On Jan 23, 2015, at 12:54 PM, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote:
>
> 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.
>
> Michael Kerrisk suggested to CC linux-fsdevel@xxxxxxxxxxxxxxx and
> linux-kernel@xxxxxxxxxxxxxxx for review.
>
> version 3: correct typos
> version 2: consider comments by Michael Kerrisk
> verison 1: original patch
>
> Signed-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> ---
> man2/ioctl-fat.2 | 442 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 442 insertions(+)
> create mode 100644 man2/ioctl-fat.2
>
> diff --git a/man2/ioctl-fat.2 b/man2/ioctl-fat.2
> new file mode 100644
> index 0000000..80891d8
> --- /dev/null
> +++ b/man2/ioctl-fat.2
> @@ -0,0 +1,442 @@
> +.\" 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 +.\" manual page may be incorrect or out-of-date.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.
There are extraneous periods at the end of each of these lines.
> +.\" 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 2015-01-23 "Linux" "Linux Programmer's Manual"
> +.SH "NAME"
> +ioctl-fat \- manipulating the FAT filesystem
> +.SH SYNOPSIS
> +.nf
> +.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);
> +.BI "int ioctl(int " fd ", FAT_IOCTL_SET_ATTRIBUTES, uint32_t * " attr);
> +.BI "int ioctl(int " fd ", FAT_IOCTL_GET_VOLUME_ID, uint32_t * " id);
> +.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_BOTH,
> +.BI " struct __fat_dirent[2] " entry);
> +.BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_SHORT,
> +.BI " struct __fat_dirent[2] " entry);
> +.SH DESCRIPTION
> +The
> +.BR ioctl (2)
> +function can be used to read and write metadata of the FAT filesystems 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 bit mask.
> +The bits of the bit mask are
> +.TP
> +.B ATTR_RO
> +This bit specifies that the file or directory is read-only.
It's too bad that these constants have such generic names. It would
be better to use MSDOS_ATTR_* or FAT_ATTR_*, since these are also
exposed to userspace, but are only used by FAT.
> +.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.
It might be useful if the FS_IOC_GETFLAGS ioctl was implemented for
FAT, and this was mapped to FS_IMMUTABLE_FL as it is in the kernel,
so that the more common lsattr and chattr commands worked on it, as
they do with ext*, btrfs, xfs, reiserfs, etc.
I guess these aren't problems with the man page per-se, but something
for the FAT developers to think about.
Cheers, Andreas
> +.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
> +The zero value
> +.B ATTR_NONE
> +can be used to indicate that no attribute bit is set.
> +.SS Reading the volume label
> +Fat filesystems 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 a file descriptor for any file or directory of the
> +filesystem.
> +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 as 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 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.
> +.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 must 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 be only used once to iterate over the directory
> +entries by calling
> +.BR ioctl (2)
> +repeatedly.
> +.PP
> +The
> +.I entry
> +argument is a two-element array of the following structures.
> +
> +.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
> +.TP
> +.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.
> +.TP
> +.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 VERSIONS
> +.B FAT_IOCTL_GET_VOLUME_ID
> +was introduced in version 3.11 of the Linux kernel.
> +.PP
> +.BR FAT_IOCTL_GET_ATTRIBUTES ,
> +.BR FAT_IOCTL_SET_ATTRIBUTES ,
> +.BR VFAT_IOCTL_READDIR_BOTH ,
> +and
> +.B VFAT_IOCTL_READDIR_SHORT
> +were introduced before version 2.6.28 of the Linux kernel.
> +.SH "CONFORMING TO"
> +This API is Linux-specific.
> +.SH EXAMPLE
> +.SS Toggling the 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 applying the program for the file
> +.IR /mnt/user/foo .
> +.SS Example output
> +.in +4n
> +.nf
> +# ./toggle_archive_flag /mnt/user/foo
> +Archive flag is set
> +Toggling archive flag
> +Archive flag is not set
> +.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>
> +#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);
> +
> + 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 filesystem.
> +.PP
> +The following output was recorded when applying the program for
> +directory
> +.IR /mnt/user .
> +.SS Example output
> +.in +4n
> +.nf
> +$ ./display_volume_id /mnt/user
> +Volume ID 6443-6241
> +.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>
> +#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 %4x\-%4x\\n", id >> 16, id & 0xFFFF);
> +
> + 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 applying the program for the 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>
> +#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 d_reclen is zero, the end of the directory
> + * list has been reached.
> + */
> + 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");
> + exit(EXIT_FAILURE);
> + }
> +
> + /*
> + * Close the file descriptor.
> + */
> + close(fd);
> +
> + return EXIT_SUCCESS;
> +}
> +.fi
> +.in
> +.SH SEE ALSO
> +.BR ioctl (2)
> --
> 2.1.4
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
Cheers, Andreas
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
