[issue12556] Disable size checks in mmap.mmap()

[Charles-François Natali]

Charles-François Natali <neologix at free.fr> added the comment:

> By the way, I've checked mmap(2) manpage -- it looks like the C-version has
> nothing
> against mmaping 0-sized files, Why does Python's `mmap` still checks file
> size?

It doesn't check explicitely that the size is non-0, but rather that
the offset is is less than the file size.
Passing mmap(2) a 0 length doesn't make much sense anyway - for
example, Linux returns EINVAL:
http://lxr.free-electrons.com/source/mm/mmap.c?a=avr32#L979
"""
unsigned long do_mmap_pgoff(...)
[...]
        if (!len)
                 return -EINVAL;
"""

>> Do you have an example of a /proc entry with st_size == 0 that can be
>> mmapped
>> (mapping /proc/sys/debug/exception-trace fails with EACCESS)?
> Yes, I've ran into the issue, while trying to mmap /proc/xen/xsd_kva, which
> is an
> interface to XenBus [1]. Unfortunately, I'm not aware of any other cases.

That's what I thought, it's really uncommon: in that case, I'm
reluctant to making such a change, for the reason explained above.
Ross, Victor?

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<http://bugs.python.org/issue12556>
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