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man:ioctl_fat

IOCTL-FAT(2) Linux Programmer's Manual IOCTL-FAT(2)

NAME

     ioctl_fat - manipulating the FAT filesystem

SYNOPSIS

     #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 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 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(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.

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.
     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).

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.

CONFORMING TO

     This API is Linux-specific.

EXAMPLE

 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 Tog-
         gling 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 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>  #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 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 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); }

SEE ALSO

     ioctl(2)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 IOCTL-FAT(2)

/data/webs/external/dokuwiki/data/pages/man/ioctl_fat.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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