summaryrefslogtreecommitdiffstats
path: root/lib/fchdir.c
blob: 880b137ec66ce4b5d4a76401d914ebe4bd5ceb0c (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
/* fchdir replacement.
   Copyright (C) 2006-2023 Free Software Foundation, Inc.

   This file 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 3 of the
   License, or (at your option) any later version.

   This file 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include <unistd.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "assure.h"
#include "filename.h"
#include "filenamecat.h"

#ifndef REPLACE_OPEN_DIRECTORY
# define REPLACE_OPEN_DIRECTORY 0
#endif

/* This replacement assumes that a directory is not renamed while opened
   through a file descriptor.

   FIXME: On mingw, this would be possible to enforce if we were to
   also open a HANDLE to each directory currently visited by a file
   descriptor, since mingw refuses to rename any in-use file system
   object.  */

/* Array of file descriptors opened.  If REPLACE_OPEN_DIRECTORY or if it points
   to a directory, it stores info about this directory.  */
typedef struct
{
  char *name;       /* Absolute name of the directory, or NULL.  */
} dir_info_t;
static dir_info_t *dirs;
static size_t dirs_allocated;

/* Try to ensure dirs has enough room for a slot at index fd; free any
   contents already in that slot.  Return false and set errno to
   ENOMEM on allocation failure.  */
static bool
ensure_dirs_slot (size_t fd)
{
  if (fd < dirs_allocated)
    free (dirs[fd].name);
  else
    {
      size_t new_allocated;
      dir_info_t *new_dirs;

      new_allocated = 2 * dirs_allocated + 1;
      if (new_allocated <= fd)
        new_allocated = fd + 1;
      new_dirs =
        (dirs != NULL
         ? (dir_info_t *) realloc (dirs, new_allocated * sizeof *dirs)
         : (dir_info_t *) malloc (new_allocated * sizeof *dirs));
      if (new_dirs == NULL)
        return false;
      memset (new_dirs + dirs_allocated, 0,
              (new_allocated - dirs_allocated) * sizeof *dirs);
      dirs = new_dirs;
      dirs_allocated = new_allocated;
    }
  return true;
}

/* Return an absolute name of DIR in malloc'd storage.
   Upon failure, return NULL with errno set.  */
static char *
get_name (char const *dir)
{
  char *cwd;
  char *result;

  if (IS_ABSOLUTE_FILE_NAME (dir))
    return strdup (dir);

  /* We often encounter "."; treat it as a special case.  */
  cwd = getcwd (NULL, 0);
  if (!cwd || (dir[0] == '.' && dir[1] == '\0'))
    return cwd;

  result = mfile_name_concat (cwd, dir, NULL);
  free (cwd);
  return result;
}

/* Hook into the gnulib replacements for open() and close() to keep track
   of the open file descriptors.  */

/* Close FD, cleaning up any fd to name mapping if fd was visiting a
   directory.  */
void
_gl_unregister_fd (int fd)
{
  if (fd >= 0 && fd < dirs_allocated)
    {
      free (dirs[fd].name);
      dirs[fd].name = NULL;
    }
}

/* Mark FD as visiting FILENAME.  FD must be non-negative, and refer
   to an open file descriptor.  If REPLACE_OPEN_DIRECTORY is non-zero,
   this should only be called if FD is visiting a directory.  Close FD
   and return -1 with errno set if there is insufficient memory to track
   the directory name; otherwise return FD.  */
int
_gl_register_fd (int fd, const char *filename)
{
  struct stat statbuf;

  assure (0 <= fd);
  if (REPLACE_OPEN_DIRECTORY
      || (fstat (fd, &statbuf) == 0 && S_ISDIR (statbuf.st_mode)))
    {
      if (!ensure_dirs_slot (fd)
          || (dirs[fd].name = get_name (filename)) == NULL)
        {
          int saved_errno = errno;
          close (fd);
          errno = saved_errno;
          return -1;
        }
    }
  return fd;
}

/* Mark NEWFD as a duplicate of OLDFD; useful from dup, dup2, dup3,
   and fcntl.  Both arguments must be valid and distinct file
   descriptors.  Close NEWFD and return -1 if OLDFD is tracking a
   directory, but there is insufficient memory to track the same
   directory in NEWFD; otherwise return NEWFD.  */
int
_gl_register_dup (int oldfd, int newfd)
{
  assure (0 <= oldfd && 0 <= newfd && oldfd != newfd);
  if (oldfd < dirs_allocated && dirs[oldfd].name)
    {
      /* Duplicated a directory; must ensure newfd is allocated.  */
      if (!ensure_dirs_slot (newfd)
          || (dirs[newfd].name = strdup (dirs[oldfd].name)) == NULL)
        {
          int saved_errno = errno;
          close (newfd);
          errno = saved_errno;
          newfd = -1;
        }
    }
  else if (newfd < dirs_allocated)
    {
      /* Duplicated a non-directory; ensure newfd is cleared.  */
      free (dirs[newfd].name);
      dirs[newfd].name = NULL;
    }
  return newfd;
}

/* If FD is currently visiting a directory, then return the name of
   that directory.  Otherwise, return NULL and set errno.  */
const char *
_gl_directory_name (int fd)
{
  if (0 <= fd && fd < dirs_allocated && dirs[fd].name != NULL)
    return dirs[fd].name;
  /* At this point, fd is either invalid, or open but not a directory.
     If dup2 fails, errno is correctly EBADF.  */
  if (0 <= fd)
    {
      if (dup2 (fd, fd) == fd)
        errno = ENOTDIR;
    }
  else
    errno = EBADF;
  return NULL;
}


/* Implement fchdir() in terms of chdir().  */

int
fchdir (int fd)
{
  const char *name = _gl_directory_name (fd);
  return name ? chdir (name) : -1;
}