man/man4/cd.4

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.\"	Julian Elischer <julian@FreeBSD.org>.  All rights reserved.
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.\" $FreeBSD: src/share/man/man4/cd.4,v 1.17.2.8 2003/06/03 14:32:09 hmp Exp $
.\"
.Dd February 18, 2019
.Dt CD 4
.Os
.Sh NAME
.Nm cd
.Nd SCSI CD-ROM driver
.Sh SYNOPSIS
.Cd device cd
.Cd device cd1 at scbus0 target 4 unit 0
.Cd "options CHANGER_MIN_BUSY_SECONDS=3"
.Cd "options CHANGER_MAX_BUSY_SECONDS=11"
.Sh DESCRIPTION
The
.Nm
driver provides support for a
.Tn SCSI
.Tn CD-ROM
(Compact Disc-Read Only Memory) drive.
In an attempt to look like a regular disk, the
.Nm
driver synthesizes a partition table, with one partition covering the entire
.Tn CD-ROM .
It is possible to modify this partition table using
.Xr disklabel 8 ,
but it will only last until the
.Tn CD-ROM
is unmounted.
In general the interfaces are similar to those described by
.Xr ad 4
and
.Xr da 4 .
.Pp
As the
.Tn SCSI
adapter is probed during boot, the
.Tn SCSI
bus is scanned for devices.
Any devices found which answer as CDROM
(type 5) or WORM (type 4) type devices will be `attached' to the
.Nm
driver.
Prior to
.Fx 2.1 ,
the first device found will be attached as
.Li cd0
the next,
.Li cd1 ,
etc.
Beginning in
.Fx 2.1
it is possible to specify what cd unit a device should
come on line as; refer to
.Xr scsi 4
for details on kernel configuration.
.Pp
The
.Cd target
string is followed by the device's standard
.Tn SCSI
device ID number.
The
.Cd unit
string is followed by the Logical Unit Number
.Pq Tn LUN
of the
.Tn SCSI
device's sub-device, if any, or zero.
.Pp
The system utility
.Xr disklabel 8
may be used to read the synthesized
disk label
structure, which will contain correct figures for the size of the
.Tn CD-ROM
should that information be required.
.Sh KERNEL CONFIGURATION
Any number of
.Tn CD-ROM
devices may be attached to the system regardless of system
configuration as all resources are dynamically allocated.
.Sh IOCTLS
The following
.Xr ioctl 2
calls which apply to
.Tn SCSI
.Tn CD-ROM
drives are defined
in the header files
.In sys/cdio.h
and
.In sys/disklabel.h .
.Bl -tag -width ".Dv CDIOCREADSUBCHANNEL"
.It Dv DIOCGDINFO
.It Dv DIOCSDINFO
.Pq Li "struct disklabel"
Read or write the in-core copy of the disklabel for the
drive.
The disklabel is initialized with information
read from the scsi inquiry commands, and should be the same as
the information printed at boot.
This structure is defined in
.Xr disklabel 5 .
.It Dv CDIOCPLAYTRACKS
.Pq Li "struct ioc_play_track"
Start audio playback given a track address and length.
The structure is defined as follows:
.Bd -literal -offset indent
struct ioc_play_track
{
	u_char	start_track;
	u_char	start_index;
	u_char	end_track;
	u_char	end_index;
};
.Ed
.It Dv CDIOCPLAYBLOCKS
.Pq Li "struct ioc_play_blocks"
Start audio playback given a block address and length.
The structure is defined as follows:
.Bd -literal -offset indent
struct ioc_play_blocks
{
	int	blk;
	int	len;
};
.Ed
.It Dv CDIOCPLAYMSF
.Pq Li "struct ioc_play_msf"
Start audio playback given a `minutes-seconds-frames' address and
length.
The structure is defined as follows:
.Bd -literal -offset indent
struct ioc_play_msf
{
	u_char	start_m;
	u_char	start_s;
	u_char	start_f;
	u_char	end_m;
	u_char	end_s;
	u_char	end_f;
};
.Ed
.It Dv CDIOCREADSUBCHANNEL
.Pq Li "struct ioc_read_subchannel"
Read information from the subchannel at the location specified by this
structure:
.Bd -literal -offset indent
struct ioc_read_subchannel {
	u_char address_format;
#define CD_LBA_FORMAT	1
#define CD_MSF_FORMAT	2
	u_char data_format;
#define CD_SUBQ_DATA		0
#define CD_CURRENT_POSITION	1
#define CD_MEDIA_CATALOG	2
#define CD_TRACK_INFO		3
	u_char track;
	int	data_len;
	struct  cd_sub_channel_info *data;
};
.Ed
.It Dv CDIOREADTOCHEADER
.Pq Li "struct ioc_toc_header"
Return summary information about the table of contents for the mounted
.Tn CD-ROM .
The information is returned into the following structure:
.Bd -literal -offset indent
struct ioc_toc_header {
	u_short len;
	u_char  starting_track;
	u_char  ending_track;
};
.Ed
.It Dv CDIOREADTOCENTRYS
.Pq Li "struct ioc_read_toc_entry"
Return information from the table of contents entries mentioned.
.Pq Yes, this command name is misspelled.
The argument structure is defined as follows:
.Bd -literal -offset indent
struct ioc_read_toc_entry {
	u_char	address_format;
	u_char	starting_track;
	u_short	data_len;
	struct  cd_toc_entry *data;
};
.Ed
The requested data is written into an area of size
.Li data_len
and pointed to by
.Li data .
.It Dv CDIOCSETPATCH
.Pq Li "struct ioc_patch"
Attach various audio channels to various output channels.
The argument structure is defined thusly:
.Bd -literal -offset indent
struct ioc_patch {
	u_char	patch[4];
	/* one for each channel */
};
.Ed
.It Dv CDIOCGETVOL
.It Dv CDIOCSETVOL
.Pq Li "struct ioc_vol"
Get (set) information about the volume settings of the output channels.
The argument structure is as follows:
.Bd -literal -offset indent
struct	ioc_vol
{
	u_char	vol[4];
	/* one for each channel */
};
.Ed
.It Dv CDIOCSETMONO
Patch all output channels to all source channels.
.It Dv CDIOCSETSTEREO
Patch left source channel to the left output channel and the right
source channel to the right output channel.
.It Dv CDIOCSETMUTE
Mute output without changing the volume settings.
.It Dv CDIOCSETLEFT
.It Dv CDIOCSETRIGHT
Attach both output channels to the left (right) source channel.
.It Dv CDIOCSETDEBUG
.It Dv CDIOCCLRDEBUG
Turn on (off) debugging for the appropriate device.
.It Dv CDIOCPAUSE
.It Dv CDIOCRESUME
Pause (resume) audio play, without resetting the location of the read-head.
.It Dv CDIOCRESET
Reset the drive.
.It Dv CDIOCSTART
.It Dv CDIOCSTOP
Tell the drive to spin-up (-down) the
.Tn CD-ROM .
.It Dv CDIOCALLOW
.It Dv CDIOCPREVENT
Tell the drive to allow (prevent) manual ejection of the
.Tn CD-ROM
disc.  Not all drives support this feature.
.It Dv CDIOCEJECT
Eject the
.Tn CD-ROM .
.It Dv CDIOCCLOSE
Tell the drive to close its door and load the media.
Not all drives support this feature.
.El
.Sh NOTES
When a
.Tn CD-ROM
is changed in a drive controlled by the
.Nm
driver, then the act of changing the media will invalidate the
disklabel and information held within the kernel.
To stop corruption,
all accesses to the device will be discarded until there are no more
open file descriptors referencing the device.
During this period, all
new open attempts will be rejected.
When no more open file descriptors
reference the device, the first next open will load a new set of
parameters (including disklabel) for the drive.
.Pp
The audio code in the
.Nm
driver only support
.Tn SCSI-2
standard audio commands.
Because many
.Tn CD-ROM
manufacturers have not followed the standard, there are many
.Tn CD-ROM
drives for which audio will not work.
Some work is planned to support
some of the more common `broken'
.Tn CD-ROM
drives; however, this is not yet under way.
.Sh CHANGER OPERATION
This driver has built-in support for LUN-based CD changers.
A LUN-based CD
changer is a drive that can hold two or more CDs, but only has one CD
player mechanism.
Each CD in the drive shows up as a separate logical unit
on the
.Tn SCSI
bus.  The
.Nm
driver automatically recognizes LUN-based changers, and routes commands for
changers through an internal scheduler.
The scheduler prevents changer
"thrashing", which is caused by sending commands to different LUNs in the
changer at the same time.
.Pp
The scheduler honors minimum and maximum time
quanta that the driver will spend on a particular LUN.
The minimum time
is the guaranteed minimum amount of time that the driver will spend on a
given LUN, even if there is no outstanding I/O for that LUN.
The maximum
time is the maximum amount of time the changer will spend on a LUN if there
is outstanding I/O for another LUN.
If there is no outstanding I/O for
another LUN, the driver will allow indefinite access to a given LUN.
.Pp
The minimum and maximum time quanta are configurable via kernel options and
also via sysctl variables.
The kernel options are:
.Pp
.Bl -item -compact
.It
.Cd "options ""CHANGER_MIN_BUSY_SECONDS=3"""
.It
.Cd "options ""CHANGER_MAX_BUSY_SECONDS=11"""
.El
.Pp
The sysctl variables are:
.Pp
.Bl -item -compact
.It
.Va kern.cam.cd.changer.min_busy_seconds
.It
.Va kern.cam.cd.changer.max_busy_seconds
.El
.Pp
It is suggested that the user try experimenting with the minimum and
maximum timeouts via the sysctl variables to arrive at the proper values
for your changer.
Once you have settled on the proper timeouts for your
changer, you can then put them in your kernel config file.
.Pp
If your system does have a LUN-based changer, you may notice that the
probe messages for the various LUNs of the changer will continue to appear
while the boot process is going on.
This is normal, and is caused by the
changer scheduling code.
.Sh FILES
.Bl -tag -width /dev/cd[0-9][a-h] -compact
.It Pa /dev/cd[0-9][a-h]
raw mode
.Tn CD-ROM
devices
.El
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr da 4 ,
.Xr scsi 4 ,
.Xr disklabel 5 ,
.Xr disklabel 8 ,
.Xr cd 9
.Sh HISTORY
This
.Nm
driver is based upon the
.Nm
driver written by Julian Elischer, which appeared in
.Bx 386 0.1 .
The
CAM version of the
.Nm
driver was written by Kenneth Merry and first appeared in
.Fx 3.0 .
.Sh BUGS
The names of the structures used for the third argument to
.Fn ioctl
were poorly chosen, and a number of spelling errors have survived in
the names of the
.Fn ioctl
commands.
.Pp
There is no mechanism currently to set different minimum and maximum
timeouts for different CD changers; the timeout values set by the kernel
options or the sysctl variables apply to all LUN-based CD changers in the
system.
It is possible to implement such support, but the sysctl
implementation at least would be rather inelegant, because of the current
inability of the sysctl code to handle the addition of nodes after compile
time.
Thus, it would take one dynamically sized sysctl variable and a
userland utility to get/set the timeout values.
Implementation of separate
timeouts for different CD devices in the kernel config file would likely
require modification of
.Xr config 8
to support the two timeouts when hardwiring
.Nm
devices.