summaryrefslogtreecommitdiff
path: root/sysdeps/unix/sysv/linux/getdents.c
blob: 836cbf39227f7007924b50f9ad35365acb4eee91 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
/* Copyright (C) 1993, 1995-2003, 2004, 2006 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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <alloca.h>
#include <assert.h>
#include <errno.h>
#include <dirent.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <sys/param.h>
#include <sys/types.h>

#include <sysdep.h>
#include <sys/syscall.h>
#include <bp-checks.h>

#include <linux/posix_types.h>

#include <kernel-features.h>

#ifdef __NR_getdents64
# ifndef __ASSUME_GETDENTS64_SYSCALL
#  ifndef __GETDENTS
/* The variable is shared between all *getdents* calls.  */
int __have_no_getdents64 attribute_hidden;
#  else
extern int __have_no_getdents64 attribute_hidden;
#  endif
#  define have_no_getdents64_defined 1
# endif
#endif
#ifndef have_no_getdents64_defined
# define __have_no_getdents64 0
#endif

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

/* 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 the kernel definition of `struct dirent' as of 2.1.20:  */

struct kernel_dirent
  {
    long int d_ino;
    __kernel_off_t d_off;
    unsigned short int d_reclen;
    char d_name[256];
  };

struct kernel_dirent64
  {
    uint64_t		d_ino;
    int64_t		d_off;
    unsigned short int	d_reclen;
    unsigned char	d_type;
    char		d_name[256];
  };

#ifndef __GETDENTS
# define __GETDENTS __getdents
#endif
#ifndef DIRENT_TYPE
# define DIRENT_TYPE struct dirent
#endif
#ifndef DIRENT_SET_DP_INO
# define DIRENT_SET_DP_INO(dp, value) (dp)->d_ino = (value)
#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
internal_function
__GETDENTS (int fd, char *buf, size_t nbytes)
{
  ssize_t retval;

#ifdef __ASSUME_GETDENTS32_D_TYPE
  if (sizeof (DIRENT_TYPE) == sizeof (struct dirent))
    {
      retval = INLINE_SYSCALL (getdents, 3, fd, CHECK_N(buf, nbytes), nbytes);

      /* The kernel added the d_type value after the name.  Change
	 this now.  */
      if (retval != -1)
	{
	  union
	  {
	    struct kernel_dirent k;
	    struct dirent u;
	  } *kbuf = (void *) buf;

	  while ((char *) kbuf < buf + retval)
	    {
	      char d_type = *((char *) kbuf + kbuf->k.d_reclen - 1);
	      memmove (kbuf->u.d_name, kbuf->k.d_name,
		       strlen (kbuf->k.d_name) + 1);
	      kbuf->u.d_type = d_type;

	      kbuf = (void *) ((char *) kbuf + kbuf->k.d_reclen);
	    }
	}

      return retval;
    }
#endif

  off64_t last_offset = -1;

#ifdef __NR_getdents64
  if (!__have_no_getdents64)
    {
# ifndef __ASSUME_GETDENTS64_SYSCALL
      int saved_errno = errno;
# endif
      union
      {
	struct kernel_dirent64 k;
	DIRENT_TYPE u;
	char b[1];
      } *kbuf = (void *) buf, *outp, *inp;
      size_t kbytes = nbytes;
      if (offsetof (DIRENT_TYPE, d_name)
	  < offsetof (struct kernel_dirent64, d_name)
	  && nbytes <= sizeof (DIRENT_TYPE))
	{
	  kbytes = nbytes + offsetof (struct kernel_dirent64, d_name)
		   - offsetof (DIRENT_TYPE, d_name);
	  kbuf = __alloca(kbytes);
	}
      retval = INLINE_SYSCALL (getdents64, 3, fd, CHECK_N(kbuf, kbytes),
			       kbytes);
# ifndef __ASSUME_GETDENTS64_SYSCALL
      if (retval != -1 || (errno != EINVAL && errno != ENOSYS))
# endif
	{
	  const size_t size_diff = (offsetof (struct kernel_dirent64, d_name)
				    - offsetof (DIRENT_TYPE, d_name));

	  /* Return the error if encountered.  */
	  if (retval == -1)
	    return -1;

	  /* If the structure returned by the kernel is identical to what we
	     need, don't do any conversions.  */
	  if (offsetof (DIRENT_TYPE, d_name)
	      == offsetof (struct kernel_dirent64, d_name)
	      && sizeof (outp->u.d_ino) == sizeof (inp->k.d_ino)
	      && sizeof (outp->u.d_off) == sizeof (inp->k.d_off))
	    return retval;

	  /* These two pointers might alias the same memory buffer.
	     Standard C requires that we always use the same type for them,
	     so we must use the union type.  */
	  inp = kbuf;
	  outp = (void *) buf;

	  while (&inp->b < &kbuf->b + retval)
	    {
	      const size_t alignment = __alignof__ (DIRENT_TYPE);
	      /* Since inp->k.d_reclen is already aligned for the kernel
		 structure this may compute a value that is bigger
		 than necessary.  */
	      size_t old_reclen = inp->k.d_reclen;
	      size_t new_reclen = ((old_reclen - size_diff + alignment - 1)
				  & ~(alignment - 1));

	      /* Copy the data out of the old structure into temporary space.
		 Then copy the name, which may overlap if BUF == KBUF.  */
	      const uint64_t d_ino = inp->k.d_ino;
	      const int64_t d_off = inp->k.d_off;
	      const uint8_t d_type = inp->k.d_type;

	      memmove (outp->u.d_name, inp->k.d_name,
		       old_reclen - offsetof (struct kernel_dirent64, d_name));

	      /* Now we have copied the data from INP and access only OUTP.  */

	      DIRENT_SET_DP_INO (&outp->u, d_ino);
	      outp->u.d_off = d_off;
	      if ((sizeof (outp->u.d_ino) != sizeof (inp->k.d_ino)
		   && outp->u.d_ino != d_ino)
		  || (sizeof (outp->u.d_off) != sizeof (inp->k.d_off)
		      && outp->u.d_off != d_off))
		{
		  /* Overflow.  If there was at least one entry
		     before this one, return them without error,
		     otherwise signal overflow.  */
		  if (last_offset != -1)
		    {
		      __lseek64 (fd, last_offset, SEEK_SET);
		      return outp->b - buf;
		    }
		  __set_errno (EOVERFLOW);
		  return -1;
		}

	      last_offset = d_off;
	      outp->u.d_reclen = new_reclen;
	      outp->u.d_type = d_type;

	      inp = (void *) inp + old_reclen;
	      outp = (void *) outp + new_reclen;
	    }

	  return outp->b - buf;
	}

# ifndef __ASSUME_GETDENTS64_SYSCALL
      __set_errno (saved_errno);
      __have_no_getdents64 = 1;
# endif
    }
#endif
  {
    size_t red_nbytes;
    struct kernel_dirent *skdp, *kdp;
    const size_t size_diff = (offsetof (DIRENT_TYPE, d_name)
			      - offsetof (struct kernel_dirent, d_name));

    red_nbytes = MIN (nbytes
		      - ((nbytes / (offsetof (DIRENT_TYPE, d_name) + 14))
			 * size_diff),
		      nbytes - size_diff);

    skdp = kdp = __alloca (red_nbytes);

    retval = INLINE_SYSCALL (getdents, 3, fd,
			     CHECK_N ((char *) kdp, red_nbytes), red_nbytes);

    if (retval == -1)
      return -1;

    DIRENT_TYPE *dp = (DIRENT_TYPE *) buf;
    while ((char *) kdp < (char *) skdp + retval)
      {
	const size_t alignment = __alignof__ (DIRENT_TYPE);
	/* 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.  */
	    assert (last_offset != -1);
	    __lseek64 (fd, last_offset, SEEK_SET);

	    if ((char *) dp == buf)
	      {
		/* The buffer the user passed in is too small to hold even
		   one entry.  */
		__set_errno (EINVAL);
		return -1;
	      }

	    break;
	  }

	last_offset = kdp->d_off;
	DIRENT_SET_DP_INO(dp, 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 = (DIRENT_TYPE *) ((char *) dp + new_reclen);
	kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
      }

    return (char *) dp - buf;
  }
}