freebsd-dev/share/man/man4/worm.4

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.Dd January 27, 1996
.Dt WORM 4
.Os FreeBSD
.Sh NAME
.Nm worm
.Nd write-once (CD-R) disk driver
.Sh SYNOPSIS
.Cd disk worm0
.Cd disk worm0 target 5 lun 0
.Sh DESCRIPTION
The
.Nm worm
driver provides support for a 
.Em SCSI
write-once device, in particular for a CD-R recording device.  The
driver attempts to abstract the dirty hardware work to a common API as
good as possible.  Due to the very special nature of CD-R devices and
their handling requirements, this API applies some more constraints to
the user than those of other disk-like devices.
.Pp
A CD is usually structured into sessions and tracks.  Each track can
hold a different type of data, basically either audio information, or
CD-ROM data.  In order to record a CD-R, the device must be told which
kind of data is to be recorded, at which speed, etc.  Once all tracks
of a session have been written, the medium must finally be
.Em fixated
which basically means that the table of contents will be written, and
the session is marked as usable.  Optionally, a new session can be
enabled at this time, or the disk can be entirely closed to prevent
further writing.
.Pp
One particular feature of all existing CD-R recorders is that they
require a constant data stream while the write channel is open.  This
usually requires some precautions like using a multiple-buffering
filter to read the data from the disk, and/or running at real-time
priority.
.Pp
There is no official standard for CD-R devices, so every vendor seems
to implement his own set of controlling commands.  Some vendors use
rather similar command sets, while other devices behave entirely
different.  The driver has builtin knowledge about the odds and ends
of some devices, which must then be selected first at run-time in
order to make the driver operational at all.  This builtin knowledge
will be replaced by a loadable module scenario in the future.
.Pp
Due to the requirement of adjusting several parameters before actually
being able to write some data to the CD-R, and due to the tight timing
requirements when writing data, the driver distinguishes two different
operation modes.  When opening a file descriptor for a device belonging
to the
.Nm
driver without write access, the driver does not enforce the tight
timing that is needed to write data to the CD-R, but it allows for
sending
.Xr ioctl 2
commands to adjust parameters.  Any number of ioctls can be performed
on the device as long as the required sequence of actions is being
maintained.  The first thing that must be done is to select a set of
quirks for the actual device.  Then, the per-session parameters must
be specified.  Each track requires a set of per-track parameters
finally.
.Pp
Once all preparations have been done, the device can be opened with
write intent, at which point the driver starts to activate the
time-critical handling, and is expecting any number of
.Xr write 2
system calls that is required in order to transfer all the data to the
device.  Failure in providing these data in a timely fashion will render
the current medium unusable.  The device-specific sequence for telling
that the current track is finally complete will be issued to the device
when calling
.Xr close 2
on the file descriptor that has been used to write the data.
.Pp
After this happened, things are no longer time-critical.  Any number of
further tracks can be written to the device.  Finally, the session must
be fixated by another ioctl.
.Sh IOCTLS
The following 
.Xr ioctl 2
calls apply to CD-R devices.  Their declaration can be found in the
header file
.Pa <sys/wormio.h> .
.Bl -tag -width WORMIOCQUIRKSELECT
.It Dv WORMIOCQUIRKSELECT
Select the set of quirk functions to use for this device.  This is the
only allowed action on a virgin device after booting.  The argument
structure takes a vendor and a model string, which are matched against
the vendor and model strings of all quirk records that have been
registered with the driver.  Currently, the only known quirks must
have been statically compiled into the driver.
.Pp
If the driver fails to match the vendor and model string against any
known quirk record, the system call returns with an error, and the
variable
.Va errno
will be set to
.Er EINVAL .
The system call argument is a pointer to a
.Dv struct wormio_quirk_select .
.It Dv WORMIOCPREPDISK
This command selects several session-wide parameters in the driver.
The argument structure,
.Dv struct wormio_prepare_disk
takes two integer values,
.Dv dummy ,
and
.Dv speed .
By setting
.Dv dummy
to 1, the drive will be told to simulate all actions, without actually
turning on the laser.  It is mainly used to test the environment
whether it could cope with the timing constraints, without risking a
damaged medium.  The parameter
.Dv speed
is device-dependent, where a speed value of one generally applies to
audio disks, and a speed value of 2 (or more) is used for recording
data.
.It Dv WORMIOCPREPTRACK
The two parameters
.Dv audio
and
.Dv preemp
are being passed as arguments in a
.Dv struct wormio_prepare_track .
Both are Boolean, i.e. can be either 0 or 1.  If
.Dv audio
is set to 1, the next track will be recorded in audio format, with
2352 bytes per block.  If
.Dv preemp
is also set to 1, the audio data are assumed to be recorded with
preemphasis.  If
.Dv audio
is 0, CD-ROM data with a block length of 2048 bytes are about to be
written next.
.It Dv WORMIOCFIXATION
This closes the current session.  The argument is a pointer to
.Dv struct wormio_fixation ,
with the elements
.Dv toc_type ,
an integer between 0 and 4, describing the table-of-contents type.  See
.Xr wormcontrol 8
for a list of useful values.  Optionally, setting the field
.Dv onp
to 1 will cause the next session being opened, so further recording
can be performed into the remaining space.  If
.Dv onp
is 0, the disk will be closed once and for all.
.El
Specifying wrong argument values to the above ioctl command will cause
the driver to return an error condition with
.Va errno
set to
.Er EINVAL .
Any attempt to perform something else then selecting a quirks record
on a device where this has not been done yet will return an error of
.Er ENXIO .
.Pp
In addition, the 
.Xr scsi 4
general ioctls may be used with the 
.Nm
driver, but only against the control device.
.Sh BUGS
The driver is considered beta quality.  There's still a lot of
polishing required.
.Pp
Preparing the driver for a CD-R from another vendor will require you
to understand the source code, be used to the SCSI-2 specification,
hold a copy of the vendor's SCSI reference manual on your desk, and
have a lot of patience and CD-R's.
.Pp
The driver should include all the functionality of the
.Xr cd 4
driver.  No strategy for implementing this kind of interaction has
been designed yet.
.Pp
The first
.Em Unit Attention
conditition after a media change is often not yet caught, although
the driver was designed to catch it.  This can royally screw a user
of the driver, thus make sure to manually catch it before actually
starting a burn.  This can be done for example with a dummy
.Em Test Unit Ready
command:
.Bd -literal
scsi -f /dev/rworm0.ctl -c "0 0 0 0 0 0" >/dev/null 2>&1
.Ed
.Sh FILES
.Bl -tag -width /dev/rworm[0-9].ctl -compact
.It Pa /dev/rworm[0-9]
device for ioctl's and to write a CD-R
.It Pa /dev/rworm[0-9].ctl
the control device, as being used by
.Xr scsi 8
.El
.Sh DIAGNOSTICS
See above.
.Sh SEE ALSO
.Xr close 2 ,
.Xr ioctl 2 ,
.Xr open 2 ,
.Xr write 2 ,
.Xr cd 4 ,
.Xr scsi 4 ,
.Xr scsi 8 ,
.Xr wormcontrol 8
.Sh AUTHORS
The first skeleton for a
.Nm
driver has been written by Peter Dufault in May, 1995.  The driver has
then been improved and made actually usable at all by
.ie t J\(:org Wunsch
.el Joerg Wunsch
in January, 1996.
.Sh HISTORY
The
.Nm
driver appeared in
.Fx 2.1 .