CD(4) - Device Drivers Manual #
CD(4) - Device Drivers Manual
NAME #
cd - ATAPI and SCSI CD-ROM driver
SYNOPSIS #
cd* at scsibus? #cd0 at scsibus0 target 6 lun 0 (fixed-configuration example)
DESCRIPTION #
The cd driver provides support for ATAPI and SCSI CD-ROM (Compact Disc Read-Only Memory) drives, via scsibus(4). In an attempt to look like a regular disk, the cd driver synthesizes a partition table, with one partition covering the entire CD-ROM. It is possible to modify this partition table using disklabel(8), but it will only last until the CD-ROM is unmounted. In general the interfaces are similar to those described by wd(4) and sd(4).
As the SCSI adapter is probed during boot, the SCSI bus is scanned for devices. Any devices found which answer as “Read-only” and “removable” CD-ROM or WORM devices will be “attached” to the cd driver.
The system utility disklabel(8) may be used to read the synthesized disk label structure, which will contain correct figures for the size of the CD-ROM should that information be required.
IOCTLS #
The following ioctl(2) calls which apply to CD-ROM drives are defined in the header files <sys/cdio.h> and <sys/dkio.h>.
DIOCGDINFO
, DIOCSDINFO
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 disklabel(5).
CDIOCPLAYTRACKS
struct ioc_play_track *
Start audio playback given a track address and length. The structure is defined as follows:
struct ioc_play_track { u_char start_track; u_char start_index; u_char end_track; u_char end_index; };
CDIOCPLAYBLOCKS
struct ioc_play_blocks *
Start audio playback given a block address and length. The structure is defined as follows:
struct ioc_play_blocks { int blk; int len; };
CDIOCPLAYMSF
struct ioc_play_msf *
Start audio playback given a “minutes-seconds-frames” address and length. The structure is defined as follows:
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; };
CDIOCREADSUBCHANNEL
struct ioc_read_subchannel *
Read information from the subchannel at the location specified by this structure:
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; };
CDIOREADTOCHEADER
struct ioc_toc_header *
Return summary information about the table of contents for the mounted CD-ROM. The information is returned into the following structure:
struct ioc_toc_header { u_short len; u_char starting_track; u_char ending_track; };
CDIOREADTOCENTRIES
struct ioc_read_toc_entry *
Return information from the table of contents entries mentioned. The argument structure is defined as follows:
struct ioc_read_toc_entry { u_char address_format; u_char starting_track; u_short data_len; struct cd_toc_entry *data; };
The requested data is written into an area of size
data_len
and pointed to bydata
.
CDIOCSETPATCH
struct ioc_patch *
Attach various audio channels to various output channels. The argument structure is defined thusly:
struct ioc_patch { u_char patch[4]; /* one for each channel */ };
CDIOCGETVOL
, CDIOCSETVOL
struct ioc_vol *
Get (set) information about the volume settings of the output channels. The argument structure is as follows:
struct ioc_vol { u_char vol[4]; /* one for each channel */ };
CDIOCSETMONO
Patch all output channels to all source channels.
CDIOCSETSTEREO
Patch left source channel to the left output channel and the right source channel to the right output channel.
CDIOCSETMUTE
Mute output without changing the volume settings.
CDIOCSETLEFT
, CDIOCSETRIGHT
Attach both output channels to the left (right) source channel.
CDIOCSETDEBUG
, CDIOCCLRDEBUG
Turn on (off) debugging for the appropriate device.
CDIOCPAUSE
, CDIOCRESUME
Pause (resume) audio play, without resetting the location of the read-head.
CDIOCRESET
Reset the drive.
CDIOCSTART
, CDIOCSTOP
Tell the drive to spin-up (-down) the CD-ROM.
CDIOCALLOW
, CDIOCPREVENT
Tell the drive to allow (prevent) manual ejection of the CD-ROM disc. Not all drives support this feature.
CDIOCEJECT
Eject the CD-ROM.
In addition the general scsi(4) ioctls may be used with the cd driver, if used against the `whole disk’ partition (i.e., /dev/rcd0c).
NOTES #
When a CD-ROM is changed in a drive controlled by the cd 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.
The audio code in the cd driver only supports SCSI-2 standard audio commands. Because many CD-ROM manufacturers have not followed the standard, there are many CD-ROM drives for which audio will not work. Some work is planned to support some of the more common “broken” CD-ROM drives; however, this is not yet under way.
FILES #
/dev/cd[0-9][a-p]
block mode CD-ROM devices
/dev/rcd[0-9][a-p]
raw mode CD-ROM devices
DIAGNOSTICS #
None.
SEE ALSO #
cdio(1), eject(1), ioctl(2), intro(4), scsi(4), scsibus(4), sd(4), wd(4), disklabel(5), disklabel(8)
HISTORY #
The cd driver appeared in 386BSD 0.1.
BUGS #
The names of the structures used for the third argument to ioctl() were poorly chosen, and a number of spelling errors have survived in the names of the ioctl() commands.
OpenBSD 7.5 - August 27, 2015