From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin-patches@cygwin.com
Subject: Re: [PATCH] Cygwin: getdtablesize: always return OPEN_MAX_MAX
Date: Thu, 28 Jan 2021 17:07:49 +0100 [thread overview]
Message-ID: <20210128160749.GB4393@calimero.vinschen.de> (raw)
In-Reply-To: <151a4199-92f2-43aa-dd91-5d86c2e1d3c6@cornell.edu>
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?
One problem is that there are some applications in the wild which run
loops up to either sysconf(_SC_OPEN_MAX) or OPEN_MAX to handle open
descriptors. tcsh is one of them. It may slow done tcsh quite a bit
if the loop runs to 3200 now every time.
Corinna
next prev parent reply other threads:[~2021-01-28 16:07 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 [this message]
2021-01-28 16:13 ` Corinna Vinschen
2021-01-28 22:28 ` Ken Brown
2021-01-29 19:23 ` Ken Brown
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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