Cygwin: proc fd: fix handling of pipes, sockets, etc

The symlink target of /proc/PID/fd files pointing to pipes and
sockets are just artificial filenames referencing the object using
some internal number.  The pipe open code expects a path specifying
process pid and the internal number so it access the right process
and pipe.

- Set the posix path of the pipe to the simple pipe name only,
  as it shows up in /proc/PID/fd.  A /proc/self prefix is just
  as wrong as a /dev/fd prefix.

- Revert thinko in fhandler_pipe::open expecting the name as
  /proc/self/fd/...  In fact this should never happen.

- Fix up the path before re-opening the pipe instead.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_process_fd.cc

@@ -13,6 +13,7 @@ details. */
 #include "pinfo.h"
 #include "dtable.h"
 #include "cygheap.h"
+#include "tls_pbuf.h"
 
 fhandler_base *
 fhandler_process_fd::fetch_fh (HANDLE &out_hdl, uint32_t flags)
@@ -86,6 +87,16 @@ fhandler_process_fd::fetch_fh (HANDLE &out_hdl, uint32_t flags)
       CloseHandle (hdl);
       return NULL;
     }
+  /* relative path?  This happens for special types like pipes and sockets. */
+  if (*pc.get_posix () != '/')
+    {
+      tmp_pathbuf tp;
+      char *fullpath = tp.c_get ();
+
+      stpcpy (stpncpy (fullpath, get_name (), path - get_name ()),
+	      pc.get_posix ());
+      pc.set_posix (fullpath);
+    }
   fhandler_base *fh = build_fh_pc (pc);
   if (!fh)
     {