Corinna Vinschen wrote:
> Hi Christian,
>
> On Jan 15 09:56, Christian Franke wrote:
>> Christian Franke wrote:
>>> Jon Turney wrote:
>>>> On 14/01/2024 16:07, Christian Franke wrote:
>>>>> Recently I learned about the existence and usefulness of close_range():
>>>>> https://github.com/smartmontools/smartmontools/issues/235
>>>>>
>>>>> https://man.freebsd.org/cgi/man.cgi?query=close_range&sektion=2
>>>>> https://man7.org/linux/man-pages/man2/close_range.2.html
>>>>>
>>>>> Note that the above Linux man page is not fully correct. The
>>>>> include file "linux/close_range.h" exists, but provides only the
>>>>> defines. It is sufficient to include "unistd.h" as on FreeBSD.
>>>>>
>>>>> The attached patch adds this to Cygwin. It does not implement
>>>>> the Linux-specific CLOSE_RANGE_UNSHARE as I have no idea how to
>>>>> do this :-)
>>>> This API should also be mentioned in the
>>>> "System interfaces compatible with GNU or Linux extensions" section
>>>> of doc/posix.xml
>>>>
>>>>
>>> Thanks for the info. I used the recent "Cygwin: introduce fallocate(2)"
>>> patch as a blueprint for which other files should be changed (fallocate
>>> is also missing in the posix.xml file).
>>>
>>> I will provide a new patch soon which also fixes an unlikely but
>>> possible corner case: Pass a value larger than MAX_INT as lower limit.
>>>
>> Attached. I also decided to simply ignore CLOSE_RANGE_UNSHARE for now.
> After reading up on this issue, I think we should not ignore
> CLOSE_RANGE_UNSHARE, but quite explicitely not implement it as a valid
> flag.
>
> The whole idea behind CLOSE_RANGE_UNSHARE depends on the way the Linux
> kernel creates threads and (forked) processes and the fact that it has a
> wide range of ways to share parts of the execution context between
> parent and child process/thread.
>
> So on Linux, a process/thread can actually decide if they share or not
> share the descriptor table with the created process/thread.  That's
> what the CLONE_FILES flag to clone(2) and unshare(2) manage.
>
> However, just as in FreeBSD, there's no such thing in Cygwin.  Threads
> always share descriptors, processes never share file desriptors.
>
> The bottom line is, I think the decision of the FreeBSD developer not to
> expose the CLOSE_RANGE_UNSHARE flag at all, was the right decision.
>
> We should not claim that we even remotely have a way of doing this
> the Linux way.
>
> Does that make sense?

Yes - new patch attached.