sysdeps/unix/sysv/linux/getdents.c

   1 /* Copyright (C) 1993, 1995, 1996, 1997 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <dirent.h>
  20 #include <stddef.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <sys/types.h>
  24
  25 #include <linux/posix_types.h>
  26
  27 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
  28
  29
  30 extern int __getdents __P ((int fd, char *buf, size_t nbytes));
  31
  32 /* For Linux we need a special version of this file since the
  33    definition of `struct dirent' is not the same for the kernel and
  34    the libc.  There is one additional field which might be introduced
  35    in the kernel structure in the future.
  36
  37    He is the kernel definition of `struct dirent' as of 2.1.20:  */
  38
  39 struct kernel_dirent
  40   {
  41     long int d_ino;
  42     __kernel_off_t d_off;
  43     unsigned short int d_reclen;
  44     char d_name[256];
  45   };
  46
  47
  48 /* The problem here is that we cannot simply read the next NBYTES
  49    bytes.  We need to take the additional field into account.  We use
  50    some heuristic.  Assume the directory contains names with at least
  51    3 characters we can compute a maximum number of entries which fit
  52    in the buffer.  Taking this number allows us to specify a correct
  53    number of bytes to read.  If we should be wrong, we can reset the
  54    file descriptor.  */
  55 int __getdirentries __P ((int fd, char *buf, size_t nbytes, off_t *basep));
  56 int
  57 __getdirentries (fd, buf, nbytes, basep)
  58      int fd;
  59      char *buf;
  60      size_t nbytes;
  61      off_t *basep;
  62 {
  63   off_t base = __lseek (fd, (off_t) 0, SEEK_CUR);
  64   size_t red_nbytes;
  65   struct kernel_dirent *kdp;
  66   struct dirent *dp;
  67   int retval;
  68
  69   red_nbytes = nbytes - (nbytes / (offsetof (struct dirent, d_name) + 3));
  70
  71   dp = (struct dirent *) buf;
  72   kdp = (struct kernel_dirent *) (buf + (nbytes - red_nbytes));
  73
  74   retval = __getdents (fd, (char *) kdp, red_nbytes);
  75
  76   while ((char *) kdp < buf + (nbytes - red_nbytes) + retval)
  77     {
  78       dp->d_ino = kdp->d_ino;
  79       dp->d_off = kdp->d_off;
  80       dp->d_reclen = (kdp->d_reclen
  81                       + (offsetof (struct dirent, d_name)
  82                          - offsetof (struct kernel_dirent, d_name)));
  83       dp->d_type = DT_UNKNOWN;
  84       memmove (dp->d_name, kdp->d_name,
  85                kdp->d_reclen - offsetof (struct kernel_dirent, d_name));
  86
  87       dp = (struct dirent *) (((char *) dp) + dp->d_reclen);
  88       kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
  89
  90       if ((char *) dp >= (char *) kdp)
  91         {
  92           /* Our heuristic failed.  We read too many entries.  Reset
  93              the stream.  */
  94           off_t used = ((char *) kdp - (char *) buf) - (nbytes - red_nbytes);
  95           base = __lseek (fd, retval - used, SEEK_CUR);
  96         }
  97     }
  98
  99   if (basep)
 100     *basep = base;
 101
 102   return (char *) dp - (char *) buf;
 103 }
 104
 105 weak_alias (__getdirentries, getdirentries)