libisoburn/xorriso/README_gnu_xorriso

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      Contribution of libburnia-project.org to the GNU Operating System
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GNU xorriso. By Thomas Schmitt <scdbackup@gmx.net>
Derived from and supported by libburnia-project.org, published via:
http://www.gnu.org/software/xorriso/xorriso_eng.html
ftp://ftp.gnu.org/gnu/xorriso/xorriso-0.5.0.tar.gz
Provided under GPL version 3 or later. No warranty.
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xorriso is a program which copies file objects from POSIX compliant
filesystems into Rock Ridge enhanced ISO 9660 filesystems and allows
session-wise manipulation of such filesystems. It can load the management
information of existing ISO images and it writes the session results to
optical media or to filesystem objects.
Vice versa xorriso is able to restore file objects from ISO 9660 filesystems.

A special property of xorriso is that it needs neither an external ISO 9660
formatter program nor an external burn program for CD or DVD but rather
incorporates the libraries of libburnia-project.org .

Currently it is fully supported on GNU/Linux with kernels >= 2.4 and on
FreeBSD versions with ATAPI/CAM support enabled in the kernel, see atapicam(4).
On other X/Open compliant systems there will only be POSIX i/o with disk
file objects, but no direct MMC operation on CD/DVD/BD drives.

By using this software you agree to the disclaimer at the end of this text:
"... without even the implied warranty ..."


                   Compilation, First Glimpse, Installation

The most simple way to get xorriso from source code is the xorriso standalone
tarball.

Prerequisites:
The tarball contains everything that is needed except the following system
components:
   libc, libpthread
   plus on FreeBSD: libiconv, libcam, IDE and SATA drives need atapicam
Optional at compile time are:
   libreadline and the readline-dev headers make dialog mode more convenient.
   on GNU/Linux: libacl and libacl-devel allow getting and setting ACLs.
   zlib and zlib-devel allow zisofs compression.
If they were present at compile time, then the optional libraries have to
be present at runtime, too.

Obtain xorriso-0.5.0.tar.gz, take it to a directory of your choice and do:

    tar xzf xorriso-0.5.0.tar.gz
    cd xorriso-0.5.0

Within that directory execute:

    ./configure --prefix=/usr
    make

This will produce a binary named
    ./xorriso/xorriso

If you want xorriso to report a "Build timestamp" with its option -version :
    make buildstamped

You may strip the binary to reduce it in size
    strip ./xorriso/xorriso

You may copy or move it to a directory where it can be found by the shell,
or you may execute xorriso at the place where it was built,
or you may execute as superuser:
    make install

For general concepts, options and usage examples see
    man 1 xorriso

This man page is part of the tarball as
    xorriso/xorriso.1
You may get a first glimpse by
    man ./xorriso/xorriso.1

It gets installed with "make install" but may also be placed manually in the
./man1 directory below one of the directories mentioned in environment
variable $MANPATH.

The installation creates several alias links pointing to the xorriso binary:
    xorrisofs  starts xorriso with -as mkisofs emulation already enabled
    xorrecord  starts xorriso with -as cdrecord emulation already enabled
    osirrox    starts with -osirrox image-to-disk copying already enabled

If you want to avoid dependecy on libreadline although the libreadline
development package is installed, then rather build xorriso by:
    ./configure --prefix=/usr --disable-libreadline 
    make clean ; make
Never omit the "make clean" command after switching libreadline enabling.
Other deliberate dependency reduction options of ./configure are:
    --disable-libacl   avoid use of ACL functions like acl_to_text()
    --disable-xattr    avoid use of xattr functions like listxattr()
    --disable-zlib     avoid use of zlib functions like compress2()

xorriso brings own system adapters which allow burning optical media on
GNU/Linux and FreeBSD. Alternatively it can use libcdio-0.83 or later for
sending commands to optical drives:
    --enable-libcdio

xorriso allows to use external processes as file content filters. This is
a potential security risk which may be avoided by ./configure option
    --disable-external-filters

By default the filter feature is disabled if effective user id and real
user id differ. This ban can be lifted by
    --enable-external-filters-setuid

Sometimes xorriso will yield better write performance on GNU/Linux if 64 KB are
transmitted in each write operation rather than 32 KB. See option -dvd_obs .
64k can be made default at configure time by:
    --enable-dvd-obs-64k

For xorriso -as cdrecord emulation only:
In some situations GNU/Linux may deliver a better write performance to drives
if the track input is read with O_DIRECT (see man 2 open). The included libburn
and the cdrecord emulation of xorriso can be told to use this peculiar read
mode by:
    --enable-track-src-odirect


                       Drives and Disk File Objects 

The user of libisoburn applications needs rw-permission for the CD/DVD/BD
drives which shall be used, even if only reading is intended.
A list of rw-accessible drives can be obtained by

    xorriso -devices

CD devices which offer no rw-permission are invisible to normal users.
The superuser should be able to see any usable drive and then set the
permissions as needed.

The output of  xorriso -devices  might look like

0  -dev '/dev/sr0' rwrw-- :  'TSSTcorp' 'CDDVDW SH-S203B' 
1  -dev '/dev/hda' rwrw-- :  'HL-DT-ST' 'DVD-ROM GDR8162B' 

Full and insecure enabling of both for everybody would look like
    chmod a+rw /dev/sr0 /dev/hda
This is equivalent to the traditional setup chmod a+x,u+s cdrecord.

I strongly discourage to run xorriso with setuid root or via sudo !
It is not checked for the necessary degree of hacker safety.

Consider to put all authorized users into group "floppy", to chgrp the
device file to that group and to disallow w-access to others.


A possible source of problems are hald or other automounters. 
If you can spot a process "hald-addon-storage" with the address of
your desired drive, then consider to kill it.

If you cannot get rid of the automounter that easily, try whether it helps
to always load the drive tray manually before starting a write run of
xorriso. Wait until the drive light is off.
Better try to unmount an eventually mounted media before a write run.


Besides true optical drives, xorriso can also address disk files as input or
output drives. By default paths to files under /dev are accepted only if the
device represents a real optical drive. Other device files may be addressed
by prepending "stdio:" to the path.
Like:
    xorriso -dev stdio:/dev/sdb ...more arguments...
This rule may be changed by xorriso option -drive_class.
Prefix "mmc:" causes a path to be accepted only if it is a real optical drive
which is accessible by generic SCSI/MMC commands.


                              Testing

We are quite sure that libisofs produces accurate representations of the disk
files. This opinion is founded on a lot of test burns and checks by a little
test program which compares files from the mounted image with the orignals
on disk. It uses the normal POSIX filesystem calls, i.e. no libburnia stuff.

This program is not installed systemwide but stays in the installation
directory of the xorriso tarball as  test/compare_file . Usually it is
run as -exec payload of a find command. It demands at least three arguments:
The path of the first file to compare, the prefix1 to be cut off from path
and the prefix2 which gets prepended afterwards to obtain the path of the
second file to compare.
As further argument there can be -no_ctime which suppresses the comparison
of ctime date stamps.
The exit value is 0 if no difference was detected, non-0 else.

Example: After
   xorriso ... -pathspecs on -add /=/original/dir -- -commit_eject all
   mount /media/dvd
   cd test
compare tree /media/dvd with tree /original/dir :
   find /original/dir -exec ./compare_file '{}' /original/dir /media/dvd ';' \
   | less
and vice versa:
   find /media/dvd -exec ./compare_file '{}' /media/dvd /original/dir ';' \
   | less


                             File Formats

                             Sector Maps

Sector maps describe the valid and invalid blocks on a media or a disk copy of
a media. xorriso creates and reads these file with its option -check_media.

The file begins with 32 bytes of cleartext of which the last one is a
newline character. The first 25 say "xorriso sector bitmap v2 ", the
remaining six characters give the size of the info text as decimal number.
This number of bytes follows the first 32 and will not be interpreted
by xorriso. They are rather to inform a human reader about the media type
and its track layout.
After the info text there are two 4 byte signed integers, most significant
byte first. The first one, N, gives the number of bits in the following bitmap
and the second number S gives the number of 2 KiB blocks governed by a single
bit in the map. Then come the bits in form of 8-bit bytes.
Data block M is covered by bit B=M/S in the map, bit number B is stored in
byte B/8 as bit B%8. A valid readable data block has its bit set to 1.

                             Checksum Tags

Checksum tags are data blocks inside an ISO 9660 image which do not belong to
any file but rather tell the MD5 of a certain range of data blocks.

The superblock checksum tag is written after the ECMA-119 volume descriptors.
The tree checksum tag is written after the ECMA-119 directory entries.
The session checksum tag is written after all payload including the checksum
array. (Then follows eventual padding.)

The tags are single lines of printable text, padded by 0 bytes. They have
the following format:

 Tag_id pos=# range_start=# range_size=# [session_start|next=#] md5=# self=#\n

Parameters md5= and self= are 32 digit hex, the others are decimal numbers.

Tag_id distinguishes the following tag types
  "libisofs_rlsb32_checksum_tag_v1"     Relocated 64 kB superblock tag
  "libisofs_sb_checksum_tag_v1"         Superblock tag
  "libisofs_tree_checksum_tag_v1"       Directory tree tag
  "libisofs_checksum_tag_v1"            Session end tag

A relocated superblock may appear at LBA 0 of an image which was produced for
being stored in a disk file or on overwriteable media (e.g. DVD+R, BD-RE).
xorriso records the first session at LBA 32. An eventual follow-up session
begins at the next block address which is divisible by 32 and higher than the
address of the previous session's end tag. Normally no session starts after the
address given by relocated superblock parameter session_start=.
Session oriented media like CD-R[W], DVD+R, BD-R will have no relocated
superblock but rather bear a table-of-content on media level.

A tag is valid if pos= tells its own block address and self= tells its own MD5
up to the last hex digit of md5=. range_start= tells the first block that is
covered by md5=, range_size= tells the number of blocks covered by md5=.
Relocated superblocks tell the block address of their session by session_start=.
Superblock and tree tag tell the block address of the next tag by next=.
The newline character at the end is mandatory.


                             libisoburn

xorriso is based on libisofs which does ISO 9600 filesystem aspects and on
libburn which does the input and output aspects. Parts of this foundation
are accessed via libisoburn, which is closely related to xorriso.

libisoburn provides two services:
- Encapsulation of coordination between libisofs and libburn.
- Emulation of ISO 9660 multi-session on overwriteable media
  or random access files.

The sourcecode of all three libraries is included in the xorriso standalone
tarball. It is compiled with xorriso and linked statically.
But you may as well get and install releases of libburn and libisofs, in order
to be able to install a release of libisoburn which produces libisoburn.so.1
and a matching dynamically linked xorriso binary.
This binary is leaner but depends on properly installed libraries of suitable
revision.

Dynamic library and compile time header requirements for libisoburn-0.5.0 :
- libburn.so.4  , version libburn-0.7.6 or higher
- libisofs.so.6 , version libisofs-0.6.28 or higher
libisoburn and xorriso will not start with libraries which are older than their
headers seen at compile time. So compile in the oldest possible installation
setup unless you have reason to enforce a newer bug fix level.

Standalone xorriso has less runtime dependencies and can be moved more freely.


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    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 3 or later
    as published by the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

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    GNU xorriso is feature-wise equivalent to the dynamic compilation of
    libburnia libraries and libburnia program xorriso.
    It restricts itself to a technical form where the legal commitments of the
    libburnia project and the legal intentions of FSF match completely.

    Libburnia project is committed to provide support for this copy in the same
    way as for its own software releases. It is further committed to keep its
    own licenses open for obtaining future copies under GPLv2+.

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libburnia program xorriso is based on and sub project of:
libburnia-project.org
By Mario Danic           <mario.danic@gmail.com>,  libburn, libisofs
   Vreixo Formoso        <metalpain2002@yahoo.es>, libisofs, libisoburn
   Thomas Schmitt        <scdbackup@gmx.net>,      libburn, libisofs,
                                                   libisoburn, xorriso
Copyright (C) 2006-2010 Mario Danic, Vreixo Formoso, Thomas Schmitt.

libburnia-project.org is inspired by and in libburn still containing parts
of old
Libburn. By Derek Foreman <derek@signalmarketing.com> and
            Ben Jansens <xor@orodu.net>
Copyright (C) 2002-2006  Derek Foreman and Ben Jansens
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This text itself is
Copyright (c) 2007 - 2010 Thomas Schmitt <scdbackup@gmx.net>
and is freely distributable.
It shall only be modified in sync with the technical properties of xorriso.
If you make use of the license to derive modified versions of xorriso
then you are entitled to modify this text under that same license.