config root man

.\" Copyright (c) 1996
.\"	Julian Elischer <julian@FreeBSD.org>.  All rights reserved.
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.\" $FreeBSD: release/9.1.0/share/man/man4/cd.4 231718 2012-02-15 01:39:04Z gjb $
.\"
.Dd February 8, 2012
.Dt CD 4
.Os
.Sh NAME
.Nm cd
.Nd SCSI CD-ROM driver
.Sh SYNOPSIS
.Cd device cd
.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 ada 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 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 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 the header file
.In sys/disklabel.h .
.It Dv CDIOCCAPABILITY
.Pq Li "struct ioc_capability"
Retrieve information from the drive on what features it supports.
The information is returned in the following structure:
.Bd -literal -offset indent
struct ioc_capability {
	u_long	play_function;
#define CDDOPLAYTRK	0x00000001
	/* Can play tracks/index */
#define	CDDOPLAYMSF	0x00000002
	/* Can play msf to msf */
#define	CDDOPLAYBLOCKS	0x00000004
	/* Can play range of blocks */
#define	CDDOPAUSE	0x00000100
	/* Output can be paused */
#define	CDDORESUME	0x00000200
	/* Output can be resumed */
#define	CDDORESET	0x00000400
	/* Drive can be completely reset */
#define	CDDOSTART	0x00000800
	/* Audio can be started */
#define CDDOSTOP	0x00001000
	/* Audio can be stopped */
#define CDDOPITCH	0x00002000
	/* Audio pitch can be changed */

	u_long	routing_function;
#define CDREADVOLUME	0x00000001
	/* Volume settings can be read */
#define CDSETVOLUME	0x00000002
	/* Volume settings can be set */
#define	CDSETMONO	0x00000100
	/* Output can be set to mono */
#define CDSETSTEREO	0x00000200
	/* Output can be set to stereo (def) */
#define	CDSETLEFT	0x00000400
	/* Output can be set to left only */
#define	CDSETRIGHT	0x00000800
	/* Output can be set to right only */
#define	CDSETMUTE	0x00001000
	/* Output can be muted */
#define CDSETPATCH	0x00008000
	/* Direct routing control allowed */

	u_long	special_function;
#define	CDDOEJECT	0x00000001
	/* The tray can be opened */
#define	CDDOCLOSE	0x00000002
	/* The tray can be closed */
#define	CDDOLOCK	0x00000004
	/* The tray can be locked */
#define CDREADHEADER	0x00000100
	/* Can read Table of Contents */
#define	CDREADENTRIES	0x00000200
	/* Can read TOC Entries */
#define	CDREADSUBQ	0x00000200
	/* Can read Subchannel info */
#define CDREADRW	0x00000400
	/* Can read subcodes R-W */
#define	CDHASDEBUG	0x00004000
	/* The tray has dynamic debugging */
};
.Ed
.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.
.It Dv CDIOCPITCH
.Pq Li "struct ioc_pitch"
For drives that support it, this command instructs the drive to play
the audio at a faster or slower rate than normal.
Values of
.Li speed
between -32767 and -1 result in slower playback; a zero value
indicates normal speed; and values from 1 to 32767 give faster
playback.
Drives with less than 16 bits of resolution will silently
ignore less-significant bits.
The structure is defined thusly:
.Bd -literal -offset indent
struct	ioc_pitch
{
	short	speed;
};
.Ed
.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.
As 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 and kernel tunable 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/kernel tunable 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 SYSCTL VARIABLES
The following variables are available as both
.Xr sysctl 8
variables and
.Xr loader 8
tunables:
.Bl -tag -width 12
.It kern.cam.cd.retry_count
.Pp
This variable determines how many times the
.Nm
driver will retry a READ or WRITE command.
This does not affect the number of retries used during probe time or for
the
.Nm
driver dump routine.
This value currently defaults to 4.
.It kern.cam.cd.%d.minimum_cmd_size
.Pp
The
.Nm
driver attempts to automatically determine whether the drive it is talking
to supports 6 byte or 10 byte MODE SENSE/MODE SELECT operations.
Many
.Tn SCSI
drives only support 6 byte commands, and
.Tn ATAPI
drives only support 10 byte commands.
The
.Nm
driver first attempts to determine whether the protocol in use typically
supports 6 byte commands by issuing a CAM Path Inquiry CCB.
It will then default to 6 byte or 10 byte commands as appropriate.
After that, the
.Nm
driver defaults to using 6 byte commands (assuming the protocol the drive
speaks claims to support 6 byte commands), until one fails with a
.Tn SCSI
ILLEGAL REQUEST error.
Then it tries the 10 byte version of the command to
see if that works instead.
Users can change the default via per-drive
sysctl variables and loader tunables.
Where
.Dq %d
is the unit number of the drive in question.
Valid minimum command sizes
are 6 and 10.
Any value above 6 will be rounded to 10, and any value below
6 will be rounded to 6.
.It kern.cam.cd.changer.min_busy_seconds
.It kern.cam.cd.changer.max_busy_seconds
.Pp
Tune how long individual LUNs are 'locked' for I/O operations to
optimize changer operation.
See CHANGER OPERATION section for information on how to use these items.
.El
.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 cam 4 ,
.Xr da 4 ,
.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.