1IOCTL-FAT(2)               Linux Programmer's Manual              IOCTL-FAT(2)
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3
4

NAME

6       ioctl_fat - manipulating the FAT filesystem
7

SYNOPSIS

9       #include <linux/msdos_fs.h>
10       #include <sys/ioctl.h>
11
12       int ioctl(int fd, FAT_IOCTL_GET_ATTRIBUTES, uint32_t *attr);
13       int ioctl(int fd, FAT_IOCTL_SET_ATTRIBUTES, uint32_t *attr);
14       int ioctl(int fd, FAT_IOCTL_GET_VOLUME_ID, uint32_t *id);
15       int ioctl(int fd, VFAT_IOCTL_READDIR_BOTH,
16                 struct __fat_dirent[2] entry);
17       int ioctl(int fd, VFAT_IOCTL_READDIR_SHORT,
18                 struct __fat_dirent[2] entry);
19

DESCRIPTION

21       The  ioctl(2) system call can be used to read and write metadata of FAT
22       filesystems that are not accessible using other system calls.
23
24   Reading and setting file attributes
25       Files and directories in the FAT filesystem possess  an  attribute  bit
26       mask  that  can  be read with FAT_IOCTL_GET_ATTRIBUTES and written with
27       FAT_IOCTL_SET_ATTRIBUTES.
28
29       The fd argument contains a file descriptor for a file or directory.  It
30       is sufficient to create the file descriptor by calling open(2) with the
31       O_RDONLY flag.
32
33       The attr argument contains a pointer to a bit mask.  The  bits  of  the
34       bit mask are:
35
36       ATTR_RO
37              This bit specifies that the file or directory is read-only.
38
39       ATTR_HIDDEN
40              This bit specifies that the file or directory is hidden.
41
42       ATTR_SYS
43              This bit specifies that the file is a system file.
44
45       ATTR_VOLUME
46              This  bit  specifies  that  the  file  is  a volume label.  This
47              attribute is read-only.
48
49       ATTR_DIR
50              This bit specifies that this is a directory.  This attribute  is
51              read-only.
52
53       ATTR_ARCH
54              This  bit  indicates  that  this  file  or  directory  should be
55              archived.  It is set when a file is created or modified.  It  is
56              reset by an archiving system.
57
58       The  zero value ATTR_NONE can be used to indicate that no attribute bit
59       is set.
60
61   Reading the volume ID
62       FAT filesystems are identified by a volume ID.  The volume  ID  can  be
63       read with FAT_IOCTL_GET_VOLUME_ID.
64
65       The  fd  argument can be a file descriptor for any file or directory of
66       the filesystem.  It is sufficient to  create  the  file  descriptor  by
67       calling open(2) with the O_RDONLY flag.
68
69       The  id argument is a pointer to the field that will be filled with the
70       volume ID.  Typically the volume ID is displayed to the user as a group
71       of two 16-bit fields:
72
73           printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
74
75   Reading short file names of a directory
76       A  file  or  directory  on a FAT filesystem always has a short filename
77       consisting of up to 8 capital letters, optionally followed by a  period
78       and  up  to  3  capital  letters for the file extension.  If the actual
79       filename does not fit into this scheme, it is stored as a long filename
80       of up to 255 UTF-16 characters.
81
82       The  short  filenames  in a directory can be read with VFAT_IOCTL_READ‐
83       DIR_SHORT.  VFAT_IOCTL_READDIR_BOTH reads both the short and  the  long
84       filenames.
85
86       The  fd argument must be a file descriptor for a directory.  It is suf‐
87       ficient to create the file  descriptor  by  calling  open(2)  with  the
88       O_RDONLY  flag.   The  file descriptor can be used only once to iterate
89       over the directory entries by calling ioctl(2) repeatedly.
90
91       The entry argument is a two-element array of the following structures:
92
93           struct __fat_dirent {
94               long            d_ino;
95               __kernel_off_t  d_off;
96               uint32_t short  d_reclen;
97               char            d_name[256];
98           };
99
100       The first entry in the array is for the  short  filename.   The  second
101       entry is for the long filename.
102
103       The  d_ino  and  d_off  fields are filled only for long filenames.  The
104       d_ino field holds the inode number of the directory.  The  d_off  field
105       holds  the  offset of the file entry in the directory.  As these values
106       are not available for short filenames,  the  user  code  should  simply
107       ignore them.
108
109       The  field  d_reclen  contains  the length of the filename in the field
110       d_name.  To keep backward compatibility, a length of 0  for  the  short
111       filename  signals that the end of the directory has been reached.  How‐
112       ever, the preferred method for detecting the end of the directory is to
113       test  the  ioctl(2)  return  value.   If no long filename exists, field
114       d_reclen is set to 0 and d_name is a character string of length  0  for
115       the long filename.
116

RETURN VALUE

118       On error, -1 is returned, and errno is set to indicate the error.
119
120       For VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT a return value
121       of 1 signals that a new directory entry has  been  read  and  a  return
122       value of 0 signals that the end of the directory has been reached.
123

ERRORS

125       ENOENT This   error   is   returned   by   VFAT_IOCTL_READDIR_BOTH  and
126              VFAT_IOCTL_READDIR_SHORT if the file descriptor fd refers  to  a
127              removed, but still open directory.
128
129       ENOTDIR
130              This   error   is   returned   by   VFAT_IOCTL_READDIR_BOTH  and
131              VFAT_IOCTL_READDIR_SHORT if the  file  descriptor  fd  does  not
132              refer to a directory.
133
134       ENOTTY The  file  descriptor  fd  does  not refer to an object in a FAT
135              filesystem.
136
137       For further error values, see ioctl(2).
138

VERSIONS

140       VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT first appeared  in
141       Linux 2.0.
142
143       FAT_IOCTL_GET_ATTRIBUTES and FAT_IOCTL_SET_ATTRIBUTES first appeared in
144       Linux 2.6.12.
145
146       FAT_IOCTL_GET_VOLUME_ID was introduced in version  3.11  of  the  Linux
147       kernel.
148

CONFORMING TO

150       This API is Linux-specific.
151

EXAMPLE

153   Toggling the archive flag
154       The  following program demonstrates the usage of ioctl(2) to manipulate
155       file attributes.  The program reads and displays the archive  attribute
156       of  a  file.   After  inverting the value of the attribute, the program
157       reads and displays the attribute again.
158
159       The following was recorded when  applying  the  program  for  the  file
160       /mnt/user/foo:
161
162           # ./toggle_fat_archive_flag /mnt/user/foo
163           Archive flag is set
164           Toggling archive flag
165           Archive flag is not set
166
167   Program source (toggle_fat_archive_flag.c)
168
169       #include <fcntl.h>
170       #include <linux/msdos_fs.h>
171       #include <stdint.h>
172       #include <stdio.h>
173       #include <stdlib.h>
174       #include <sys/ioctl.h>
175       #include <unistd.h>
176
177       /*
178        * Read file attributes of a file on a FAT filesystem.
179        * Output the state of the archive flag.
180        */
181       static uint32_t
182       readattr(int fd)
183       {
184           uint32_t attr;
185           int ret;
186
187           ret = ioctl(fd, FAT_IOCTL_GET_ATTRIBUTES, &attr);
188           if (ret == -1) {
189               perror("ioctl");
190               exit(EXIT_FAILURE);
191           }
192
193           if (attr & ATTR_ARCH)
194               printf("Archive flag is set\n");
195           else
196               printf("Archive flag is not set\n");
197
198           return attr;
199       }
200
201       int
202       main(int argc, char *argv[])
203       {
204           uint32_t attr;
205           int fd;
206           int ret;
207
208           if (argc != 2) {
209               printf("Usage: %s FILENAME\n", argv[0]);
210               exit(EXIT_FAILURE);
211           }
212
213           fd = open(argv[1], O_RDONLY);
214           if (fd == -1) {
215               perror("open");
216               exit(EXIT_FAILURE);
217           }
218
219           /*
220            * Read and display the FAT file attributes.
221            */
222           attr = readattr(fd);
223
224           /*
225            * Invert archive attribute.
226            */
227           printf("Toggling archive flag\n");
228           attr ^= ATTR_ARCH;
229
230           /*
231            * Write the changed FAT file attributes.
232            */
233           ret = ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr);
234           if (ret == -1) {
235               perror("ioctl");
236               exit(EXIT_FAILURE);
237           }
238
239           /*
240            * Read and display the FAT file attributes.
241            */
242           readattr(fd);
243
244           close(fd);
245
246           exit(EXIT_SUCCESS);
247       }
248
249   Reading the volume ID
250       The  following  program demonstrates the use of ioctl(2) to display the
251       volume ID of a FAT filesystem.
252
253       The following output was recorded when applying the program for  direc‐
254       tory /mnt/user:
255
256           $ ./display_fat_volume_id /mnt/user
257           Volume ID 6443-6241
258
259   Program source (display_fat_volume_id.c)
260
261       #include <fcntl.h>
262       #include <linux/msdos_fs.h>
263       #include <stdint.h>
264       #include <stdio.h>
265       #include <stdlib.h>
266       #include <sys/ioctl.h>
267       #include <unistd.h>
268
269       int
270       main(int argc, char *argv[])
271       {
272           uint32_t id;
273           int fd;
274           int ret;
275
276           if (argc != 2) {
277               printf("Usage: %s FILENAME\n", argv[0]);
278               exit(EXIT_FAILURE);
279           }
280
281           fd = open(argv[1], O_RDONLY);
282           if (fd == -1) {
283               perror("open");
284               exit(EXIT_FAILURE);
285           }
286
287           /*
288            * Read volume ID.
289            */
290           ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
291           if (ret == -1) {
292               perror("ioctl");
293               exit(EXIT_FAILURE);
294           }
295
296           /*
297            * Format the output as two groups of 16 bits each.
298            */
299           printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
300
301           close(fd);
302
303           exit(EXIT_SUCCESS);
304       }
305
306   Listing a directory
307       The following program demonstrates the use of ioctl(2) to list a direc‐
308       tory.
309
310       The following was recorded when applying the program to  the  directory
311       /mnt/user:
312
313           $ ./fat_dir /mnt/user
314           . -> ''
315           .. -> ''
316           ALONGF~1.TXT -> 'a long filename.txt'
317           UPPER.TXT -> ''
318           LOWER.TXT -> 'lower.txt'
319
320   Program source
321           #include <fcntl.h>
322           #include <linux/msdos_fs.h>
323           #include <stdio.h>
324           #include <stdlib.h>
325           #include <sys/ioctl.h>
326           #include <unistd.h>
327
328           int
329           main(int argc, char *argv[])
330           {
331               struct __fat_dirent entry[2];
332               int fd;
333               int ret;
334
335               if (argc != 2) {
336                   printf("Usage: %s DIRECTORY\n", argv[0]);
337                   exit(EXIT_FAILURE);
338               }
339
340               /*
341                * Open file descriptor for the directory.
342                */
343               fd = open(argv[1], O_RDONLY | O_DIRECTORY);
344               if (fd == -1) {
345                   perror("open");
346                   exit(EXIT_FAILURE);
347               }
348
349               for (;;) {
350
351                   /*
352                    * Read next directory entry.
353                    */
354                   ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry);
355
356                   /*
357                    * If an error occurs, the return value is -1.
358                    * If the end of the directory list has been reached,
359                    * the return value is 0.
360                    * For backward compatibility the end of the directory
361                    * list is also signaled by d_reclen == 0.
362                    */
363                   if (ret < 1)
364                       break;
365
366                   /*
367                    * Write both the short name and the long name.
368                    */
369                   printf("%s -> '%s'\n", entry[0].d_name, entry[1].d_name);
370               }
371
372               if (ret == -1) {
373                   perror("VFAT_IOCTL_READDIR_BOTH");
374                   exit(EXIT_FAILURE);
375               }
376
377               /*
378                * Close the file descriptor.
379                */
380               close(fd);
381
382               exit(EXIT_SUCCESS);
383           }
384

SEE ALSO

386       ioctl(2)
387

COLOPHON

389       This  page  is  part of release 5.04 of the Linux man-pages project.  A
390       description of the project, information about reporting bugs,  and  the
391       latest     version     of     this    page,    can    be    found    at
392       https://www.kernel.org/doc/man-pages/.
393
394
395
396Linux                             2019-03-06                      IOCTL-FAT(2)
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