From: Ken Brown <kbrown@cornell.edu>
To: cygwin-patches@cygwin.com
Subject: Re: [PATCH] Cygwin: getdtablesize: always return OPEN_MAX_MAX
Date: Fri, 29 Jan 2021 14:23:21 -0500 [thread overview]
Message-ID: <36a6753f-9aaa-f2ce-f71f-40385b3214c3@cornell.edu> (raw)
In-Reply-To: <a4cd3c3f-d217-026a-3cce-b29187ecd1e9@cornell.edu>
On 1/28/2021 5:28 PM, Ken Brown via Cygwin-patches wrote:
> On 1/28/2021 11:13 AM, Corinna Vinschen via Cygwin-patches wrote:
>> On Jan 28 17:07, Corinna Vinschen via Cygwin-patches wrote:
>>> On Jan 28 08:42, Ken Brown via Cygwin-patches wrote:
>>>> On 1/28/2021 5:20 AM, Corinna Vinschen via Cygwin-patches wrote:
>>>>> On Jan 27 21:51, Ken Brown via Cygwin-patches wrote:
>>>>>> According to the Linux man page for getdtablesize(3), the latter is
>>>>>> supposed to return "the maximum number of files a process can have
>>>>>> open, one more than the largest possible value for a file descriptor."
>>>>>> The constant OPEN_MAX_MAX is the only limit enforced by Cygwin, so we
>>>>>> now return that.
>>>>>>
>>>>>> Previously getdtablesize returned the current size of cygheap->fdtab,
>>>>>> Cygwin's internal file descriptor table. But this is a dynamically
>>>>>> growing table, and its current size does not reflect an actual limit
>>>>>> on the number of open files.
>>>>>>
>>>>>> With this change, gnulib now reports that getdtablesize and
>>>>>> fcntl(F_DUPFD) work on Cygwin. Packages like GNU tar that use the
>>>>>> corresponding gnulib modules will no longer use gnulib replacements on
>>>>>> Cygwin.
>>>>>> ---
>>>>>> winsup/cygwin/syscalls.cc | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
>>>>>> index 5da05b18a..1f16d54b9 100644
>>>>>> --- a/winsup/cygwin/syscalls.cc
>>>>>> +++ b/winsup/cygwin/syscalls.cc
>>>>>> @@ -2887,7 +2887,7 @@ setdtablesize (int size)
>>>>>> extern "C" int
>>>>>> getdtablesize ()
>>>>>> {
>>>>>> - return cygheap->fdtab.size;
>>>>>> + return OPEN_MAX_MAX;
>>>>>> }
>>>>>
>>>>> getdtablesize is used internally, too. After this change, the values
>>>>> returned by sysconf and getrlimit should be revisited as well.
>>>>
>>>> They will now return OPEN_MAX_MAX, as I think they should. The only
>>>> question in my mind is whether to simplify the code by removing the calls to
>>>> getdtablesize, something like this (untested):
>>>
>>> But then again, what happens with OPEN_MAX in limits.h? Linux removed
>>> it entirely. Given we have such a limit and it's not flexible as on
>>> Linux, should we go ahead, drop OPEN_MAX_MAX entirely and define
>>> OPEN_MAX as 3200?
>>
>> ...ideally by adding a file include/cygwin/limits.h included by
>> include/limits.h, which defines __OPEN_MAX et al, as required.
>
> I'm not completely sure I follow. Do you mean include/cygwin/limits.h should
> contain
>
> #define __OPEN_MAX 3200
>
> and include/limits.h should contain
>
> #define OPEN_MAX __OPEN_MAX ?
>
> For the sake of my education, could you explain the reason for this?
Trying to answer my own question, I guess the idea is to hide implementation
details from viewers of limits.h. Is that right? I took a stab at this and am
about to send a patchset. I'm not sure whether I made a reasonable choice of
"et al" in "__OPEN_MAX et al".
Ken
next prev parent reply other threads:[~2021-01-29 19:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 2:51 Ken Brown
2021-01-28 10:20 ` Corinna Vinschen
2021-01-28 13:42 ` Ken Brown
2021-01-28 16:07 ` Corinna Vinschen
2021-01-28 16:13 ` Corinna Vinschen
2021-01-28 22:28 ` Ken Brown
2021-01-29 19:23 ` Ken Brown [this message]
2021-02-01 9:42 ` Corinna Vinschen
2021-01-28 20:33 ` Ken Brown
2021-02-01 9:50 ` Corinna Vinschen
2021-02-01 10:46 ` Corinna Vinschen
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