1IOCTL_FAT(2) Linux Programmer's Manual IOCTL_FAT(2)
2
6 ioctl_fat - manipulating the FAT filesystem
7
9 #include <linux/msdos_fs.h> /* Definition of [V]FAT_* and
10 ATTR_* constants*/"
11 #include <sys/ioctl.h>
12 int ioctl(int fd, FAT_IOCTL_GET_ATTRIBUTES, uint32_t *attr);
14 int ioctl(int fd, FAT_IOCTL_SET_ATTRIBUTES, uint32_t *attr);
15 int ioctl(int fd, FAT_IOCTL_GET_VOLUME_ID, uint32_t *id);
16 int ioctl(int fd, VFAT_IOCTL_READDIR_BOTH,
17 struct __fat_dirent entry[2]);
18 int ioctl(int fd, VFAT_IOCTL_READDIR_SHORT,
19 struct __fat_dirent entry[2]);
20
22 The ioctl(2) system call can be used to read and write metadata of FAT
23 filesystems that are not accessible using other system calls.
24 Reading and setting file attributes
26 Files and directories in the FAT filesystem possess an attribute bit
27 mask that can be read with FAT_IOCTL_GET_ATTRIBUTES and written with
28 FAT_IOCTL_SET_ATTRIBUTES.
29 The fd argument contains a file descriptor for a file or directory. It
31 is sufficient to create the file descriptor by calling open(2) with the
32 O_RDONLY flag.
33 The attr argument contains a pointer to a bit mask. The bits of the
35 bit mask are:
36 ATTR_RO
38 This bit specifies that the file or directory is read-only.
39 ATTR_HIDDEN
41 This bit specifies that the file or directory is hidden.
42 ATTR_SYS
44 This bit specifies that the file is a system file.
45 ATTR_VOLUME
47 This bit specifies that the file is a volume label. This attri‐
48 bute is read-only.
49 ATTR_DIR
51 This bit specifies that this is a directory. This attribute is
52 read-only.
53 ATTR_ARCH
55 This bit indicates that this file or directory should be
56 archived. It is set when a file is created or modified. It is
57 reset by an archiving system.
58 The zero value ATTR_NONE can be used to indicate that no attribute bit
60 is set.
61 Reading the volume ID
63 FAT filesystems are identified by a volume ID. The volume ID can be
64 read with FAT_IOCTL_GET_VOLUME_ID.
65 The fd argument can be a file descriptor for any file or directory of
67 the filesystem. It is sufficient to create the file descriptor by
68 calling open(2) with the O_RDONLY flag.
69 The id argument is a pointer to the field that will be filled with the
71 volume ID. Typically the volume ID is displayed to the user as a group
72 of two 16-bit fields:
73 printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
75 Reading short filenames of a directory
77 A file or directory on a FAT filesystem always has a short filename
78 consisting of up to 8 capital letters, optionally followed by a period
79 and up to 3 capital letters for the file extension. If the actual
80 filename does not fit into this scheme, it is stored as a long filename
81 of up to 255 UTF-16 characters.
82 The short filenames in a directory can be read with VFAT_IOCTL_READ‐
84 DIR_SHORT. VFAT_IOCTL_READDIR_BOTH reads both the short and the long
85 filenames.
86 The fd argument must be a file descriptor for a directory. It is suf‐
88 ficient to create the file descriptor by calling open(2) with the
89 O_RDONLY flag. The file descriptor can be used only once to iterate
90 over the directory entries by calling ioctl(2) repeatedly.
91 The entry argument is a two-element array of the following structures:
93 struct __fat_dirent {
95 long d_ino;
96 __kernel_off_t d_off;
97 uint32_t short d_reclen;
98 char d_name[256];
99 };
100 The first entry in the array is for the short filename. The second en‐
102 try is for the long filename.
103 The d_ino and d_off fields are filled only for long filenames. The
105 d_ino field holds the inode number of the directory. The d_off field
106 holds the offset of the file entry in the directory. As these values
107 are not available for short filenames, the user code should simply ig‐
108 nore them.
109 The field d_reclen contains the length of the filename in the field
111 d_name. To keep backward compatibility, a length of 0 for the short
112 filename signals that the end of the directory has been reached. How‐
113 ever, the preferred method for detecting the end of the directory is to
114 test the ioctl(2) return value. If no long filename exists, field
115 d_reclen is set to 0 and d_name is a character string of length 0 for
116 the long filename.
117
119 On error, -1 is returned, and errno is set to indicate the error.
120 For VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT a return value
122 of 1 signals that a new directory entry has been read and a return
123 value of 0 signals that the end of the directory has been reached.
124
126 ENOENT This error is returned by VFAT_IOCTL_READDIR_BOTH and
127 VFAT_IOCTL_READDIR_SHORT if the file descriptor fd refers to a
128 removed, but still open directory.
129 ENOTDIR
131 This error is returned by VFAT_IOCTL_READDIR_BOTH and
132 VFAT_IOCTL_READDIR_SHORT if the file descriptor fd does not re‐
133 fer to a directory.
134 ENOTTY The file descriptor fd does not refer to an object in a FAT
136 filesystem.
137 For further error values, see ioctl(2).
139
141 VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT first appeared in
142 Linux 2.0.
143 FAT_IOCTL_GET_ATTRIBUTES and FAT_IOCTL_SET_ATTRIBUTES first appeared in
145 Linux 2.6.12.
146 FAT_IOCTL_GET_VOLUME_ID was introduced in version 3.11 of the Linux
148 kernel.
149
151 This API is Linux-specific.
152
154 Toggling the archive flag
155 The following program demonstrates the usage of ioctl(2) to manipulate
156 file attributes. The program reads and displays the archive attribute
157 of a file. After inverting the value of the attribute, the program
158 reads and displays the attribute again.
159 The following was recorded when applying the program for the file
161 /mnt/user/foo:
162 # ./toggle_fat_archive_flag /mnt/user/foo
164 Archive flag is set
165 Toggling archive flag
166 Archive flag is not set
167 Program source (toggle_fat_archive_flag.c)
169 #include <fcntl.h>
171 #include <linux/msdos_fs.h>
172 #include <stdint.h>
173 #include <stdio.h>
174 #include <stdlib.h>
175 #include <sys/ioctl.h>
176 #include <unistd.h>
177 /*
179 * Read file attributes of a file on a FAT filesystem.
180 * Output the state of the archive flag.
181 */
182 static uint32_t
183 readattr(int fd)
184 {
185 uint32_t attr;
186 int ret;
187 ret = ioctl(fd, FAT_IOCTL_GET_ATTRIBUTES, &attr);
189 if (ret == -1) {
190 perror("ioctl");
191 exit(EXIT_FAILURE);
192 }
193 if (attr & ATTR_ARCH)
195 printf("Archive flag is set\n");
196 else
197 printf("Archive flag is not set\n");
198 return attr;
200 }
201 int
203 main(int argc, char *argv[])
204 {
205 uint32_t attr;
206 int fd;
207 int ret;
208 if (argc != 2) {
210 printf("Usage: %s FILENAME\n", argv[0]);
211 exit(EXIT_FAILURE);
212 }
213 fd = open(argv[1], O_RDONLY);
215 if (fd == -1) {
216 perror("open");
217 exit(EXIT_FAILURE);
218 }
219 /*
221 * Read and display the FAT file attributes.
222 */
223 attr = readattr(fd);
224 /*
226 * Invert archive attribute.
227 */
228 printf("Toggling archive flag\n");
229 attr ^= ATTR_ARCH;
230 /*
232 * Write the changed FAT file attributes.
233 */
234 ret = ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr);
235 if (ret == -1) {
236 perror("ioctl");
237 exit(EXIT_FAILURE);
238 }
239 /*
241 * Read and display the FAT file attributes.
242 */
243 readattr(fd);
244 close(fd);
246 exit(EXIT_SUCCESS);
248 }
249 Reading the volume ID
251 The following program demonstrates the use of ioctl(2) to display the
252 volume ID of a FAT filesystem.
253 The following output was recorded when applying the program for direc‐
255 tory /mnt/user:
256 $ ./display_fat_volume_id /mnt/user
258 Volume ID 6443-6241
259 Program source (display_fat_volume_id.c)
261 #include <fcntl.h>
263 #include <linux/msdos_fs.h>
264 #include <stdint.h>
265 #include <stdio.h>
266 #include <stdlib.h>
267 #include <sys/ioctl.h>
268 #include <unistd.h>
269 int
271 main(int argc, char *argv[])
272 {
273 uint32_t id;
274 int fd;
275 int ret;
276 if (argc != 2) {
278 printf("Usage: %s FILENAME\n", argv[0]);
279 exit(EXIT_FAILURE);
280 }
281 fd = open(argv[1], O_RDONLY);
283 if (fd == -1) {
284 perror("open");
285 exit(EXIT_FAILURE);
286 }
287 /*
289 * Read volume ID.
290 */
291 ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
292 if (ret == -1) {
293 perror("ioctl");
294 exit(EXIT_FAILURE);
295 }
296 /*
298 * Format the output as two groups of 16 bits each.
299 */
300 printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
301 close(fd);
303 exit(EXIT_SUCCESS);
305 }
306 Listing a directory
308 The following program demonstrates the use of ioctl(2) to list a direc‐
309 tory.
310 The following was recorded when applying the program to the directory
312 /mnt/user:
313 $ ./fat_dir /mnt/user
315 . -> ''
316 .. -> ''
317 ALONGF~1.TXT -> 'a long filename.txt'
318 UPPER.TXT -> ''
319 LOWER.TXT -> 'lower.txt'
320 Program source
322 #include <fcntl.h>
323 #include <linux/msdos_fs.h>
324 #include <stdio.h>
325 #include <stdlib.h>
326 #include <sys/ioctl.h>
327 #include <unistd.h>
328 int
330 main(int argc, char *argv[])
331 {
332 struct __fat_dirent entry[2];
333 int fd;
334 int ret;
335 if (argc != 2) {
337 printf("Usage: %s DIRECTORY\n", argv[0]);
338 exit(EXIT_FAILURE);
339 }
340 /*
342 * Open file descriptor for the directory.
343 */
344 fd = open(argv[1], O_RDONLY | O_DIRECTORY);
345 if (fd == -1) {
346 perror("open");
347 exit(EXIT_FAILURE);
348 }
349 for (;;) {
351 /*
353 * Read next directory entry.
354 */
355 ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry);
356 /*
358 * If an error occurs, the return value is -1.
359 * If the end of the directory list has been reached,
360 * the return value is 0.
361 * For backward compatibility the end of the directory
362 * list is also signaled by d_reclen == 0.
363 */
364 if (ret < 1)
365 break;
366 /*
368 * Write both the short name and the long name.
369 */
370 printf("%s -> '%s'\n", entry[0].d_name, entry[1].d_name);
371 }
372 if (ret == -1) {
374 perror("VFAT_IOCTL_READDIR_BOTH");
375 exit(EXIT_FAILURE);
376 }
377 /*
379 * Close the file descriptor.
380 */
381 close(fd);
382 exit(EXIT_SUCCESS);
384 }
385
387 ioctl(2)
388
390 This page is part of release 5.12 of the Linux man-pages project. A
391 description of the project, information about reporting bugs, and the
392 latest version of this page, can be found at
393 https://www.kernel.org/doc/man-pages/.
394Linux 2021-03-22 IOCTL_FAT(2)