Cygwin: introduce fhandler_process_fd and add stat(2) handling

move special fd symlink code into own fhandler_process_fd class
to simplify further additions to /proc/PID/fd/DESCRIPTOR symlink
handling.

Add a method to handle stat(2) on such a proc fd symlink by handle.
This allows correct reply from stat(2) if the target file has been
deleted.  This eventually fixes `awk -f /dev/fd/3 3<<eof'.

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

winsup/cygwin/fhandler_process_fd.cc

@@ -0,0 +1,153 @@
+/* fhandler_process_fd.cc: fhandler for /proc/<pid>/fd/<desc> operations
+
+This file is part of Cygwin.
+
+This software is a copyrighted work licensed under the terms of the
+Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+details. */
+
+#include "winsup.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/cygwin.h>
+#include "cygerrno.h"
+#include "security.h"
+#include "path.h"
+#include "fhandler.h"
+#include "fhandler_virtual.h"
+#include "pinfo.h"
+#include "shared_info.h"
+#include "dtable.h"
+#include "cygheap.h"
+#include "ntdll.h"
+#include "cygtls.h"
+#include "mount.h"
+#include "tls_pbuf.h"
+#include <sys/sysmacros.h>
+#include <sys/param.h>
+#include <ctype.h>
+
+
+fhandler_base *
+fhandler_process_fd::fetch_fh (HANDLE &out_hdl)
+{
+  const char *path;
+  char *e;
+  int fd;
+  HANDLE proc;
+  HANDLE hdl = NULL;
+  path_conv pc;
+
+  path = get_name () + proc_len + 1;
+  pid = strtoul (path, &e, 10);
+  path = e + 4;
+  fd = strtoul (path, &e, 10);
+
+  out_hdl = NULL;
+  if (pid == myself->pid)
+    {
+      cygheap_fdget cfd (fd, true);
+      if (cfd < 0)
+	return NULL;
+      proc = GetCurrentProcess ();
+      pc << cfd->pc;
+      hdl = cfd->get_handle ();
+    }
+  else
+    {
+      pinfo p (pid);
+      if (!p)
+	{
+	  set_errno (ENOENT);
+	  return NULL;
+	}
+      proc = OpenProcess (PROCESS_DUP_HANDLE, false, p->dwProcessId);
+      if (!proc)
+	{
+	  __seterrno ();
+	  return NULL;
+	}
+      size_t size;
+      void *buf = p->file_pathconv (fd, size);
+      if (size == 0)
+	{
+	  set_errno (EPERM);
+	  CloseHandle (proc);
+	  return NULL;
+	}
+      hdl = pc.deserialize (buf);
+    }
+  BOOL ret = DuplicateHandle (proc, hdl, GetCurrentProcess (), &hdl,
+			 0, FALSE, DUPLICATE_SAME_ACCESS);
+  if (proc != GetCurrentProcess ())
+    CloseHandle (proc);
+  if (!ret)
+    {
+      __seterrno ();
+      CloseHandle (hdl);
+      return NULL;
+    }
+  fhandler_base *fh = build_fh_pc (pc);
+  if (!fh)
+    {
+      CloseHandle (hdl);
+      return NULL;
+    }
+  out_hdl = hdl;
+  return fh;
+}
+
+fhandler_base *
+fhandler_process_fd::fd_reopen (int flags)
+{
+  fhandler_base *fh;
+  HANDLE hdl;
+
+  fh = fetch_fh (hdl);
+  if (!fh)
+    return NULL;
+  fh->set_io_handle (hdl);
+  int ret = fh->open_with_arch (flags, 0);
+  CloseHandle (hdl);
+  if (!ret)
+    {
+      delete fh;
+      fh = NULL;
+    }
+  return fh;
+}
+
+int __reg2
+fhandler_process_fd::fstat (struct stat *statbuf)
+{
+  if (!pc.follow_fd_symlink ())
+    return fhandler_process::fstat (statbuf);
+
+  fhandler_base *fh;
+  HANDLE hdl;
+
+  fh = fetch_fh (hdl);
+  if (!fh)
+    return -1;
+  fh->set_io_handle (hdl);
+  int ret = fh->fstat (statbuf);
+  CloseHandle (hdl);
+  delete fh;
+  return ret;
+}
+
+int
+fhandler_process_fd::link (const char *newpath)
+{
+  fhandler_base *fh;
+  HANDLE hdl;
+
+  fh = fetch_fh (hdl);
+  if (!fh)
+    return -1;
+  fh->set_io_handle (hdl);
+  int ret = fh->link (newpath);
+  CloseHandle (hdl);
+  delete fh;
+  return ret;
+}