The ioctl(2) system call may be used to retrieve information about
the fat file system and to set file attributes.
This new manpage describes the details.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
---
man2/ioctl-fat.2 | 437 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 437 insertions(+)
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+.\" Copyright (C) 2014, Heinrich Schuchardt <xypron.glpk@xxxxxx>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of
+.\" this manual under the conditions for verbatim copying, provided that
+.\" the entire resulting derived work is distributed under the terms of
+.\" a permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date. The author(s) assume.
+.\" no responsibility for errors or omissions, or for damages resulting.
+.\" from the use of the information contained herein. The author(s) may.
+.\" not have taken the same level of care in the production of this.
+.\" manual, which is licensed free of charge, as they might when working.
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.TH IOCTl-FAT 2 2014-11-10 "Linux" "Linux Programmer's Manual"
+.SH "NAME"
+ioctl-fat \- manipulating the fat file system
+.SH SYNOPSIS
+.B #include <linux/msdos_fs.h>
+.br
+.B #include <sys/ioctl.h>
+.sp
+.BI "int ioctl(int " fd ", FAT_IOCTL_GET_ATTRIBUTES, uint32_t * " attr);
+.br
+.BI "int ioctl(int " fd ", FAT_IOCTL_SET_ATTRIBUTES, uint32_t * " attr);
+.br
+.BI "int ioctl(int " fd ", FAT_IOCTL_GET_VOLUME_ID, uint32_t * " id);
+.br
+.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_BOTH, struct __fat_dirent[2] " entry);
+.br
+.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_SHORT, struct __fat_dirent[2] " entry);
+.SH DESCRIPTION
+The
+.BR ioctl (2)
+function can be used to read and write metadata of the fat file systems that
+are not accessible using other system calls.
+.SS Reading and setting file attributes
+Files and directories in the fat filesystem possess an attribute bit mask that
+can be read with
+.B FAT_IOCTL_GET_ATTRIBUTES
+and written with
+.BR FAT_IOCTL_SET_ATTRIBUTES .
+.PP
+The
+.I fd
+argument contains a file descriptor for the file or directory.
+It is sufficient to create the file descriptor by calling
+.BR open (2)
+with the
+.B O_RDONLY
+flag.
+.PP
+The
+.I attr
+argument contains a pointer to the bitmask.
+The bits of the bitmask are
+.TP
+.B ATTR_RO
+This bit specifies that the file or directory is read only.
+.TP
+.B ATTR_HIDDEN
+This bit specifies that the file or directory is hidden.
+.TP
+.B ATTR_SYS
+This bit specifies that the file is a system file.
+.TP
+.B ATTR_VOLUME
+This bit specifies that the file is a volume label.
+This attribute is read only.
+.TP
+.B ATTR_DIR
+This bit specifies that this is a directory.
+This attribute is read only.
+.TP
+.B 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.
+.PP
+Zero value
+.B ATTR_NONE
+can be used to indicate that no attribute bit is set.
+.SS Reading the volume label
+Fat file systems are identified by a volume label.
+The volume label can be read with
+.BR FAT_IOCTL_GET_VOLUME_ID .
+.PP
+The
+.I fd
+argument can be an file descriptor for any file or directory of they
+file system.
+It is sufficient to create the file descriptor by calling
+.BR open (2)
+with the
+.B O_RDONLY
+flag.
+.PP
+The
+.I id
+argument is a pointer to the field that will be filled with the volume id.
+Typically the volume label is displayed to the user a a group of two
+16 bit fields.
+.PP
+.in +4n
+.nf
+printf("Volume id %4x-%4x\n", id >> 16, id & 0xFFFF);
+.fi
+.in
+.SS Reading short file names of a directory
+A file or directory on a fat file system 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.
+.PP
+The short filenames in a directory can be read with
+.BR VFAT_IOCTL_READDIR_SHORT .
+.B VFAT_IOCTL_READDIR_BOTH
+reads both the short and the long filenames.
+.PP
+The
+.I fd
+argument has to be a file descriptor for a directory.
+It is sufficient to create the file descriptor by calling
+.BR open (2)
+with the
+.B O_RDONLY
+flag.
+The file descriptor can only be used once to iterate over the directory
+entries by calling
+.BR ioctl (2)
+repeatedly.
+.PP
+The
+.I entry
+argument is an array of length two of the following structure.
+.in +4n
+.nf
+struct __fat_dirent {
+ long d_ino;
+ __kernel_off_t d_off;
+ uint32_t short d_reclen;
+ char d_name[256];
+};
+.fi
+.in
+.PP
+The first entry in the array is for the short filename.
+The second entry is for the long filename.
+.PP
+Field
+.I d_reclen
+specifies the length of the filename in field
+.IR d_name .
+A length of 0 for the short filename signals that the end of the directory
+has been reached.
+.SH RETURN VALUE
+On error, -1 is returned, and errno is set to indicate the error.
+.SH ERRORS
+.B ENOTDIR
+This error is returned by
+.B VFAT_IOCTL_READDIR_SHORT
+and
+.B VFAT_IOCTL_READDIR_SHORT
+if the file descriptor does not point to a directory.
+.PP
+.B ENOTTY
+This error signals that the file descriptor is not for a fat filesystem.
+.PP
+For further error values see
+.BR ioctl (2).
+.SH EXAMPLE
+.SS Toggling archive flag
+The following program demonstrates the usage of the ioctl API to manipulate
+file attributes.
+It reads and displays the archive attribute of a file.
+After inverting the value of the attribute it reads and displays it again.
+.PP
+The following was recorded when calling the program for file
+.IR /mnt/user/foo .
+.SS Example output
+.in +4n
+.nf
+# ./toggle_archive_flag /mnt/user/foo
+Opening /mnt/user/foo.
+Reading FAT attributes.
+Archive flag is set.
+Toggling archive attribute.
+Reading FAT attributes.
+Archive flag is not set.
+Closing /mnt/user/foo.
+.fi
+.in
+.SS Program source
+.in +4n
+.nf
+#include <fcntl.h>
+#include <linux/msdos_fs.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+
+/*
+ * Read file attributes of a file on a FAT file system.
+ * Output the state of the archive flag.
+ */
+static uint32_t
+readattr(int fd)
+{
+ uint32_t attr;
+ int ret;
+
+ printf("Reading FAT attributes.\\n");
+ 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]);
+ return EXIT_FAILURE;
+ }
+
+ printf("Opening %s.\\n", argv[1]);
+ fd = open(argv[1], O_RDONLY);
+ if (fd == \-1) {
+ perror("open");
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Read and display the FAT file attributes.
+ */
+ attr = readattr(fd);
+
+ /*
+ * Invert archive attribute.
+ */
+ printf("Toggling archive attribute.\\n");
+ attr ^= ATTR_ARCH;
+
+ /*
+ * Write the changed FAT file attributes.
+ */
+ ret = ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr);
+ if (ret == \-1) {
+ perror("ioctl");
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Read and display the FAT file attributes.
+ */
+ readattr(fd);
+
+ printf("Closing %s.\\n", argv[1]);
+ close(fd);
+
+ return EXIT_SUCCESS;
+}
+.fi
+.in
+.SS Reading the volume label
+The following program demonstrates the usage of the ioctl API to
+display the volume label of a fat file system.
+.PP
+The following output was recored when calling the program for
+directory
+.IR /mnt/user
+.SS Example output
+.in +4n
+.nf
+$ ./display_volume_id /mnt/user
+Opening /mnt/user
+Volume id 6443-6241
+Closing /mnt/user
+.fi
+.in
+.SS Program source
+.in +4n
+.nf
+#include <fcntl.h>
+#include <linux/msdos_fs.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+
+int
+main(int argc, char *argv[])
+{
+ uint32_t id;
+ int fd;
+ int ret;
+
+ if (argc != 2) {
+ printf("Usage %s FILENAME\\n", argv[0]);
+ return EXIT_FAILURE;
+ }
+
+ printf("Opening %s\\n", argv[1]);
+ fd = open(argv[1], O_RDONLY);
+ if (fd == \-1) {
+ perror("open");
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Read volume id.
+ */
+ ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id);
+ if (ret == \-1) {
+ perror("ioctl");
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Format the output as two groups of 16 bits each.
+ */
+ printf("Volume id %4x\-%4x\\n", id >> 16, id & 0xFFFF);
+
+ printf("Closing %s\\n", argv[1]);
+ close(fd);
+
+ return EXIT_SUCCESS;
+}
+.fi
+.in
+.SS Listing a directory
+The following program demonstrates the usage of the ioctl API to
+list a directory.
+.PP
+The following was recorded when calling the program for directory
+.IR /mnt/user .
+.SS Example output
+.in +4n
+.nf
+$ ./fat_dir /mnt/user
+\[char46] -> ''
+\[char46]. -> ''
+ALONGF~1.TXT -> 'a long filename.txt'
+UPPER.TXT -> ''
+LOWER.TXT -> 'lower.txt'
+.fi
+.in
+.SS Program source
+.in +4n
+.nf
+#include <fcntl.h>
+#include <linux/msdos_fs.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.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]);
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Open file descriptor for the directory.
+ */
+ fd = open(argv[1], O_RDONLY | O_DIRECTORY);
+ if (fd == \-1) {
+ perror("open");
+ return EXIT_FAILURE;
+ }
+
+ for (;;) {
+
+ /*
+ * read next directory entry
+ */
+ ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry);
+
+ /*
+ * If an error occurs the return value is \-1.
+ * The end of the directory list is reached when
+ * the d_reclen is zero.
+ */
+ if (ret == \-1 || entry[0].d_reclen == 0)
+ 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");
+ return EXIT_FAILURE;
+ }
+
+ /*
+ * Close the file descriptor.
+ */
+ close(fd);
+
+ return EXIT_SUCCESS;
+}
+.fi
+.in
+.SH SEE ALSO
+.BR ioctl (2)
--
2.1.1
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