[newlib-cygwin] Cygwin: fhandler_base::open: allow to reopen file from handle

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c208ecd540c02773b0d25246e0fbaadcd416600a

commit c208ecd540c02773b0d25246e0fbaadcd416600a
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Sat Jan 5 21:49:16 2019 +0100

    Cygwin: fhandler_base::open: allow to reopen file from handle
    
    So far io_handle is NULL when calling fhandler_base::open to
    open or create a file.  Add a check for io_handle to allow
    priming the fhandler with a HANDLE value so we can reopen a
    file from a HANDLE on file systems supporting it.  This allows
    to open already deleted files for further action.  This will
    be used by open("/proc/PID/fd/DESCRIPTOR") scenarios.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/fhandler.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc
index f7e34c7..01afdb2 100644
--- a/winsup/cygwin/fhandler.cc
+++ b/winsup/cygwin/fhandler.cc
@@ -552,7 +552,12 @@ fhandler_base::open (int flags, mode_t mode)
 
   syscall_printf ("(%S, %y)", pc.get_nt_native_path (), flags);
 
-  pc.get_object_attr (attr, *sec_none_cloexec (flags));
+  /* Allow to reopen from handle.  This is utilized by
+     open ("/proc/PID/fd/DESCRIPTOR", ...); */
+  if (get_handle ())
+    pc.init_reopen_attr (attr, get_handle ());
+  else
+    pc.get_object_attr (attr, *sec_none_cloexec (flags));
 
   options = FILE_OPEN_FOR_BACKUP_INTENT;
   switch (query_open ())