манипулирование файловой системой FAT (manipulating the FAT filesystem)
Имя (Name)
ioctl_fat - manipulating the FAT filesystem
Синопсис (Synopsis)
#include <linux/msdos_fs.h> /* Definition of [V]FAT_* and
ATTR_* constants*/"
#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 entry[2]);
int ioctl(int fd, VFAT_IOCTL_READDIR_SHORT,
struct __fat_dirent entry[2]);
Описание (Description)
The ioctl(2) system call can be used to read and write metadata
of FAT filesystems that are not accessible using other system
calls.
Reading and setting file attributes
Files and directories in the FAT filesystem possess an attribute
bit mask that can be read with FAT_IOCTL_GET_ATTRIBUTES and
written with FAT_IOCTL_SET_ATTRIBUTES.
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:
ATTR_RO
This bit specifies that the file or directory is read-
only.
ATTR_HIDDEN
This bit specifies that the file or directory is hidden.
ATTR_SYS
This bit specifies that the file is a system file.
ATTR_VOLUME
This bit specifies that the file is a volume label. This
attribute is read-only.
ATTR_DIR
This bit specifies that this is a directory. This
attribute is read-only.
ATTR_ARCH
This bit indicates that this file or directory should be
archived. It is set when a file is created or modified.
It is reset by an archiving system.
The zero value ATTR_NONE can be used to indicate that no
attribute bit is set.
Reading the volume ID
FAT filesystems are identified by a volume ID. The volume ID can
be read with FAT_IOCTL_GET_VOLUME_ID.
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);
Reading short filenames of a directory
A file or directory on a FAT filesystem always has a short
filename consisting of up to 8 capital letters, optionally
followed by a period and up to 3 capital letters for the file
extension. If the actual filename does not fit into this scheme,
it is stored as a long filename of up to 255 UTF-16 characters.
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.
Возвращаемое значение (Return value)
On error, -1 is returned, and errno is set to indicate the error.
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.
Ошибки (Error)
ENOENT This error is returned by VFAT_IOCTL_READDIR_BOTH and
VFAT_IOCTL_READDIR_SHORT if the file descriptor fd refers
to a removed, but still open directory.
ENOTDIR
This error is returned by VFAT_IOCTL_READDIR_BOTH and
VFAT_IOCTL_READDIR_SHORT if the file descriptor fd does
not refer to a directory.
ENOTTY The file descriptor fd does not refer to an object in a
FAT filesystem.
For further error values, see ioctl(2).
Версии (Versions)
VFAT_IOCTL_READDIR_BOTH and VFAT_IOCTL_READDIR_SHORT first
appeared in Linux 2.0.
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.
Стандарты (Conforming to)
This API is Linux-specific.
Примеры (Examples)
Toggling the archive flag
The following program demonstrates the usage of ioctl(2) to
manipulate file attributes. The program reads and displays the
archive attribute of a file. After inverting the value of the
attribute, the program reads and displays the attribute again.
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
Program source (toggle_fat_archive_flag.c)
#include <fcntl.h>
#include <linux/msdos_fs.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
/*
* 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 ^= 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);
exit(EXIT_SUCCESS);
}
Reading the volume ID
The following program demonstrates the use of ioctl(2) to display
the volume ID of a FAT filesystem.
The following output was recorded when applying the program for
directory /mnt/user:
$ ./display_fat_volume_id /mnt/user
Volume ID 6443-6241
Program source (display_fat_volume_id.c)
#include <fcntl.h>
#include <linux/msdos_fs.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
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);
exit(EXIT_SUCCESS);
}
Listing a directory
The following program demonstrates the use of ioctl(2) to list a
directory.
The following was recorded when applying the program to the
directory /mnt/user:
$ ./fat_dir /mnt/user
. -> ''
.. -> ''
ALONGF~1.TXT -> 'a long filename.txt'
UPPER.TXT -> ''
LOWER.TXT -> 'lower.txt'
Program source
#include <fcntl.h>
#include <linux/msdos_fs.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
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);
exit(EXIT_SUCCESS);
}
Смотри также (See also)
ioctl(2)
