[newlib-cygwin] Cygwin: getdtablesize: always return OPEN_MAX_MAX

[Ken Brown]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=3d256e22e22d435d13cfecf39c15338cfbd6f587

commit 3d256e22e22d435d13cfecf39c15338cfbd6f587
Author: Ken Brown <kbrown@cornell.edu>
Date:   Wed Jan 27 20:06:22 2021 -0500

    Cygwin: getdtablesize: always return OPEN_MAX_MAX
    
    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.

Diff:
---
 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 82ddad46d..d293ff2c0 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;
 }
 
 extern "C" int