linux: Move posix dir implementations to Linux

This generic implementation already expects a getdents API which
is Linux specific.  It also allows simplify it by assuming
_DIRENT_HAVE_D_RECLEN and _DIRENT_HAVE_D_OFF support.

The readdir are also expanded on each required implementation,
futher fixes and improvements will make parametrize the
implementation more complex.

Checked on x86_64-linux-gnu, i686-linux-gnu, and with a build
for all affected ABIs.

1 files changed, 148 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c
new file mode 100644
index 0000000000..e89e09bfc7
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/opendir.c
@@ -0,0 +1,148 @@
+/* Copyright (C) 1991-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdio.h>	/* For BUFSIZ.  */
+#include <sys/param.h>	/* For MIN and MAX.  */
+
+#include <not-cancel.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
+   kernel.  st_blksize is limited to MAX_DIR_BUFFER_SIZE, in case the
+   file system provides a bogus value.  */
+#define MAX_DIR_BUFFER_SIZE 1048576U
+
+enum {
+  opendir_oflags = O_RDONLY|O_NDELAY|O_DIRECTORY|O_LARGEFILE|O_CLOEXEC
+};
+
+static bool
+invalid_name (const char *name)
+{
+  if (__glibc_unlikely (name[0] == '\0'))
+    {
+      /* POSIX.1-1990 says an empty name gets ENOENT;
+	 but `open' might like it fine.  */
+      __set_errno (ENOENT);
+      return true;
+    }
+  return false;
+}
+
+static DIR *
+opendir_tail (int fd)
+{
+  if (__glibc_unlikely (fd < 0))
+    return NULL;
+
+  /* Now make sure this really is a directory and nothing changed since the
+     `stat' call.  The S_ISDIR check is superfluous if O_DIRECTORY works,
+     but it's cheap and we need the stat call for st_blksize anyway.  */
+  struct stat64 statbuf;
+  if (__glibc_unlikely (__fstat64 (fd, &statbuf) < 0))
+    goto lose;
+  if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode)))
+    {
+      __set_errno (ENOTDIR);
+    lose:
+      __close_nocancel_nostatus (fd);
+      return NULL;
+    }
+
+  return __alloc_dir (fd, true, 0, &statbuf);
+}
+
+
+#if IS_IN (libc)
+DIR *
+__opendirat (int dfd, const char *name)
+{
+  if (__glibc_unlikely (invalid_name (name)))
+    return NULL;
+
+  return opendir_tail (__openat_nocancel (dfd, name, opendir_oflags));
+}
+#endif
+
+
+/* Open a directory stream on NAME.  */
+DIR *
+__opendir (const char *name)
+{
+  if (__glibc_unlikely (invalid_name (name)))
+    return NULL;
+
+  return opendir_tail (__open_nocancel (name, opendir_oflags));
+}
+weak_alias (__opendir, opendir)
+
+DIR *
+__alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
+{
+  /* We have to set the close-on-exit flag if the user provided the
+     file descriptor.  */
+  if (!close_fd
+      && __glibc_unlikely (__fcntl64_nocancel (fd, F_SETFD, FD_CLOEXEC) < 0))
+	goto lose;
+
+  const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
+				     ? sizeof (struct dirent64) : 4 * BUFSIZ);
+  const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
+				   ? sizeof (struct dirent64) : BUFSIZ);
+  size_t allocation = default_allocation;
+#ifdef _STATBUF_ST_BLKSIZE
+  /* Increase allocation if requested, but not if the value appears to
+     be bogus.  */
+  if (statp != NULL)
+    allocation = MIN (MAX ((size_t) statp->st_blksize, default_allocation),
+		      MAX_DIR_BUFFER_SIZE);
+#endif
+
+  DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
+  if (dirp == NULL)
+    {
+      allocation = small_allocation;
+      dirp = (DIR *) malloc (sizeof (DIR) + allocation);
+
+      if (dirp == NULL)
+      lose:
+	{
+	  if (close_fd)
+	    {
+	      int save_errno = errno;
+	      __close_nocancel_nostatus (fd);
+	      __set_errno (save_errno);
+	    }
+	  return NULL;
+	}
+    }
+
+  dirp->fd = fd;
+#if IS_IN (libc)
+  __libc_lock_init (dirp->lock);
+#endif
+  dirp->allocation = allocation;
+  dirp->size = 0;
+  dirp->offset = 0;
+  dirp->filepos = 0;
+  dirp->errcode = 0;
+
+  return dirp;
+}