Hi Heinrich,
On 11/10/2014 11:36 PM, Heinrich Schuchardt 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.
Great work! I have a few comments below.
Let's attempt to widen the review circle. On the next submission,
could you also CC linux-fsdevelo@xxxxxxxxxxxxxxx and
linux-kernel@xxxxxxxxxxxxxxx.
Please also CC the FAT maintainer:
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> ---
> man2/ioctl-fat.2 | 437 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 437 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..ceb3c5f
> --- /dev/null
> +++ b/man2/ioctl-fat.2
I wonder if it might be better to call this page "ioctl_fat.2"
just for consistency with ioctl_list.2. What do you think?
> @@ -0,0 +1,437 @@
> +.\" 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 +.\" manual page may be incorrect or out-of-date.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);
Please bracket the SYNOPSIS with
.nf
.fi
Then you can remove the .br tags. Also, could you manually indent
the lines that wrap (as is done in say mmap.2).
> +.SH DESCRIPTION
> +The
> +.BR ioctl (2)
> +function can be used to read and write metadata of the fat file systems that
I think all instances of "fat" in the text should be "FAT" right?
change all instances of "file system" to "filesystem"
> +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.
Change all instances to "bit mask"
> +The bits of the bitmask are
s/$/:/
> +.TP
> +.B ATTR_RO
> +This bit specifies that the file or directory is read only.
s/read only/read-only/
And other instances below.
> +.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
s/Zero/The zero/
> +.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
s/an file/a file/
s/they/the/
> +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.
s/id/ID/
And in other instances below, including the code comments and the
strings output by the example programs.
> +Typically the volume label is displayed to the user a a group of two
s/Typically/Typically,/
s/a a/as a/
> +16 bit fields.
s/16 bit/16-bt/
> +.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.
s/has to/must/
> +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
s/only be used once/be only used once/
> +entries by calling
> +.BR ioctl (2)
> +repeatedly.
> +.PP
> +The
> +.I entry
> +argument is an array of length two of the following structure.
s/an array of length two of the following structure/
a two-element containing the following structures/
s/\./:/
And add a blank line here.
> +.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
The formatting of the errors section is wrong. You want a .TP
list. See some other *.2 pages for examples.
> +.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
s/archive/the archive/
> +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.
s/attribute/attribute,/
> +.PP
> +The following was recorded when calling the program for file
s/calling/applying/
s/for file/to the file/
> +.IR /mnt/user/foo .
> +.SS Example output
Thanks for these example programs! But, I think the output
could be a little less verbose. In this and the next program,
I think you could drop the following message with no loss of
understanding for the reader:
* Reading FAR attributes
* Closing...
Also, I'd tend to drop the "." at the end of each output
line, but that's mostly a personal taste thing.
(But, I note that your final example does have
instances of "." on the output lines.)
> +.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>
You need to include unistd.h for close(2).
(Best to ensure that all code passes "cc -Wall -Wextra)
Also in the other examples below.
> +
> +/*
> + * 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]);
s/Usage/Usage:/
(and in the other example programs)
> + return EXIT_FAILURE;
> + }
> +
> + printf("Opening %s.\\n", argv[1]);
> + fd = open(argv[1], O_RDONLY);
> + if (fd == \-1) {
> + perror("open");
> + return EXIT_FAILURE;
For consistency with the rest of the code base, I prefer the form
exit(EXIT_...);
Could you all the examples change please.
> + }
> +
> + /*
> + * 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
s/recored/recorded/
> +directory
> +.IR /mnt/user
s/$/ ./
> +.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
s/calling/applying/
s/for directory/to 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>
> +
> +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
> + */
The above comment is formatted differntly from the others.
> + ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry);
> +
> + /*
> + * If an error occurs the return value is \-1.
s/occurs/occurs,/
> + * The end of the directory list is reached when
> + * the d_reclen is zero.
I'd make that last:
Id d_reclen is zero, then 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");
> + return EXIT_FAILURE;
> + }
> +
> + /*
> + * Close the file descriptor.
> + */
> + close(fd);
> +
> + return EXIT_SUCCESS;
> +}
> +.fi
> +.in
> +.SH SEE ALSO
> +.BR ioctl (2)
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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