Get maximum pipe size. See F_GETPIPE_SZ in fcntl(2).

get_max_pipe.py

# -*- coding: utf-8 -*-
"""
  Get maximum pipe size (F_GETPIPE_SZ)
  See http://man7.org/linux/man-pages/man2/fcntl.2.html

"""
import fcntl
import os


F_GETPIPE_SZ = 1032  # Linux 2.6.35+

def get_max_pipe():
    """Get the maximum pipe buffer size or None."""
    r, w = os.pipe()
    try:
        return fcntl.fcntl(w, F_GETPIPE_SZ)
    except OSError:
        return None
    finally:
        os.closerange(r, w)

Thanks for posting this. The return value of the call to fcntl represents the capacity of the pipe, not the maximum size.

       F_GETPIPE_SZ (void; since Linux 2.6.35)
              Return (as the function result) the capacity of the pipe
              referred to by fd.

The maximum size can be learned by reading /proc/sys/fs/pipe-max-size

       F_SETPIPE_SZ (int; since Linux 2.6.35)
              Change the capacity of the pipe referred to by fd to be at
              least arg bytes.  An unprivileged process can adjust the pipe
              capacity to any value between the system page size and the
              limit defined in /proc/sys/fs/pipe-max-size (see proc(5)).
              Attempts to set the pipe capacity below the page size are
              silently rounded up to the page size.  Attempts by an unprivi‐
              leged process to set the pipe capacity above the limit in
              /proc/sys/fs/pipe-max-size yield the error EPERM; a privileged
              process (CAP_SYS_RESOURCE) can override the limit.

from http://man7.org/linux/man-pages/man2/fcntl.2.html