Bug report

Bug description:

The signature of mmap.flush is flush([offset[, size]]), so we should have the ability to call it with a_mmap_object.flush(4096).

But in current implementation, size's default value is the mmap object's size, so if the offset is non-zero, the total value of size and offset will be larger than the object's size, there is a check for this situation and if it happens, a ValueError will be raised.

So the size argument is required if user want to call it with with a non-zero offset, which is different to the document said.

There is a script to reproduce it:

import mmap
import os

f = open('test.tmp', 'wb+')
f.write(b'x' * mmap.PAGESIZE * 4)
f.flush()

m = mmap.mmap(f.fileno(), mmap.PAGESIZE * 4)

m.flush()
m.flush(mmap.PAGESIZE)
m.flush(mmap.PAGESIZE, mmap.PAGESIZE)

m.close()
f.close()
os.unlink('test.tmp')

Which will print:

Traceback (most recent call last):
  File "/home/xxxxx/Codes/cpython/test_flush_bug.py", line 11, in <module>
    m.flush(mmap.PAGESIZE)
    ~~~~~~~^^^^^^^^^^^^^^^
ValueError: flush values out of range

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-138092: Fix mmap.flush argument handling #138093