gh-132742: Refactor fcntl.fcntl() and fcntl.ioctl() (GH-132768)

* Support arbitrary bytes-like objects, not only bytes, in fcntl().
* The fcntl() buffer argument is now null-terminated.
* Automatically retry an ioctl() system calls failing with EINTR.
* Release the GIL for an ioctl() system call even for large bytes-like object.
* Do not silence arbitrary errors whet try to get a buffer.
* Optimize argument parsing, check the argument type before trying to get
  a buffer or convert it to integer.
* Fix some error messages.

Author: serhiy-storchaka

Doc/library/fcntl.rst

@@ -89,14 +89,14 @@ The module defines the following functions:
    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, a
-   :class:`bytes` object, or a string.
+   :term:`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.
 
    When *arg* is an integer, the function returns the integer
    return value of the C :c:func:`fcntl` call.
 
-   When the argument is bytes, it represents a binary structure,
+   When the argument is bytes-like object, it represents a binary structure,
    for example, created by :func:`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
@@ -117,6 +117,10 @@ The module defines the following functions:
 
    .. audit-event:: fcntl.fcntl fd,cmd,arg fcntl.fcntl
 
+   .. versionchanged:: next
+      Add support of arbitrary :term:`bytes-like objects <bytes-like object>`,
+      not only :class:`bytes`.
+
 
 .. function:: ioctl(fd, request, arg=0, mutate_flag=True, /)
 
@@ -173,6 +177,9 @@ The module defines the following functions:
 
    .. audit-event:: fcntl.ioctl fd,request,arg fcntl.ioctl
 
+   .. versionchanged:: next
+      The GIL is always released during a system call.
+      System calls failing with EINTR are automatically retried.
 
 .. function:: flock(fd, operation, /)
 

Misc/NEWS.d/next/Library/2025-04-23-14-50-45.gh-issue-132742.PB6B7F.rst

@@ -0,0 +1,4 @@
+:func:`fcntl.fcntl` now supports arbitrary :term:`bytes-like objects
+<bytes-like object>`, not only :class:`bytes`. :func:`fcntl.ioctl` now
+automatically retries system calls failing with EINTR and releases the GIL
+during a system call even for large bytes-like object.