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/* 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 <bits/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. Here is a copy of the kernel
struct dirent...
*/
struct kernel_dirent {
long d_ino;
__kernel_off_t d_off;
unsigned short d_reclen;
char d_name[256]; /* We must not include limits.h! */
};
#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;
}
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