[newlib-cygwin] Implement fhandler_dev_null::write to workaround a problem with NUL

[Corinna Vinschen <corinna at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=dd757cc43a710204046919da2cecf5f3b72ba33c

commit dd757cc43a710204046919da2cecf5f3b72ba33c
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Sun Mar 12 12:17:43 2017 +0100

    Implement fhandler_dev_null::write to workaround a problem with NUL
    
    Windows NUL device returns only the lower 32 bit of the number of
    bytes written.  Implement a fake write function to ignore the underlying
    NUL device.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/fhandler.cc | 9 +++++++++
 winsup/cygwin/fhandler.h  | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc
index af33480..d719b7c 100644
--- a/winsup/cygwin/fhandler.cc
+++ b/winsup/cygwin/fhandler.cc
@@ -1529,6 +1529,15 @@ fhandler_dev_null::fhandler_dev_null () :
 {
 }
 
+ssize_t __stdcall
+fhandler_dev_null::write (const void *ptr, size_t len)
+{
+  /* Shortcut.  This also fixes a problem with the NUL device on 64 bit:
+     If you write > 4 GB in a single attempt, the bytes written returned
+     from by is numBytes & 0xffffffff. */
+  return len;
+}
+
 void
 fhandler_base::set_no_inheritance (HANDLE &h, bool not_inheriting)
 {
diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index 14f7680..153e384 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -1682,6 +1682,8 @@ class fhandler_dev_null: public fhandler_base
     copyto (fh);
     return fh;
   }
+
+  ssize_t __stdcall write (const void *ptr, size_t len);
 };
 
 class fhandler_dev_zero: public fhandler_base