"fcntl" --- The "fcntl" and "ioctl" system calls
************************************************

======================================================================

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.

가용성: Unix, not WASI.

이 모듈의 모든 함수는 첫 번째 인자로 파일 기술자 *fd*를 받아들입니다.
이것은 "sys.stdin.fileno()"에 의해 반환된 것과 같은 정수 파일 기술자이
거나 "sys.stdin" 자체와 같은 "io.IOBase" 객체일 수 있습니다. 이 객체는
실제 파일 기술자를 반환하는 "fileno()"를 제공합니다.

버전 3.3에서 변경: 이 모듈의 연산은 "IOError"를 발생시켰는데, 이제는
"OSError"를 발생시킵니다.

버전 3.8에서 변경: The "fcntl" module now contains "F_ADD_SEALS",
"F_GET_SEALS", and "F_SEAL_*" constants for sealing of
"os.memfd_create()" file descriptors.

버전 3.9에서 변경: 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 are
used when working with open file description locks.

버전 3.10에서 변경: 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.

버전 3.11에서 변경: 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.

버전 3.12에서 변경: 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".

버전 3.13에서 변경: 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", and "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", and "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" constant.

이 모듈은 다음 함수를 정의합니다:

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

   Perform the operation *cmd* on file descriptor *fd* (file objects
   providing a "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, a "bytes" object, or a string. The type and size of
   *arg* must match the type and size of the argument of the operation
   as specified in the relevant C documentation.

   When *arg* is an integer, the function returns the integer return
   value of the C "fcntl()" call.

   When the argument is bytes, it represents a binary structure, for
   example, created by "struct.pack()". A string value is encoded to
   binary using the UTF-8 encoding. 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 "fcntl()" call fails, an "OSError" is raised.

   참고:

     If the type or the size of *arg* does not match the type or size
     of the argument of the operation (for example, if an integer is
     passed when a pointer is expected, or 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.

   인자 "fd", "cmd", "arg"로 감사 이벤트 "fcntl.fcntl"을 발생시킵니다.

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

   이 함수는 인자 처리가 훨씬 더 복잡하다는 점을 제외하면, "fcntl()"
   함수와 같습니다.

   The *request* parameter is limited to values that can fit in
   32-bits or 64-bits, depending on the platform. 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.

   The parameter *arg* can be an integer, a *bytes-like object*, or a
   string. The type and size of *arg* must match the type and size of
   the argument of the operation as specified in the relevant C
   documentation.

   If *arg* does not support the read-write buffer interface or the
   *mutate_flag* is false, behavior is as for the "fcntl()" function.

   If *arg* supports the read-write buffer interface (like
   "bytearray") and *mutate_flag* is true (the default), then the
   buffer is (in effect) passed to the underlying "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.

   If the "ioctl()" call fails, an "OSError" exception is raised.

   참고:

     If the type or size of *arg* does not match the type or size of
     the operation's argument (for example, if an integer is passed
     when a pointer is expected, or the information returned in the
     buffer by the operating system is larger than 1024 bytes, or the
     size of the mutable bytes-like object is too small), this is most
     likely to result in a segmentation violation or a more subtle
     data corruption.

   예제:

      >>> 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])

   인자 "fd", "request", "arg"로 감사 이벤트 "fcntl.ioctl"을 발생시킵
   니다.

fcntl.flock(fd, operation, /)

   파일 기술자 *fd*("fileno()" 메서드를 제공하는 파일 객체도 허용됩니
   다)에 대한 잠금 연산 *operation*을 수행합니다. 자세한 내용은 유닉스
   매뉴얼 *flock(2)*를 참조하십시오. (일부 시스템에서는, 이 함수가
   "fcntl()"를 사용하여 에뮬레이트됩니다.)

   If the "flock()" call fails, an "OSError" exception is raised.

   인자 "fd", "operation"으로 감사 이벤트 "fcntl.flock"을 발생시킵니다
   .

fcntl.lockf(fd, cmd, len=0, start=0, whence=0, /)

   이것은 본질에서 "fcntl()" 잠금 호출에 대한 래퍼입니다. *fd*는 잠그
   거나 잠금 해제할 파일의 파일 기술자이고 ("fileno()" 메서드를 제공하
   는 파일 객체도 허용됩니다), *cmd*는 다음 값 중 하나입니다:

   fcntl.LOCK_UN

      Release an existing lock.

   fcntl.LOCK_SH

      Acquire a shared lock.

   fcntl.LOCK_EX

      Acquire an exclusive lock.

   fcntl.LOCK_NB

      Bitwise OR with any of the other three "LOCK_*" constants to
      make the request non-blocking.

   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 both values).  On at least some systems,
   "LOCK_EX" can only be used if the file descriptor refers to a file
   opened for writing.

   *len*은 잠글 바이트 수, *start*는 *whence*가 정의하는 기준으로 잠금
   이 시작되는 바이트 오프셋이며 *whence*는 "io.IOBase.seek()"에서와
   같은데, 구체적으로 다음과 같습니다:

   * "0" -- relative to the start of the file ("os.SEEK_SET")

   * "1" -- relative to the current buffer position ("os.SEEK_CUR")

   * "2" -- relative to the end of the file ("os.SEEK_END")

   *start*의 기본값은 파일 시작 부분에서 시작한다는 의미인 0입니다.
   *len*의 기본값은 파일 끝까지 잠그는 것을 의미하는 0입니다. *whence*
   의 기본값도 0입니다.

   인자 "fd", "cmd", "len", "start", "whence"로 감사 이벤트
   "fcntl.lockf"를 발생시킵니다.

예제 (모두 SVR4 호환 시스템에서):

   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)

첫 번째 예제에서 반환 값 변수 *rv*는 정숫값을 저장합니다; 두 번째 예제
에서는 "bytes" 객체를 저장합니다. *lockdata* 변수에 대한 구조체 배치는
시스템 종속적입니다 --- 그래서 "flock()" 호출을 사용하는 것이 더 좋을
수 있습니다.

더 보기:

  모듈 "os"
     If the locking flags "O_SHLOCK" and "O_EXLOCK" are present in the
     "os" module (on BSD only), the "os.open()" function provides an
     alternative to the "lockf()" and "flock()" functions.
