#include <linux/msdos_fs.h>
#include <sys/ioctl.h>
int ioctl(int fd, FAT_IOCTL_GET_ATTRIBUTES, uint32_t *attr);
int ioctl(int fd, FAT_IOCTL_SET_ATTRIBUTES, uint32_t *attr);
int ioctl(int fd, FAT_IOCTL_GET_VOLUME_ID, uint32_t *id);
int ioctl(int fd, VFAT_IOCTL_READDIR_BOTH,
struct __fat_dirent[2] entry);
int ioctl(int fd, VFAT_IOCTL_READDIR_SHORT,
struct __fat_dirent[2] entry);
The fd argument contains a file descriptor for a file or directory. It is sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag.
The attr argument contains a pointer to a bit mask. The bits of the bit mask are:
The zero value ATTR_NONE can be used to indicate that no attribute bit is set.
The fd argument can be a file descriptor for any file or directory of the filesystem. It is sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag.
The id argument is a pointer to the field that will be filled with the volume ID. Typically the volume ID is displayed to the user as a group of two 16-bit fields:
printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
The short filenames in a directory can be read with VFAT_IOCTL_READDIR_SHORT. VFAT_IOCTL_READDIR_BOTH reads both the short and the long filenames.
The fd argument must be a file descriptor for a directory. It is sufficient to create the file descriptor by calling open(2) with the O_RDONLY flag. The file descriptor can be used only once to iterate over the directory entries by calling ioctl(2) repeatedly.
The entry argument is a two-element array of the following structures:
struct __fat_dirent {
long d_ino;
__kernel_off_t d_off;
uint32_t short d_reclen;
char d_name[256];
};
The first entry in the array is for the short filename. The second entry is for the long filename.
The d_ino and d_off fields are filled only for long filenames. The d_ino field holds the inode number of the directory. The d_off field holds the offset of the file entry in the directory. As these values are not available for short filenames, the user code should simply ignore them.
The field d_reclen contains the length of the filename in the field d_name. To keep backward compatibility, a length of 0 for the short filename signals that the end of the directory has been reached. However, the preferred method for detecting the end of the directory is to test the ioctl(2) return value. If no long filename exists, field d_reclen is set to 0 and d_name is a character string of length 0 for the long filename.
For VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT a return value of 1 signals that a new directory entry has been read and a return value of 0 signals that the end of the directory has been reached.
For further error values, see ioctl(2).
FAT_IOCTL_GET_ATTRIBUTES and FAT_IOCTL_SET_ATTRIBUTES first appeared in Linux 2.6.12.
FAT_IOCTL_GET_VOLUME_ID was introduced in version 3.11 of the Linux kernel.
The following was recorded when applying the program for the file /mnt/user/foo:
# ./toggle_fat_archive_flag /mnt/user/foo Archive flag is set Toggling archive flag Archive flag is not set
/*
* Read file attributes of a file on a FAT filesystem.
* Output the state of the archive flag.
*/
static uint32_t
readattr(int fd)
{
uint32_t attr;
int ret;
ret = ioctl(fd, FAT_IOCTL_GET_ATTRIBUTES, &attr);
if (ret == -1) {
perror("ioctl");
exit(EXIT_FAILURE);
}
if (attr & ATTR_ARCH)
printf("Archive flag is set\n");
else
printf("Archive flag is not set\n");
return attr;
}
int
main(int argc, char *argv[])
{
uint32_t attr;
int fd;
int ret;
if (argc != 2) {
printf("Usage: %s FILENAME\n", argv[0]);
exit(EXIT_FAILURE);
}
fd = open(argv[1], O_RDONLY);
if (fd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
/*
* Read and display the FAT file attributes.
*/
attr = readattr(fd);
/*
* Invert archive attribute.
*/
printf("Toggling archive flag\n");
attr ha= ATTR_ARCH;
/*
* Write the changed FAT file attributes.
*/
ret = ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr);
if (ret == -1) {
perror("ioctl");
exit(EXIT_FAILURE);
}
/*
* Read and display the FAT file attributes.
*/
readattr(fd);
close(fd);
The following output was recorded when applying the program for directory /mnt/user:
$ ./display_fat_volume_id /mnt/user Volume ID 6443-6241
int
main(int argc, char *argv[])
{
uint32_t id;
int fd;
int ret;
if (argc != 2) {
printf("Usage: %s FILENAME\n", argv[0]);
exit(EXIT_FAILURE);
}
fd = open(argv[1], O_RDONLY);
if (fd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
/*
* Read volume ID.
*/
ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
if (ret == -1) {
perror("ioctl");
exit(EXIT_FAILURE);
}
/*
* Format the output as two groups of 16 bits each.
*/
printf("Volume ID %04x-%04x\n", id >> 16, id & 0xFFFF);
close(fd);
The following was recorded when applying the program to the directory /mnt/user:
$ ./fat_dir /mnt/user 46 -> '' 46. -> '' ALONGF~1.TXT -> 'a long filename.txt' UPPER.TXT -> '' LOWER.TXT -> 'lower.txt'
int
main(int argc, char *argv[])
{
struct __fat_dirent entry[2];
int fd;
int ret;
if (argc != 2) {
printf("Usage: %s DIRECTORY\n", argv[0]);
exit(EXIT_FAILURE);
}
/*
* Open file descriptor for the directory.
*/
fd = open(argv[1], O_RDONLY | O_DIRECTORY);
if (fd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
for (;;) {
/*
* Read next directory entry.
*/
ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry);
/*
* If an error occurs, the return value is -1.
* If the end of the directory list has been reached,
* the return value is 0.
* For backward compatibility the end of the directory
* list is also signaled by d_reclen == 0.
*/
if (ret < 1)
break;
/*
* Write both the short name and the long name.
*/
printf("%s -> '%s'\n", entry[0].d_name, entry[1].d_name);
}
if (ret == -1) {
perror("VFAT_IOCTL_READDIR_BOTH");
exit(EXIT_FAILURE);
}
/*
* Close the file descriptor.
*/
close(fd);