Assume O_DIRECTORY for opendir

This patch assumes O_DIRECTORY works as defined by POSIX on opendir
implementation (aligning with other glibc code, for instance pwd).  This
allows remove both the fallback code to handle system with missing or
broken O_DIRECTORY along with the Linux specific opendir.c which just
advertise the working flag.

Checked on aarch64-linux-gnu, x86_64-linux-gnu, i686-linux-gnu,
sparcv9-linux-gnu, sparc64-linux-gnu, powerpc-linux-gnu, and
powerpc64le-linux-gnu.

	* sysdeps/posix/opendir.c (o_directory_works, tryopen_o_directory):
	Remove definitions.
	(opendir_oflags): Use O_DIRECTORY regardless.
	(__opendir, __opendirat): Remove need_isdir_precheck usage.
	* sysdeps/unix/sysv/linux/opendir.c: Remove file.

2 files changed, 5 insertions, 123 deletions

diff --git a/sysdeps/posix/opendir.c b/sysdeps/posix/opendir.c
index d925804e89..dea23b2ff5 100644
--- a/sysdeps/posix/opendir.c
+++ b/sysdeps/posix/opendir.c
@@ -15,24 +15,13 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <assert.h>
-#include <errno.h>
-#include <limits.h>
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdlib.h>
 #include <dirent.h>
 #include <fcntl.h>
-#include <sys/param.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <unistd.h>
-#include <stdio.h>
-#include <string.h>
-
-#include <dirstream.h>
+#include <errno.h>
+#include <stdio.h>	/* For BUFSIZ.  */
+#include <sys/param.h>	/* For MIN and MAX.  */
+
 #include <not-cancel.h>
-#include <kernel-features.h>
 
 /* The st_blksize value of the directory is used as a hint for the
    size of the buffer which receives struct dirent values from the
@@ -40,49 +29,8 @@
    file system provides a bogus value.  */
 #define MAX_DIR_BUFFER_SIZE 1048576U
 
-/* opendir() must not accidentally open something other than a directory.
-   Some OS's have kernel support for that, some don't.  In the worst
-   case we have to stat() before the open() AND fstat() after.
-
-   We have to test at runtime for kernel support since libc may have
-   been compiled with different headers to the kernel it's running on.
-   This test can't be done reliably in the general case.  We'll use
-   /dev/null, which if it's not a device lots of stuff will break, as
-   a guinea pig.  It may be missing in chroot environments, so we
-   make sure to fail safe. */
-#ifdef O_DIRECTORY
-# ifdef O_DIRECTORY_WORKS
-#  define o_directory_works 1
-#  define tryopen_o_directory() while (1) /* This must not be called.  */
-# else
-static int o_directory_works;
-
-static void
-tryopen_o_directory (void)
-{
-  int serrno = errno;
-  int x = __open_nocancel ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
-
-  if (x >= 0)
-    {
-      __close_nocancel_nostatus (x);
-      o_directory_works = -1;
-    }
-  else if (errno != ENOTDIR)
-    o_directory_works = -1;
-  else
-    o_directory_works = 1;
-
-  __set_errno (serrno);
-}
-# endif
-# define EXTRA_FLAGS O_DIRECTORY
-#else
-# define EXTRA_FLAGS 0
-#endif
-
 enum {
-  opendir_oflags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE|O_CLOEXEC
+  opendir_oflags = O_RDONLY|O_NDELAY|O_DIRECTORY|O_LARGEFILE|O_CLOEXEC
 };
 
 static bool
@@ -98,21 +46,6 @@ invalid_name (const char *name)
   return false;
 }
 
-
-static bool
-need_isdir_precheck (void)
-{
-#ifdef O_DIRECTORY
-  /* Test whether O_DIRECTORY works.  */
-  if (o_directory_works == 0)
-    tryopen_o_directory ();
-
-  /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
-  return o_directory_works < 0;
-#endif
-  return true;
-}
-
 static DIR *
 opendir_tail (int fd)
 {
@@ -144,22 +77,6 @@ __opendirat (int dfd, const char *name)
   if (__glibc_unlikely (invalid_name (name)))
     return NULL;
 
-  if (need_isdir_precheck ())
-    {
-      /* We first have to check whether the name is for a directory.  We
-	 cannot do this after the open() call since the open/close operation
-	 performed on, say, a tape device might have undesirable effects.  */
-      struct stat64 statbuf;
-      if (__glibc_unlikely (__fxstatat64 (_STAT_VER, dfd, name,
-					  &statbuf, 0) < 0))
-	return NULL;
-      if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
-	{
-	  __set_errno (ENOTDIR);
-	  return NULL;
-	}
-    }
-
   return opendir_tail (__openat_nocancel (dfd, name, opendir_oflags));
 }
 #endif
@@ -172,21 +89,6 @@ __opendir (const char *name)
   if (__glibc_unlikely (invalid_name (name)))
     return NULL;
 
-  if (need_isdir_precheck ())
-    {
-      /* We first have to check whether the name is for a directory.  We
-	 cannot do this after the open() call since the open/close operation
-	 performed on, say, a tape device might have undesirable effects.  */
-      struct stat64 statbuf;
-      if (__glibc_unlikely (__xstat64 (_STAT_VER, name, &statbuf) < 0))
-	return NULL;
-      if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
-	{
-	  __set_errno (ENOTDIR);
-	  return NULL;
-	}
-    }
-
   return opendir_tail (__open_nocancel (name, opendir_oflags));
 }
 weak_alias (__opendir, opendir)
diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c
deleted file mode 100644
index 2677253620..0000000000
--- a/sysdeps/unix/sysv/linux/opendir.c
+++ /dev/null
@@ -1,20 +0,0 @@
-/* Copyright (C) 2000-2018 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-#define O_DIRECTORY_WORKS	1
-
-#include <sysdeps/posix/opendir.c>