ioctl_fat

       #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);

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 label
       FAT filesystems are identified by a volume label.  The volume label can

   Reading short file names 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_READ-
       DIR_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 suf-
       ficient 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.  How-
       ever, the preferred method for detecting the end of the directory is to
       test  the  ioctl()  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.

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.

ERRORS
       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.

       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.

CONFORMING TO
       This API is Linux-specific.

EXAMPLE
   Toggling the archive flag
       The  following  program demonstrates the usage of ioctl() 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
               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 label
       The  following  program demonstrates the use of ioctl(2) to display the
       volume label of a FAT filesystem.

       The following output was recorded when applying the program for  direc-
       tory /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>

               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 %4x-%4x\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 direc-
       tory.

       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
                * 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);
           }

SEE ALSO
       ioctl(2)

COLOPHON
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       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-02-21                      IOCTl-FAT(2)
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