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Cdrskin.md
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Cdrskin.md
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[Doener](http://en.wikipedia.org/wiki/Doner_kebab)
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### cdrskin is the cdrecord compatibility middleware of libburn and part of its release tarball.
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Its paragon, cdrecord, is a powerful GPL'ed burn program included in Joerg
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Schilling's cdrtools. cdrskin strives to be a second source for the services
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traditionally provided by cdrecord. Currently it does CD-R and CD-RW this way.
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Overwriteable media DVD-RAM, DVD+RW, DVD-RW, and BD-RE are handled differently
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than with cdrecord-ProDVD in order to offer TAO-like single track recording.
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Sequential DVD-R[W], DVD+R, DVD+R DL, BD-R are handled like CD-R[W] with TAO
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and multi-session. Additionally cdrskin offers cdrecord-ProDVD-like mode DAO
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with DVD-R[W].
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cdrskin does not contain any bytes copied from cdrecord's sources.
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Many bytes have been copied from the message output of cdrecord
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runs, though. The most comprehensive technical overview of cdrskin
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can be found in
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[cdrskin/README](https://dev.lovelyhq.com/libburnia/libburn/raw/HEAD/cdrskin/README).
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FIXME: About libburn API for burning CD, DVD, and BD: http://api.libburnia-project.org
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--------------------------------------------------------------------------
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About the command line options of cdrskin:
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They are described in detail in [section OPTIONS](http://scdbackup.sourceforge.net/man_1_cdrskin_devel.html#OPTIONS) of
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[man cdrskin](http://scdbackup.sourceforge.net/man_1_cdrskin_devel.html)
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There are two families of options: cdrecord-compatible ones and options
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which are specific to cdrskin. The latter are mostly used to configure
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cdrskin for its task to emulate cdrecord. There are some, nevertheless,
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which provide rather exotic unique features of cdrskin.
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The cdrecord-compatible options are listed in the output of
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```
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cdrskin -help
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```
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where the option "help" has *one* dash. Online: [cdrskin -help](http://scdbackup.sourceforge.net/cdrskin_help)
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For these options you may expect program behavior that is roughly the
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same as described in original man cdrecord .
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Online: http://cdrtools.sourceforge.net/private/man/cdrecord/cdrecord.1.html
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The cdrskin-specific options are listed by
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```
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cdrskin --help
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```
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where the option "help" has *two* dashes. Online: [cdrskin --help](http://scdbackup.sourceforge.net/cdrskin__help)
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Some are very experimental and should only be
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used in coordination with the libburnia developer team.
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Some are of general user interest, though:
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--------------------------------------------------------------------------
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`--devices` can be used by the sysadmin to scan the system for possible drives
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and displays their detected properties.
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The drives are listed one per line, with fields:
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libburn-drive-number, sysadmin-device-file, permissions, vendor, type
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```
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0 dev='/dev/sr0' rwrw-- : 'HL-DT-ST' 'DVDRAM GSA-4082B'
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````
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This feature is valuable since cdrskin `-scanbus` will not give you
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the device file name and its current permissions.
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cdrskin will accept of course the proposed `dev=` option as address
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for any usage of the drive.
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Different from cdrecord, cdrskin is intended to be run without special
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privileges, i.e. no superuser setuid. It is intended that the sysadmin
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controls drive accessability by rw-permissions of the drive rather than
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by x-permission of the burn binary. To be usable with cdrskin, the drive
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has to offer both, r- and w-permission.
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--------------------------------------------------------------------------
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`blank=as_needed` applies the suitable blanking or formatting to make
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any supported type of media ready for writing from scratch.
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If this is not possible, e.g. because the media is written and not
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re-usable, then the program run fails.
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Option `blank=` offers several specialized blanking and formatting types,
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which one may use for particular purposes on DVD-RW, DVD-RAM and BD-RE.
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(See also below: `blank=format_overwrite`)
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The drive offers a list of possible formats by cdrskin option `--list_formats`.
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One should aquire MMC background information before making use of them.
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--------------------------------------------------------------------------
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cdrskin does not only read from and write to optical drives which comply
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to the MMC standard but also does the same with regular files or block
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devices other than optical drives.
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Because the power to alter a disk file might be a bad surprise for a
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traditional user of cdrecord, it is necessary to give option
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`--allow_emulated_drives` before an emulated drive may be addressed.
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Eventually one of the startup files would be a good place for it.
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See man page, section FILES.
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The addresses of emulated drives begin with the prefix "stdio:".
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```
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dev=stdio:/tmp/pseudo_drive
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dev=stdio:/dev/usbstick
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```
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Regular files and block devices behave much like DVD-RAM.
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Other file types may be valid targets for write-only operations.
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This includes standard output, named pipes, character devices
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```
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dev=stdio:/dev/fd/1
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dev=stdio:/tmp/named_pipe
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dev=stdio:/dev/ptyxy
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```
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These files behave much like blank DVD-R.
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All files used as pseudo-drives have to offer rw-permission.
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--------------------------------------------------------------------------
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The DVD capabilities of cdrskin differ from those of cdrecord-ProDVD. cdrskin
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offers TAO-like multi-session with DVD-R[W], DVD+R[ DL] and TAO-like single
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session with overwriteable DVD media. It also offers DAO on DVD-R[W] which is
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probably the same as the traditional cdrecord-ProDVD write mode.
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Non-cdrecord blank mode `blank=format_overwrite` brings a DVD-RW
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disc from its initial profile "Sequential Recording" into profile state
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"Restricted Overwrite".
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```
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cdrskin dev=/dev/sr0 -v blank=format_overwrite
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```
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DVD-RAM, DVD+RW, BD-RE and overwriteable DVD-RW appear to cdrskin as blank
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media which are capable of taking only a single track. This track may be
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positioned on a 32KiB aligned address, though.
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```
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cdrskin ... write_start_address=2412m ...
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```
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Non-cdrecord blank mode `blank=deformat_sequential` brings an overwriteable
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DVD-RW back into state "Sequential Recording" with the capability of doing
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multi-session.
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Used sequential DVD-RW media may be blanked by `blank=fast` or `blank=all` which
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normally both do full blanking. Thus sequential DVD-RW behave much like large
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CD-RW with possibly more than 99 tracks.
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`blank=deformat_sequential` does minimal blanking of DVD-RW which usually yields
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media incapable of "Incremental Streaming".
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Option `--prodvd_cli_compatible` activates `blank=fast` and `blank=all` for
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overwriteable DVD-RW which normally ignore those two options. It also makes
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option `-multi` tolerable with media and write modes which are not suitable for
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multi-session. (The default behavior of cdrskin deems me to be preferrable.)
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Option `--grow_overwriteable_iso` gives cdrskin ISO pseudo-multi-session
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capabilities on DVD-RAM, DVD+RW, BD-RE similar to growisofs.
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Associated options `blank=`, `-multi`, `-msinfo` and `-toc` are available
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in this case.
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They either pretend a blank media (if there is no ISO 9660 image) or appendable
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media with a single session and track on it. `blank=` invalidates ISO images.
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--------------------------------------------------------------------------
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`assert_write_lba=<lba>` ensures that the start block address which
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was used with the formatter program (e.g. `mkisofs -C`) matches the start block
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address which will be used by the upcoming burn.
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E.g. cdrskin aborts with an error message if
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```
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assert_write_lba=0
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```
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is given but an appendable media is to be burned which would start at
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block 68432.
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An ISO-9660 file system image must be prepared according to a particular
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block address on media. If the prepared address and the real address on media
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do not match then the filesystem will not be mountable or may even cause system
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trouble.
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A sequential archive format like afio or star will not necessarily need such
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a coordination of addresses. It might nevertheless be confusing to a reader
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if the archive does not start at block 0.
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--------------------------------------------------------------------------
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`fifo_start_at=<num>` is a throughput enhancer for unsteady data streams
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like they are produced by a compressing archiver program when piping to
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CD on-the-fly. It makes better use of the general property of a FIFO
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buffer to transport surplus bandwidth into the future. Yep. A time machine.
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One-way, i fear.
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FIFO originally was introduced by cdrecord's author Joerg Schilling in order
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to protect mediocre burner hardware from suffering buffer underruns
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and thus producing misburns (at 1x speed on CD-R media at the price of a
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DVD-RAM nowadays). This purpose would not justify a fifo any more -
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given the limited life time of burners and the seamless underrun protection
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of contemporary consumer drives.
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With an unsteady data stream the task of the buffer is to soak up peak
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performance and to release it steadily at the drive's maximum speed.
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The larger the buffer the more reserves can be built up and the longer
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input drought can be compensated.
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Original cdrecord has the historical property, though, to first wait until
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the buffer is completely filled. Best practice for fighting drive
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underruns, of course.
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With a very fat `fs=#` buffer (128 MB for 12x CD is not unrealistic) this
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can cause a big delay until burning finally starts and takes its due time.
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`fifo_start_at=<num>` makes cdrskin start burning after the given number
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of bytes
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is read rather than waiting for the FIFO to be completely full resp. the data
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stream to end. It risks a few drive buffer underruns at the beginning of burn,
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but modern drives stand this.
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Usage examples:
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```
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cdrskin ... fs=128m fifo_start_at=20m ...
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cdrskin ... fifo_start_at=0 ...
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```
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Note: no FIFO can give you better average throughput than the average
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throughput of the data source and the throughput of the burner.
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It can be used, though, to bring the effective throughput very close
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to the theoretical limit. Especially with high speed media.
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--------------------------------------------------------------------------
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`--no_rc` allows you to surely ban influence from systemwide or user specific
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default settings of cdrskin. Possible locations for such settings:
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```
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/etc/default/cdrskin
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/etc/opt/cdrskin/rc
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/etc/cdrskin/cdrskin.conf
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$HOME/.cdrskinrc
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```
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--------------------------------------------------------------------------
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`dev_translation=<sep><from><sep><to`> may be needed to foist cdrskin to
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frontend programs of cdrecord which do *not* ask `cdrecord -scanbus` but
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which make own assumptions and guesses about cdrecord's device addresses.
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Normally, cdrskin understands all addresses which are suitable for cdrecord
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under Linux. See `cdrskin/README`, "Pseudo-SCSI Adresses".
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This option is mainly for (yet unknown) exotic configurations or very
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stubborn frontend programs.
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If a frontend refuses to work with cdrskin, look into the error protocol
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of that frontend, look at the output of a run of `cdrskin --devices` and give
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cdrskin the necessary hint.
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Example: Your frontend insists in using "0,0,0" and `--devices` reported
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`dev='/dev/hdc'` resp. `cdrskin dev=ATA -scanbus` reported "1,0,0" then this
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would be the appropriate translation:
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```
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dev_translation=+0,0,0+/dev/hdc
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```
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The "+" character is a separator to be choosen by you.
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Currently i am not aware of the need to choose any other than "+"
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unless you get playful with custom translations like
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```
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dev_translation=-"cd+dvd"-1,0,0
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```
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See http://scdbackup.sourceforge.net/k3b_on_cdrskin.html
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for an illustrated example with K3b 0.10 .
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--------------------------------------------------------------------------
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Advanced multi-session use cases as of dvd+rw-tools:
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A special feature of dvd+rw-tools is growing of ISO-9660 filesystems on
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overwriteable media. This is not the same as multi-session writing of cdrskin
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with CD media, but retrieves additional information from the existing ISO
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image and finally manipulates the start sectors of this existing image.
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So, inspired by growisofs, cdrskin can offer DVD multi-session not only with
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sequential DVD-R[W] and with DVD+R [DL], but also with DVD-RAM, DVD+RW, BD-RE
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and even regular disk files or block devices other than CD/DVD writers.
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This is enabled by option `--grow_overwriteable_iso`.
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The libburnia project provides an integrated ISO-9660 multi-session tool
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named [xorriso](Xorriso) which tries to go one step beyond
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growisofs. It uses [libburn](Libburn) , [libisofs](Libisofs)
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and [libisoburn](Libisoburn).
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See [man xorriso](http://scdbackup.sourceforge.net/man_1_xorriso.html).
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--------------------------------------------------------------------------
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