[PATCH] Cygwin: getdtablesize: always return OPEN_MAX_MAX

Ken Brown kbrown@cornell.edu
Thu Jan 28 02:51:50 GMT 2021

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
 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;
 extern "C" int

More information about the Cygwin-patches mailing list