First pass at fixing readdir by adding a getdents wrapper...

1 files changed, 114 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/common/getdents.c b/libc/sysdeps/linux/common/getdents.c
new file mode 100644
index 000000000..940532da2
--- /dev/null
+++ b/libc/sysdeps/linux/common/getdents.c
@@ -0,0 +1,114 @@
+/* Copyright (C) 1993, 95, 96, 97, 98, 99 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 Library General Public License as
+   published by the Free Software Foundation; either version 2 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If not,
+   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+   Boston, MA 02111-1307, USA.  */
+
+#include <stdlib.h>
+#include <errno.h>
+#include <dirent.h>
+#include <stddef.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/param.h>
+#include <sys/types.h>
+
+#include <sysdep.h>
+
+#include <linux/posix_types.h>
+
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+
+
+extern int _getdents __P ((int fd, char *buf, size_t nbytes));
+
+/* For Linux we need a special version of this file since the
+   definition of `struct dirent' is not the same for the kernel and
+   the libc.  There is one additional field which might be introduced
+   in the kernel structure in the future.
+   */
+#define dirent kernel_dirent
+#include <linux/dirent.h>
+#undef dirent
+
+
+#ifdef GETDENTS64
+# define __getdents __getdents64
+# define dirent dirent64
+#endif
+
+/* The problem here is that we cannot simply read the next NBYTES
+   bytes.  We need to take the additional field into account.  We use
+   some heuristic.  Assuming the directory contains names with 14
+   characters on average we can compute an estimated number of entries
+   which fit in the buffer.  Taking this number allows us to specify a
+   reasonable number of bytes to read.  If we should be wrong, we can
+   reset the file descriptor.  In practice the kernel is limiting the
+   amount of data returned much more then the reduced buffer size.  */
+ssize_t getdents (int fd, char *buf, size_t nbytes)
+{
+  off_t last_offset = 0;
+  size_t red_nbytes;
+  struct kernel_dirent *skdp, *kdp;
+  struct dirent *dp;
+  int retval;
+  const size_t size_diff = (offsetof (struct dirent, d_name)
+			    - offsetof (struct kernel_dirent, d_name));
+
+  red_nbytes = nbytes - ((nbytes / (offsetof (struct dirent, d_name) + 14))
+			 * size_diff);
+
+  dp = (struct dirent *) buf;
+  skdp = kdp = malloc (red_nbytes);
+
+  retval = _getdents(fd, (char *) kdp, red_nbytes);
+
+  if (retval == -1)
+    return -1;
+
+  while ((char *) kdp < (char *) skdp + retval)
+    {
+      const size_t alignment = __alignof__ (struct dirent);
+      /* Since kdp->d_reclen is already aligned for the kernel structure
+	 this may compute a value that is bigger than necessary.  */
+      size_t new_reclen = ((kdp->d_reclen + size_diff + alignment - 1)
+			   & ~(alignment - 1));
+      if ((char *) dp + new_reclen > buf + nbytes)
+	{
+	  /* Our heuristic failed.  We read too many entries.  Reset
+	     the stream.  `last_offset' contains the last known
+	     position.  If it is zero this is the first record we are
+	     reading.  In this case do a relative search.  */
+	  if (last_offset == 0)
+	    lseek (fd, -retval, SEEK_CUR);
+	  else
+	    lseek (fd, last_offset, SEEK_SET);
+	  break;
+	}
+
+      last_offset = kdp->d_off;
+      dp->d_ino = kdp->d_ino;
+      dp->d_off = kdp->d_off;
+      dp->d_reclen = new_reclen;
+      dp->d_type = DT_UNKNOWN;
+      memcpy (dp->d_name, kdp->d_name,
+	      kdp->d_reclen - offsetof (struct kernel_dirent, d_name));
+
+      dp = (struct dirent *) ((char *) dp + new_reclen);
+      kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
+    }
+
+  return (char *) dp - buf;
+}