legacy/libburn/branches/ZeroFourZero/cdrskin/wiki_plain.txt

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                       cdrskin Wiki - plain text copy
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[[Image(source:/libburn/trunk/cdrskin/doener_150x200_tr.png)]] [http://en.wikipedia.org/wiki/D%C3%B6ner_kebab Doener]

'''cdrskin is the cdrecord compatibility middleware of libburn.'''

Its paragon, cdrecord, is a powerful GPL'ed burn program included in Joerg
Schilling's cdrtools. cdrskin strives to be a second source for the services
traditionally provided by cdrecord. Currently it does CD-R and CD-RW this way.
Overwriteable media DVD-RAM, DVD+RW and DVD-RW are handled differently than 
with cdrecord-ProDVD in order to offer TAO-like single track recording.
Sequential DVD-R[W] and DVD+R are handled like CD-R[W] with TAO and
multi-session. Additionally cdrskin offers cdrecord-ProDVD-like mode DAO
with DVD-R[W].

cdrskin does not contain any bytes copied from cdrecord's sources.
Many bytes have been copied from the message output of cdrecord
runs, though. The most comprehensive technical overview of cdrskin
can be found in [http://libburnia-project.org/browser/libburn/trunk/cdrskin/README?format=txt cdrskin/README].

About libburn API for burning CD and DVD: http://api.libburnia-project.org

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For dual layer DVD types see the advice to use dvd+rw-tools at
the end of this text.

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About the command line options of cdrskin:

They are described in detail in [http://scdbackup.sourceforge.net/man_1_cdrskin_devel.html#OPTIONS section OPTIONS] of
[http://scdbackup.sourceforge.net/man_1_cdrskin_devel.html man cdrskin]

There are two families of options: cdrecord-compatible ones and options
which are specific to cdrskin. The latter are mostly used to configure
cdrskin for its task to emulate cdrecord. There are some, nevertheless,
which provide rather exotic unique features of cdrskin.

The cdrecord-compatible options are listed in the output of
{{{
cdrskin -help
}}}
where the option "help" has *one* dash. Online: [http://scdbackup.sourceforge.net/cdrskin_help_devel cdrskin -help]

For these options you may expect program behavior that is roughly the
same as described in original  man cdrecord . 

Online: http://cdrecord.berlios.de/old/private/man/cdrecord-2.0.html

The cdrskin-specific options are listed by
{{{
cdrskin --help
}}}
where the option "help" has *two* dashes. Online: [http://scdbackup.sourceforge.net/cdrskin__help_devel cdrskin --help]

Some are very experimental and should only be
used in coordination with the libburnia developer team.
Some are of general user interest, though:

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--devices allows the sysadmin to scan the system for possible drives
and displays their detected properties.
The drives are listed one per line, with fields:
libburn-drive-number, sysadmin-device-file, permissions, vendor, type
{{{
0  dev='/dev/sr0'  rwrw-- :  'HL-DT-ST'  'DVDRAM GSA-4082B'
}}}
This feature is valuable since cdrskin -scanbus will not give you
the device file name and its current permissions.
cdrskin will accept of course the proposed dev= option as address
for any usage of the drive.

Different from cdrecord, cdrskin is intended to be run without special
privileges, i.e. no superuser setuid. It is intended that the sysadmin
controls drive accessability by rw-permissions of the drive rather than
by x-permission of the burn binary. To be usable with cdrskin, the drive
has to offer both, r- and w-permission.

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cdrskin does not only read from and write to optical drives which comply
to the MMC standard but also does the same with regular files or block
devices other than optical drives.

Because the power to alter a disk file might be a bad surprise for a
traditional user of cdrecord, it is necessary to give option
--allow_emulated_drives before an emulated drive may be addressed.
Eventually one of the startup files would be a good place for it.
See man page, section FILES.

The addresses of emulated drives begin with the prefix "stdio:".
{{{
dev=stdio:/tmp/pseudo_drive
dev=stdio:/dev/usbstick
}}}

Regular files and block devices behave much like DVD-RAM.
  
Other file types may be valid targets for write-only operations.
This includes standard output, named pipes, character devices
{{{
dev=stdio:/dev/fd/1
dev=stdio:/tmp/named_pipe
dev=stdio:/dev/ptyxy
}}}

These files behave much like blank DVD-R.

All files used as pseudo-drives have to offer rw-permission.


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The DVD capabilities of cdrskin differ from those of cdrecord-ProDVD. cdrskin
offers TAO-like multi-session with DVD-R[W], DVD+R and TAO-like single session
with overwriteable DVD media. It also offers DAO on DVD-R[W] which is probably
the same as the traditional cdrecord-ProDVD write mode.

Non-cdrecord blank mode blank=format_overwrite brings a DVD-RW
disc from its initial profile "Sequential Recording" into profile state
"Restricted Overwrite".
{{{
cdrskin dev=/dev/sr0 -v blank=format_overwrite
}}}

DVD-RAM, DVD+RW and overwriteable DVD-RW appear to cdrskin as blank media
which are capable of taking only a single track. This track may be positioned
on a 32KiB aligned address, though.
{{{
cdrskin ... write_start_address=2412m ...
}}}

Non-cdrecord blank mode blank=deformat_sequential brings an overwriteable
DVD-RW back into state "Sequential Recording" with the capability of doing
multi-session, if the drive is capable of "Incremental Streaming"
(MMC feature 21h).

Used sequential DVD-RW media may be blanked by blank=fast or blank=all which
normally both do full blanking. Thus sequential DVD-RW behave much like large
CD-RW with possibly more than 99 tracks.
  
blank=deformat_sequential does minimal blanking of DVD-RW which usually yields
media incapable of "Incremental Streaming".

Option --prodvd_cli_compatible activates blank=fast and blank=all for
overwriteable DVD-RW which normally ignore those two options. It also makes
option -multi tolerable with media and write modes which are not suitable for
multi-session. (The default behavior of cdrskin deems me to be preferrable.)

Option --grow_overwriteable_iso gives cdrskin ISO pseudo-multi-session
capabilities on DVD-RAM and DVD+RW similar to growisofs.
Associated options blank=, -multi, -msinfo and -toc are available in this case.
They either pretend a blank media (if there is no ISO 9660 image) or appendable
media with a single session and track on it. blank= invalidates ISO images.


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assert_write_lba=<lba> allows to ensure that the start block address which
was used with the formatter program (e.g. mkisofs -C) matches the start block
address which will be used by the upcoming burn.

E.g. cdrskin aborts with an error message if 
{{{
assert_write_lba=0
}}}
is given but an appendable media is to be burned which would start at
block 68432.


An ISO-9660 file system image must be prepared according to a particular
block address on media. If the prepared address and the real address on media
do not match then the filesystem will not be mountable or may even cause system
trouble.

A sequential archive format like afio or star will not necessarily need such
a coordination of addresses. It might nevertheless be confusing to a reader
if the archive does not start at block 0.

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fifo_start_at=<num> is a throughput enhancer for unsteady data streams
like they are produced by a compressing archiver program when piping to
CD on-the-fly. It makes better use of the general property of a FIFO 
buffer to transport surplus bandwidth into the future. Yep. A time machine.
One-way, i fear.

FIFO originally was introduced by cdrecord's author Joerg Schilling in order
to protect mediocre burner hardware from suffering buffer underruns
and thus producing misburns (at 1x speed on CD-R media at the price of a
DVD-RAM nowadays). This purpose would not justify a fifo any more -
given the limited life time of burners and the seamless underrun protection
of contemporary consumer drives.

With an unsteady data stream the task of the buffer is to soak up peak 
performance and to release it steadily at the drive's maximum speed.
The larger the buffer the more reserves can be built up and the longer
input drought can be compensated.

Original cdrecord has the historical property, though, to first wait until
the buffer is completely filled. Best practice for fighting drive
underruns, of course.
With a very fat fs=# buffer (128 MB for 12x CD is not unrealistic) this
can cause a big delay until burning finally starts and takes its due time.

fifo_start_at=<num> makes cdrskin start burning after the given number of bytes
is read rather than waiting for the FIFO to be completely full resp. the data
stream to end. It risks a few drive buffer underruns at the beginning of burn
- but modern drives stand this.

Usage examples:
{{{
cdrskin ...  fs=128m  fifo_start_at=20m  ...
cdrskin ...  fifo_start_at=0  ...
}}}

Note: no FIFO can give you better average throughput than the average
throughput of the data source and the throughput of the burner.
It can be used, though, to bring the effective throughput very close
to the theoretical limit. Especially with high speed media.

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--no_rc allows you to surely ban influence from systemwide or user specific
default settings of cdrskin. Possible locations for such settings:

/etc/default/cdrskin

/etc/opt/cdrskin/rc

/etc/cdrskin/cdrskin.conf

$HOME/.cdrskinrc

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dev_translation=<sep><from><sep><to> may be needed to foist cdrskin to
frontend programs of cdrecord which do *not* ask cdrecord -scanbus but
which make own assumptions and guesses about cdrecord's device addresses.

Normally, cdrskin understands all addresses which are suitable for cdrecord
under Linux. See cdrskin/README, "Pseudo-SCSI Adresses".
This option is mainly for (yet unknown) exotic configurations or very
stubborn frontend programs.

If a frontend refuses to work with cdrskin, look into the error protocol
of that frontend, look at the output of a run of cdrskin --devices and give
cdrskin the necessary hint.
Example: Your frontend insists in using "0,0,0" and --devices reported 
dev='/dev/hdc' resp. cdrskin dev=ATA -scanbus reported "1,0,0" then this
would be the appropriate translation:
{{{
dev_translation=+0,0,0+/dev/hdc
}}}
The "+" character is a separator to be choosen by you.
Currently i am not aware of the need to choose any other than "+"
unless you get playful with custom translations like
{{{
dev_translation=-"cd+dvd"-1,0,0
}}}
See http://scdbackup.sourceforge.net/k3b_on_cdrskin.html
for an illustrated example with K3b 0.10 .

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DVD advise:

For burning of DVD media other than DVD-RAM, DVD+RW, DVD+R, DVD-RW, DVD-R,
the cdrskin project currently advises to use Andy Polyakov's dvd+rw-tools
which despite their historic name are capable of all the media above 
and also do dual layer and even BD discs. 

http://fy.chalmers.se/~appro/linux/DVD+RW/tools

They are not compatible or related to cdrecord resp. cdrecord-ProDVD
(now obsoleted by original source cdrtools cdrecord with identical
capabilities besides the license key).

A special feature of dvd+rw-tools is growing of ISO-9660 filesystems on
overwriteable media. This is not the same as multi-session writing of cdrskin
with CD media, but retrieves additional information from the existing ISO
image and finally manipulates the start sectors of this existing image.

So, inspired by growisofs, cdrskin can offer DVD multi-session not only with
sequential DVD-R[W] and with DVD+R, but also with DVD-RAM, DVD+RW and
even regular disk files or block devices other than CD/DVD writers.
This is enabled by option --grow_overwriteable_iso.

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