gh-95672 skip fcntl when pipesize is smaller than pagesize

Doc/library/test.rst

@@ -536,6 +536,11 @@ The :mod:`test.support` module defines the following functions:
    :func:`doctest.testmod`.
 
 
+.. function:: get_pagesize()
+
+   Get size of a page in bytes.
+
+
 .. function:: setswitchinterval(interval)
 
    Set the :func:`sys.setswitchinterval` to the given *interval*.  Defines

Lib/test/support/__init__.py

@@ -51,6 +51,8 @@
     # sys
     "is_jython", "is_android", "is_emscripten", "is_wasi",
     "check_impl_detail", "unix_shell", "setswitchinterval",
+    # os
+    "get_pagesize",
     # network
     "open_urlresource",
     # processes
@@ -1892,6 +1894,16 @@ def setswitchinterval(interval):
             interval = minimum_interval
     return sys.setswitchinterval(interval)
 
+def get_pagesize():
+    """Get size of a page in bytes."""
+    try:
+        page_size = os.sysconf('SC_PAGESIZE')
+    except (ValueError, AttributeError):
+        try:
+            page_size = os.sysconf('SC_PAGE_SIZE')
+        except (ValueError, AttributeError):
+            page_size = 4096
+    return page_size
 
 @contextlib.contextmanager
 def disable_faulthandler():

Lib/test/test_fcntl.py

@@ -6,6 +6,7 @@
 import struct
 import sys
 import unittest
+from test import support
 from test.support import verbose, cpython_only
 from test.support.import_helper import import_module
 from test.support.os_helper import TESTFN, unlink
@@ -201,7 +202,8 @@ def test_fcntl_f_pipesize(self):
             # Get the default pipesize with F_GETPIPE_SZ
             pipesize_default = fcntl.fcntl(test_pipe_w, fcntl.F_GETPIPE_SZ)
             pipesize = pipesize_default // 2  # A new value to detect change.
-            if pipesize < 512:  # the POSIX minimum
+            pagesize_default = support.get_pagesize()
+            if pipesize < pagesize_default:  # the POSIX minimum
                 raise unittest.SkipTest(
                     'default pipesize too small to perform test.')
             fcntl.fcntl(test_pipe_w, fcntl.F_SETPIPE_SZ, pipesize)

Lib/test/test_subprocess.py

@@ -717,7 +717,8 @@ def test_pipesizes(self):
             os.close(test_pipe_r)
             os.close(test_pipe_w)
         pipesize = pipesize_default // 2
-        if pipesize < 512:  # the POSIX minimum
+        pagesize_default = support.get_pagesize()
+        if pipesize < pagesize_default:  # the POSIX minimum
             raise unittest.SkipTest(
                 'default pipesize too small to perform test.')
         p = subprocess.Popen(