fcntl — fcntl and ioctl 系统调用

This module performs file and I/O control on file descriptors. It is an interface to the fcntl() and ioctl() Unix routines. See the fcntl(2) and ioctl(2) Unix manual pages for full details.

可用性 ：Unix，非 WASI。

本模块中的所有函数接受文件描述符 fd 作为其第 1 自变量。这可以是整数文件描述符，譬如返回通过 sys.stdin.fileno() ，或 io.IOBase 对象，譬如 sys.stdin 自身，其提供 fileno() 返回真正的文件描述符。

3.3 版改变： 使用此模块中的操作引发 IOError 它们现在引发 OSError .

3.8 版改变： The fcntl module now contains F_ADD_SEALS , F_GET_SEALS ，和 F_SEAL_* 常量为密封 os.memfd_create() 文件描述符。

3.9 版改变： 在 macOS， 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 are used when working with open file description locks.

3.10 版改变： 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.

3.11 版改变： On FreeBSD, the fcntl module exposes the F_DUP2FD and F_DUP2FD_CLOEXEC constants, which allow to duplicate a file descriptor, the latter setting FD_CLOEXEC flag in addition.

3.12 版改变： On Linux >= 4.5, the fcntl module exposes the FICLONE and FICLONERANGE constants, which allow to share some data of one file with another file by reflinking on some filesystems (e.g., btrfs, OCFS2, and XFS). This behavior is commonly referred to as “copy-on-write”.

Changed in version 3.13: On Linux >= 2.6.32, the fcntl module exposes the F_GETOWN_EX , F_SETOWN_EX , F_OWNER_TID , F_OWNER_PID , F_OWNER_PGRP constants, which allow to direct I/O availability signals to a specific thread, process, or process group. On Linux >= 4.13, the fcntl module exposes the F_GET_RW_HINT , F_SET_RW_HINT , F_GET_FILE_RW_HINT , F_SET_FILE_RW_HINT ，和 RWH_WRITE_LIFE_* constants, which allow to inform the kernel about the relative expected lifetime of writes on a given inode or via a particular open file description. On Linux >= 5.1 and NetBSD, the fcntl module exposes the F_SEAL_FUTURE_WRITE constant for use with F_ADD_SEALS and F_GET_SEALS operations. On FreeBSD, the fcntl module exposes the F_READAHEAD , F_ISUNIONSTACK ，和 F_KINFO constants. On macOS and FreeBSD, the fcntl module exposes the F_RDAHEAD constant. On NetBSD and AIX, the fcntl module exposes the F_CLOSEM constant. On NetBSD, the fcntl module exposes the F_MAXFD constant. On macOS and NetBSD, the fcntl module exposes the F_GETNOSIGPIPE and F_SETNOSIGPIPE 常量。

模块定义了下列函数：

fcntl. fcntl ( fd , cmd , arg = 0 )

履行操作 cmd 对于文件描述符 fd (文件对象提供 fileno() method are accepted as well). 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 can either be an integer value, or a bytes object. With an integer value, the return value of this function is the integer return value of the C fcntl() call. When the argument is bytes it represents a binary structure, e.g. created by struct.pack() . The binary data is copied to a buffer whose address is passed to the C fcntl() call. The return value after a successful call is the contents of the buffer, converted to a 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.

若 fcntl() call fails, an OSError 被引发。

引发 审计事件 fcntl.fcntl 采用自变量 fd , cmd , arg .

fcntl. ioctl ( fd , request , arg = 0 , mutate_flag = True )

此函数等同于 fcntl() 函数，除自变量处理甚至更复杂外。

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 termios module, under the same names as used in the relevant C header files.

参数 arg can be one of an integer, an object supporting the read-only buffer interface (like bytes ) or an object supporting the read-write buffer interface (like bytearray ).

In all but the last case, behaviour is as for the fcntl() 函数。

If a mutable buffer is passed, then the behaviour is determined by the value of the mutate_flag 参数。

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.

若 mutate_flag 为 True (默认)，那么 (实际上) 会将缓冲传递给底层 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 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 ioctl() and copied back into the supplied buffer.

若 ioctl() call fails, an OSError 异常被引发。

范例： 

>>> 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])