflected in the contents of the buffer after the call has
returned.  The return value is the integer returned by the ioctl system
call.

If the argument is a mutable buffer and the mutable_flag argument is false,
the behavior is as if a string had been passed.

If the argument is an immutable buffer (most likely a string) then a copy
of the buffer is passed to the operating system and the return value is a
string of the same length containing whatever the operating system put in
the buffer.  The length of the arg buffer in this case is not allowed to
exceed 1024 bytes.

If the arg given is an integer or if none is specified, the result value is
an integer corresponding to the return value of the ioctl call in the C
code.
[clinic start generated code]*/

static PyObject *
fcntl_ioctl_impl(PyObject *module, int fd, unsigned long code,
                 PyObject *ob_arg, int mutate_arg)
/*[clinic end generated code: output=3d8eb6828666cea1 input=cee70f6a27311e58]*/
{ … }

/*[clinic input]
fcntl.flock

    fd: fildes
    operation as code: int
    /

Perform the lock operation `operation` on file descriptor `fd`.

See the Unix manual page for flock(2) for details (On some systems, this
function is emulated using fcntl()).
[clinic start generated code]*/

static PyObject *
fcntl_flock_impl(PyObject *module, int fd, int code)
/*[clinic end generated code: output=84059e2b37d2fc64 input=0bfc00f795953452]*/
{ … }


/*[clinic input]
fcntl.lockf

    fd: fildes
    cmd as code: int
    len as lenobj: object(c_default='NULL') = 0
    start as startobj: object(c_default='NULL') = 0
    whence: int = 0
    /

A wrapper around the fcntl() locking calls.

`fd` is the file descriptor of the file to lock or unlock, and operation is one
of the following values:

    LOCK_UN - unlock
    LOCK_SH - acquire a shared lock
    LOCK_EX - acquire an exclusive lock

When operation is LOCK_SH or LOCK_EX, it can also be bitwise ORed with
LOCK_NB to avoid blocking on lock acquisition.  If LOCK_NB is used and the
lock cannot be acquired, an OSError will be raised and the exception will
have an errno attribute set to EACCES or EAGAIN (depending on the operating
system -- for portability, check for either value).

`len` is the number of bytes to lock, with the default meaning to lock to
EOF.  `start` is the byte offset, relative to `whence`, to that the lock
starts.  `whence` is as with fileobj.seek(), specifically:

    0 - relative to the start of the file (SEEK_SET)
    1 - relative to the current buffer position (SEEK_CUR)
    2 - relative to the end of the file (SEEK_END)
[clinic start generated code]*/

static PyObject *
fcntl_lockf_impl(PyObject *module, int fd, int code, PyObject *lenobj,
                 PyObject *startobj, int whence)
/*[clinic end generated code: output=4985e7a172e7461a input=5480479fc63a04b8]*/
{ … }

/* List of functions */

static PyMethodDef fcntl_methods[] = …;


PyDoc_STRVAR(module_doc,
"This module performs file control and I/O control on file\n\
descriptors.  It is an interface to the fcntl() and ioctl() Unix\n\
routines.  File descriptors can be obtained with the fileno() method of\n\
a file or socket object.");

/* Module initialisation */


static int
all_ins(PyObject* m)
{ … }

static int
fcntl_exec(PyObject *module)
{ … }

static PyModuleDef_Slot fcntl_slots[] = …;

static struct PyModuleDef fcntlmodule = …;

PyMODINIT_FUNC
PyInit_fcntl(void)
{ … }