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Based on kernel version 3.3. Page generated on 2012-03-23 21:25 EST.

	\documentclass{article}
	\def\version{$Id: cdrom-standard.tex,v 1.9 1997/12/28 15:42:49 david Exp $}
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	\def\linux{{\sc Linux}}
	\def\cdrom{{\sc cd-rom}}
	\def\UCD{{\sc Uniform cd-rom Driver}}
	\def\cdromc{{\tt {cdrom.c}}}
	\def\cdromh{{\tt {cdrom.h}}}
	\def\fo{\sl}                    % foreign words
	\def\ie{{\fo i.e.}}
	\def\eg{{\fo e.g.}}
	
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	\begin{document}
	\title{A \linux\ \cdrom\ standard}
	\author{David van Leeuwen\\{\normalsize\tt david@ElseWare.cistron.nl}
	\\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}}
	\\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}}
	\date{12 March 1999}
	
	\maketitle
	
	\newsection{Introduction}
	
	\linux\ is probably the Unix-like operating system that supports
	the widest variety of hardware devices. The reasons for this are
	presumably 
	\begin{itemize} 
	\item 
	  The large list of hardware devices available for the many platforms
	  that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.)
	\item 
	  The open design of the operating system, such that anybody can write a
	  driver for \linux.
	\item 
	  There is plenty of source code around as examples of how to write a driver.
	\end{itemize}
	The openness of \linux, and the many different types of available
	hardware has allowed \linux\ to support many different hardware devices.
	Unfortunately, the very openness that has allowed \linux\ to support
	all these different devices has also allowed the behavior of each
	device driver to differ significantly from one device to another.
	This divergence of behavior has been very significant for \cdrom\
	devices; the way a particular drive reacts to a `standard' $ioctl()$
	call varies greatly from one device driver to another. To avoid making
	their drivers totally inconsistent, the writers of \linux\ \cdrom\
	drivers generally created new device drivers by understanding, copying,
	and then changing an existing one. Unfortunately, this practice did not
	maintain uniform behavior across all the \linux\ \cdrom\ drivers. 
	
	This document describes an effort to establish Uniform behavior across
	all the different \cdrom\ device drivers for \linux. This document also
	defines the various $ioctl$s, and how the low-level \cdrom\ device
	drivers should implement them. Currently (as of the \linux\ 2.1.$x$
	development kernels) several low-level \cdrom\ device drivers, including
	both IDE/ATAPI and SCSI, now use this Uniform interface.
	
	When the \cdrom\ was developed, the interface between the \cdrom\ drive
	and the computer was not specified in the standards. As a result, many
	different \cdrom\ interfaces were developed. Some of them had their
	own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
	manufacturers adopted an existing electrical interface and changed
	the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
	adapted their drives to one or more of the already existing electrical
	interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
	most of the `NoName' manufacturers). In cases where a new drive really
	brought its own interface or used its own command set and flow control
	scheme, either a separate driver had to be written, or an existing
	driver had to be enhanced. History has delivered us \cdrom\ support for
	many of these different interfaces. Nowadays, almost all new \cdrom\
	drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
	manufacturer will create a new interface. Even finding drives for the
	old proprietary interfaces is getting difficult.
	
	When (in the 1.3.70's) I looked at the existing software interface,
	which was expressed through \cdromh, it appeared to be a rather wild
	set of commands and data formats.\footnote{I cannot recollect what
	kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
	latest kernel that I was indirectly involved in.} It seemed that many
	features of the software interface had been added to accommodate the
	capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
	importantly, it appeared that the behavior of the `standard' commands
	was different for most of the different drivers: \eg, some drivers
	close the tray if an $open()$ call occurs when the tray is open, while
	others do not. Some drivers lock the door upon opening the device, to
	prevent an incoherent file system, but others don't, to allow software
	ejection. Undoubtedly, the capabilities of the different drives vary,
	but even when two drives have the same capability their drivers'
	behavior was usually different.
	
	I decided to start a discussion on how to make all the \linux\ \cdrom\
	drivers behave more uniformly. I began by contacting the developers of
	the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
	encouraged me to write the \UCD\ which this document is intended to
	describe. The implementation of the \UCD\ is in the file \cdromc. This
	driver is intended to be an additional software layer that sits on top
	of the low-level device drivers for each \cdrom\ drive. By adding this
	additional layer, it is possible to have all the different \cdrom\
	devices behave {\em exactly\/} the same (insofar as the underlying
	hardware will allow).
	
	The goal of the \UCD\ is {\em not\/} to alienate driver developers who
	have not yet taken steps to support this effort. The goal of \UCD\ is
	simply to give people writing application programs for \cdrom\ drives
	{\em one\/} \linux\ \cdrom\ interface with consistent behavior for all
	\cdrom\ devices. In addition, this also provides a consistent interface
	between the low-level device driver code and the \linux\ kernel. Care
	is taken that 100\,\% compatibility exists with the data structures and
	programmer's interface defined in \cdromh. This guide was written to
	help \cdrom\ driver developers adapt their code to use the \UCD\ code
	defined in \cdromc.
	
	Personally, I think that the most important hardware interfaces are
	the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
	of hardware drop continuously, it is also likely that people may have
	more than one \cdrom\ drive, possibly of mixed types. It is important
	that these drives behave in the same way. In December 1994, one of the
	cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
	drive. In the months that I was busy writing a \linux\ driver for it,
	proprietary drives became obsolete and IDE/ATAPI drives became the
	standard. At the time of the last update to this document (November
	1997) it is becoming difficult to even {\em find} anything less than a
	16 speed \cdrom\ drive, and 24 speed drives are common.
	
	\newsection{Standardizing through another software level}
	\label{cdrom.c}
	
	At the time this document was conceived, all drivers directly
	implemented the \cdrom\ $ioctl()$ calls through their own routines. This
	led to the danger of different drivers forgetting to do important things
	like checking that the user was giving the driver valid data. More
	importantly, this led to the divergence of behavior, which has already
	been discussed.
	
	For this reason, the \UCD\ was created to enforce consistent \cdrom\
	drive behavior, and to provide a common set of services to the various
	low-level \cdrom\ device drivers. The \UCD\ now provides another
	software-level, that separates the $ioctl()$ and $open()$ implementation
	from the actual hardware implementation. Note that this effort has
	made few changes which will affect a user's application programs. The
	greatest change involved moving the contents of the various low-level
	\cdrom\ drivers' header files to the kernel's cdrom directory. This was
	done to help ensure that the user is only presented with only one cdrom
	interface, the interface defined in \cdromh.
	
	\cdrom\ drives are specific enough (\ie, different from other
	block-devices such as floppy or hard disc drives), to define a set
	of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
	These operations are different from the classical block-device file
	operations, $<block-device>_fops$.
	
	The routines for the \UCD\ interface level are implemented in the file
	\cdromc. In this file, the \UCD\ interfaces with the kernel as a block
	device by registering the following general $struct\ file_operations$:
	$$
	\halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	struct& file_operations\ cdrom_fops = \{\hidewidth\cr
	        &NULL,                  & lseek \cr
	        &block_read,            & read---general block-dev read \cr
	        &block_write,           & write---general block-dev write \cr
	        &NULL,                  & readdir \cr
	        &NULL,                  & select \cr
	        &cdrom_ioctl,           & ioctl \cr
	        &NULL,                  & mmap \cr
	        &cdrom_open,            & open \cr
	        &cdrom_release,         & release \cr
	        &NULL,                  & fsync \cr
	        &NULL,                  & fasync \cr
	        &cdrom_media_changed,   & media change \cr
	        &NULL                   & revalidate \cr
	\};\cr
	}
	$$ 
	
	Every active \cdrom\ device shares this $struct$. The routines
	declared above are all implemented in \cdromc, since this file is the
	place where the behavior of all \cdrom-devices is defined and
	standardized. The actual interface to the various types of \cdrom\ 
	hardware is still performed by various low-level \cdrom-device
	drivers. These routines simply implement certain {\em capabilities\/}
	that are common to all \cdrom\ (and really, all removable-media
	devices).
	
	Registration of a low-level \cdrom\ device driver is now done through
	the general routines in \cdromc, not through the Virtual File System
	(VFS) any more. The interface implemented in \cdromc\ is carried out
	through two general structures that contain information about the
	capabilities of the driver, and the specific drives on which the
	driver operates. The structures are:
	\begin{description}
	\item[$cdrom_device_ops$] 
	  This structure contains information about the low-level driver for a
	  \cdrom\ device. This structure is conceptually connected to the major
	  number of the device (although some drivers may have different
	  major numbers, as is the case for the IDE driver).
	\item[$cdrom_device_info$] 
	  This structure contains information about a particular \cdrom\ drive,
	  such as its device name, speed, etc. This structure is conceptually
	  connected to the minor number of the device.
	\end{description}
	
	Registering a particular \cdrom\ drive with the \UCD\ is done by the
	low-level device driver though a call to:
	$$register_cdrom(struct\ cdrom_device_info * <device>_info)  
	$$
	The device information structure, $<device>_info$, contains all the
	information needed for the kernel to interface with the low-level
	\cdrom\ device driver. One of the most important entries in this
	structure is a pointer to the $cdrom_device_ops$ structure of the
	low-level driver.
	
	The device operations structure, $cdrom_device_ops$, contains a list
	of pointers to the functions which are implemented in the low-level
	device driver. When \cdromc\ accesses a \cdrom\ device, it does it
	through the functions in this structure. It is impossible to know all
	the capabilities of future \cdrom\ drives, so it is expected that this
	list may need to be expanded from time to time as new technologies are
	developed. For example, CD-R and CD-R/W drives are beginning to become
	popular, and support will soon need to be added for them. For now, the
	current $struct$ is:
	$$
	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
	  $/*$ \rm# $*/$\hfil\cr
	struct& cdrom_device_ops\ \{ \hidewidth\cr
	  &int& (* open)(struct\ cdrom_device_info *, int)\cr
	  &void& (* release)(struct\ cdrom_device_info *);\cr 
	  &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr     
	  &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 
	  &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
	  &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
	  &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
	  &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
	  &int& (* get_last_session) (struct\ cdrom_device_info *, 
	        struct\ cdrom_multisession *{});\cr
	  &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
	  &int& (* reset)(struct\ cdrom_device_info *);\cr
	  &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
	        void *{});\cr 
	  &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
	        unsigned\ long);\cr
	\noalign{\medskip}
	  &const\ int& capability;& capability flags \cr
	  &int& n_minors;& number of active minor devices \cr
	\};\cr
	}
	$$
	When a low-level device driver implements one of these capabilities,
	it should add a function pointer to this $struct$. When a particular
	function is not implemented, however, this $struct$ should contain a
	NULL instead. The $capability$ flags specify the capabilities of the
	\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
	is registered with the \UCD. The value $n_minors$ should be a positive
	value indicating the number of minor devices that are supported by
	the low-level device driver, normally~1. Although these two variables
	are `informative' rather than `operational,' they are included in
	$cdrom_device_ops$ because they describe the capability of the {\em
	driver\/} rather than the {\em drive}. Nomenclature has always been
	difficult in computer programming.
	
	Note that most functions have fewer parameters than their
	$blkdev_fops$ counterparts. This is because very little of the
	information in the structures $inode$ and $file$ is used. For most
	drivers, the main parameter is the $struct$ $cdrom_device_info$, from
	which the major and minor number can be extracted. (Most low-level
	\cdrom\ drivers don't even look at the major and minor number though,
	since many of them only support one device.) This will be available
	through $dev$ in $cdrom_device_info$ described below.
	
	The drive-specific, minor-like information that is registered with
	\cdromc, currently contains the following fields:
	$$
	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
	  $/*$ \rm# $*/$\hfil\cr
	struct& cdrom_device_info\ \{ \hidewidth\cr
	  & struct\ cdrom_device_ops *& ops;& device operations for this major\cr
	  & struct\ cdrom_device_info *& next;& next device_info for this major\cr
	  & void *&  handle;& driver-dependent data\cr
	\noalign{\medskip}
	  & kdev_t&  dev;& device number (incorporates minor)\cr
	  & int& mask;& mask of capability: disables them \cr
	  & int& speed;& maximum speed for reading data \cr
	  & int& capacity;& number of discs in a jukebox \cr
	\noalign{\medskip}
	  &int& options : 30;& options flags \cr
	  &unsigned& mc_flags : 2;& media-change buffer flags \cr
	  & int& use_count;& number of times device is opened\cr
	  & char& name[20];& name of the device type\cr
	\}\cr
	}$$
	Using this $struct$, a linked list of the registered minor devices is
	built, using the $next$ field. The device number, the device operations
	struct and specifications of properties of the drive are stored in this
	structure.
	
	The $mask$ flags can be used to mask out some of the capabilities listed
	in $ops\to capability$, if a specific drive doesn't support a feature
	of the driver. The value $speed$ specifies the maximum head-rate of the
	drive, measured in units of normal audio speed (176\,kB/sec raw data or
	150\,kB/sec file system data). The value $n_discs$ should reflect the
	number of discs the drive can hold simultaneously, if it is designed
	as a juke-box, or otherwise~1. The parameters are declared $const$
	because they describe properties of the drive, which don't change after
	registration.
	
	A few registers contain variables local to the \cdrom\ drive. The
	flags $options$ are used to specify how the general \cdrom\ routines
	should behave. These various flags registers should provide enough
	flexibility to adapt to the different users' wishes (and {\em not\/} the
	`arbitrary' wishes of the author of the low-level device driver, as is
	the case in the old scheme). The register $mc_flags$ is used to buffer
	the information from $media_changed()$ to two separate queues. Other
	data that is specific to a minor drive, can be accessed through $handle$,
	which can point to a data structure specific to the low-level driver.
	The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
	initialized.
	
	The intermediate software layer that \cdromc\ forms will perform some
	additional bookkeeping. The use count of the device (the number of
	processes that have the device opened) is registered in $use_count$. The
	function $cdrom_ioctl()$ will verify the appropriate user-memory regions
	for read and write, and in case a location on the CD is transferred,
	it will `sanitize' the format by making requests to the low-level
	drivers in a standard format, and translating all formats between the
	user-software and low level drivers. This relieves much of the drivers'
	memory checking and format checking and translation. Also, the necessary
	structures will be declared on the program stack.
	
	The implementation of the functions should be as defined in the
	following sections. Two functions {\em must\/} be implemented, namely
	$open()$ and $release()$. Other functions may be omitted, their
	corresponding capability flags will be cleared upon registration.
	Generally, a function returns zero on success and negative on error. A
	function call should return only after the command has completed, but of
	course waiting for the device should not use processor time.
	
	\subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
	
	$Open()$ should try to open the device for a specific $purpose$, which
	can be either:
	\begin{itemize}
	\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
	user commands {\tt {dd}} or {\tt {cat}}.  
	\item[1] Open for $ioctl$ commands, as done by audio-CD playing
	programs.
	\end{itemize}
	Notice that any strategic code (closing tray upon $open()$, etc.)\ is
	done by the calling routine in \cdromc, so the low-level routine
	should only be concerned with proper initialization, such as spinning
	up the disc, etc. % and device-use count
	
	
	\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
	
	
	Device-specific actions should be taken such as spinning down the device.
	However, strategic actions such as ejection of the tray, or unlocking
	the door, should be left over to the general routine $cdrom_release()$.
	This is the only function returning type $void$.
	
	\subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
	\label{drive status}
	
	The function $drive_status$, if implemented, should provide
	information on the status of the drive (not the status of the disc,
	which may or may not be in the drive). If the drive is not a changer,
	$slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 
	$$
	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	CDS_NO_INFO& no information available\cr
	CDS_NO_DISC& no disc is inserted, tray is closed\cr
	CDS_TRAY_OPEN& tray is opened\cr
	CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
	CDS_DISC_OK& a disc is loaded and everything is fine\cr
	}
	$$
	
	\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
	
	This function is very similar to the original function in $struct\ 
	file_operations$. It returns 1 if the medium of the device $cdi\to
	dev$ has changed since the last call, and 0 otherwise. The parameter
	$disc_nr$ identifies a specific slot in a juke-box, it should be
	ignored for single-disc drives.  Note that by `re-routing' this
	function through $cdrom_media_changed()$, we can implement separate
	queues for the VFS and a new $ioctl()$ function that can report device
	changes to software (\eg, an auto-mounting daemon).
	
	\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
	
	This function, if implemented, should control the tray movement. (No
	other function should control this.) The parameter $position$ controls
	the desired direction of movement:
	\begin{itemize}
	\item[0] Close tray
	\item[1] Open tray
	\end{itemize}
	This function returns 0 upon success, and a non-zero value upon
	error. Note that if the tray is already in the desired position, no
	action need be taken, and the return value should be 0. 
	
	\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
	
	This function (and no other code) controls locking of the door, if the
	drive allows this. The value of $lock$ controls the desired locking
	state:
	\begin{itemize}
	\item[0] Unlock door, manual opening is allowed
	\item[1] Lock door, tray cannot be ejected manually
	\end{itemize}
	This function returns 0 upon success, and a non-zero value upon
	error. Note that if the door is already in the requested state, no
	action need be taken, and the return value should be 0. 
	
	\subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
	
	Some \cdrom\ drives are capable of changing their head-speed. There
	are several reasons for changing the speed of a \cdrom\ drive. Badly
	pressed \cdrom s may benefit from less-than-maximum head rate. Modern
	\cdrom\ drives can obtain very high head rates (up to $24\times$ is
	common).  It has been reported that these drives can make reading
	errors at these high speeds, reducing the speed can prevent data loss
	in these circumstances.  Finally, some of these drives can
	make an annoyingly loud noise, which a lower speed may reduce. %Finally,
	%although the audio-low-pass filters probably aren't designed for it,
	%more than real-time playback of audio might be used for high-speed
	%copying of audio tracks.
	
	This function specifies the speed at which data is read or audio is
	played back. The value of $speed$ specifies the head-speed of the
	drive, measured in units of standard cdrom speed (176\,kB/sec raw data
	or 150\,kB/sec file system data). So to request that a \cdrom\ drive
	operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
	with $speed=2$. The special value `0' means `auto-selection', \ie,
	maximum data-rate or real-time audio rate. If the drive doesn't have
	this `auto-selection' capability, the decision should be made on the
	current disc loaded and the return value should be positive. A negative
	return value indicates an error.
	
	\subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
	
	If the drive can store multiple discs (a juke-box) this function
	will perform disc selection. It should return the number of the
	selected disc on success, a negative value on error. Currently, only
	the ide-cd driver supports this functionality.
	
	\subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\
	  cdrom_multisession * ms_info)$}
	
	This function should implement the old corresponding $ioctl()$. For
	device $cdi\to dev$, the start of the last session of the current disc
	should be returned in the pointer argument $ms_info$. Note that
	routines in \cdromc\ have sanitized this argument: its requested
	format will {\em always\/} be of the type $CDROM_LBA$ (linear block
	addressing mode), whatever the calling software requested. But
	sanitization goes even further: the low-level implementation may
	return the requested information in $CDROM_MSF$ format if it wishes so
	(setting the $ms_info\rightarrow addr_format$ field appropriately, of
	course) and the routines in \cdromc\ will make the transformation if
	necessary. The return value is 0 upon success.
	
	\subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
	  cdrom_mcn * mcn)$}
	
	Some discs carry a `Media Catalog Number' (MCN), also called
	`Universal Product Code' (UPC). This number should reflect the number
	that is generally found in the bar-code on the product. Unfortunately,
	the few discs that carry such a number on the disc don't even use the
	same format. The return argument to this function is a pointer to a
	pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
	expected as a 13-character string, terminated by a null-character.
	
	\subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
	
	This call should perform a hard-reset on the drive (although in
	circumstances that a hard-reset is necessary, a drive may very well not
	listen to commands anymore). Preferably, control is returned to the
	caller only after the drive has finished resetting. If the drive is no
	longer listening, it may be wise for the underlying low-level cdrom
	driver to time out.
	
	\subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
	  int\ cmd, void * arg)$}
	
	Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
	implemented by the routines described above, and hence the function
	$cdrom_ioctl$ will use those. However, most $ioctl$s deal with
	audio-control. We have decided to leave these to be accessed through a
	single function, repeating the arguments $cmd$ and $arg$. Note that
	the latter is of type $void*{}$, rather than $unsigned\ long\
	int$. The routine $cdrom_ioctl()$ does do some useful things,
	though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
	Seconds, Frames) for all audio calls. It also verifies the memory
	location of $arg$, and reserves stack-memory for the argument. This
	makes implementation of the $audio_ioctl()$ much simpler than in the
	old driver scheme. For example, you may look up the function
	$cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
	this documentation. 
	
	An unimplemented ioctl should return $-ENOSYS$, but a harmless request
	(\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
	errors should be according to the standards, whatever they are. When
	an error is returned by the low-level driver, the \UCD\ tries whenever
	possible to return the error code to the calling program. (We may decide
	to sanitize the return value in $cdrom_ioctl()$ though, in order to
	guarantee a uniform interface to the audio-player software.)
	
	\subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\
	  cmd, unsigned\ long\ arg)$}
	
	Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
	they are introduced to service some capabilities of certain drives. In
	fact, there are 6 different $ioctl$s for reading data, either in some
	particular kind of format, or audio data. Not many drives support
	reading audio tracks as data, I believe this is because of protection
	of copyrights of artists. Moreover, I think that if audio-tracks are
	supported, it should be done through the VFS and not via $ioctl$s. A
	problem here could be the fact that audio-frames are 2352 bytes long,
	so either the audio-file-system should ask for 75264 bytes at once
	(the least common multiple of 512 and 2352), or the drivers should
	bend their backs to cope with this incoherence (to which I would be
	opposed).  Furthermore, it is very difficult for the hardware to find
	the exact frame boundaries, since there are no synchronization headers
	in audio frames.  Once these issues are resolved, this code should be
	standardized in \cdromc.
	
	Because there are so many $ioctl$s that seem to be introduced to
	satisfy certain drivers,\footnote{Is there software around that
	  actually uses these? I'd be interested!} any `non-standard' $ioctl$s
	are routed through the call $dev_ioctl()$. In principle, `private'
	$ioctl$s should be numbered after the device's major number, and not
	the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
	non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2,
	  CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK,
	  CDROMPLAY\-BLK and CDROM\-READALL}.
	
	
	\subsection{\cdrom\ capabilities}
	\label{capability}
	
	Instead of just implementing some $ioctl$ calls, the interface in
	\cdromc\ supplies the possibility to indicate the {\em capabilities\/}
	of a \cdrom\ drive. This can be done by ORing any number of
	capability-constants that are defined in \cdromh\ at the registration
	phase. Currently, the capabilities are any of:
	$$
	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	CDC_CLOSE_TRAY& can close tray by software control\cr
	CDC_OPEN_TRAY& can open tray\cr
	CDC_LOCK& can lock and unlock the door\cr
	CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
	CDC_SELECT_DISC& drive is juke-box\cr
	CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
	CDC_MCN& can read Media Catalog Number\cr
	CDC_MEDIA_CHANGED& can report if disc has changed\cr
	CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
	CDC_RESET& hard reset device\cr
	CDC_IOCTLS& driver has non-standard ioctls\cr
	CDC_DRIVE_STATUS& driver implements drive status\cr
	}
	$$
	The capability flag is declared $const$, to prevent drivers from
	accidentally tampering with the contents. The capability fags actually
	inform \cdromc\ of what the driver can do. If the drive found
	by the driver does not have the capability, is can be masked out by
	the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
	driver has implemented the code for loading and ejecting \cdrom's, and
	hence its corresponding flags in $capability$ will be set. But a SCSI
	\cdrom\ drive might be a caddy system, which can't load the tray, and
	hence for this drive the $cdrom_device_info$ struct will have set
	the $CDC_CLOSE_TRAY$ bit in $mask$.
	
	In the file \cdromc\ you will encounter many constructions of the type
	$$\it
	if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 
	   \mathrel{\&} CDC_<capability>) \ldots
	$$
	There is no $ioctl$ to set the mask\dots The reason is that
	I think it is better to control the {\em behavior\/} rather than the
	{\em capabilities}.
	
	\subsection{Options}
	
	A final flag register controls the {\em behavior\/} of the \cdrom\
	drives, in order to satisfy different users' wishes, hopefully
	independently of the ideas of the respective author who happened to
	have made the drive's support available to the \linux\ community. The
	current behavior options are:
	$$
	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
	CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
	CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
	 purpose for $open()$\cr
	CDO_LOCK& try to lock door if device is opened\cr
	CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
	}
	$$
	
	The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
	CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
	interface and software standards. Before you protest, there are two
	new $ioctl$s implemented in \cdromc, that allow you to control the
	behavior by software. These are:
	$$
	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
	CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
	}
	$$
	One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
	newsection we explain what the need for this option is.
	
	A software package {\tt setcd}, available from the Debian distribution
	and {\tt sunsite.unc.edu}, allows user level control of these flags. 
	
	\newsection{The need to know the purpose of opening the \cdrom\ device}
	
	Traditionally, Unix devices can be used in two different `modes',
	either by reading/writing to the device file, or by issuing
	controlling commands to the device, by the device's $ioctl()$
	call. The problem with \cdrom\ drives, is that they can be used for
	two entirely different purposes. One is to mount removable
	file systems, \cdrom s, the other is to play audio CD's. Audio commands
	are implemented entirely through $ioctl$s, presumably because the
	first implementation (SUN?) has been such. In principle there is
	nothing wrong with this, but a good control of the `CD player' demands
	that the device can {\em always\/} be opened in order to give the
	$ioctl$ commands, regardless of the state the drive is in. 
	
	On the other hand, when used as a removable-media disc drive (what the
	original purpose of \cdrom s is) we would like to make sure that the
	disc drive is ready for operation upon opening the device. In the old
	scheme, some \cdrom\ drivers don't do any integrity checking, resulting
	in a number of i/o errors reported by the VFS to the kernel when an
	attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
	particularly elegant way to find out that there is no \cdrom\ inserted;
	it more-or-less looks like the old IBM-PC trying to read an empty floppy
	drive for a couple of seconds, after which the system complains it
	can't read from it. Nowadays we can {\em sense\/} the existence of a
	removable medium in a drive, and we believe we should exploit that
	fact. An integrity check on opening of the device, that verifies the
	availability of a \cdrom\ and its correct type (data), would be
	desirable.
	
	These two ways of using a \cdrom\ drive, principally for data and
	secondarily for playing audio discs, have different demands for the
	behavior of the $open()$ call. Audio use simply wants to open the
	device in order to get a file handle which is needed for issuing
	$ioctl$ commands, while data use wants to open for correct and
	reliable data transfer. The only way user programs can indicate what
	their {\em purpose\/} of opening the device is, is through the $flags$
	parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
	implemented (some drivers implement checking for write-related flags,
	but this is not strictly necessary if the device file has correct
	permission flags). Most option flags simply don't make sense to
	\cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and
	$O_SYNC$ have no meaning to a \cdrom. 
	
	We therefore propose to use the flag $O_NONBLOCK$ to indicate
	that the device is opened just for issuing $ioctl$
	commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
	subsequent calls to the device don't cause the calling process to
	wait. We could interpret this as ``don't wait until someone has
	inserted some valid data-\cdrom.'' Thus, our proposal of the
	implementation for the $open()$ call for \cdrom s is:
	\begin{itemize}
	\item If no other flags are set than $O_RDONLY$, the device is opened
	for data transfer, and the return value will be 0 only upon successful
	initialization of the transfer. The call may even induce some actions
	on the \cdrom, such as closing the tray.  
	\item If the option flag $O_NONBLOCK$ is set, opening will always be
	successful, unless the whole device doesn't exist. The drive will take
	no actions whatsoever. 
	\end{itemize}
	
	\subsection{And what about standards?}
	
	You might hesitate to accept this proposal as it comes from the
	\linux\ community, and not from some standardizing institute. What
	about SUN, SGI, HP and all those other Unix and hardware vendors?
	Well, these companies are in the lucky position that they generally
	control both the hardware and software of their supported products,
	and are large enough to set their own standard. They do not have to
	deal with a dozen or more different, competing hardware
	configurations.\footnote{Incidentally, I think that SUN's approach to
	mounting \cdrom s is very good in origin: under Solaris a
	volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
	{/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
	further and have {\em every\/} \cdrom\ on the local area network be
	mounted at the similar location, \ie, no matter in which particular
	machine you insert a \cdrom, it will always appear at the same
	position in the directory tree, on every system. When I wanted to
	implement such a user-program for \linux, I came across the
	differences in behavior of the various drivers, and the need for an
	$ioctl$ informing about media changes.}
	
	We believe that using $O_NONBLOCK$ to indicate that a device is being opened
	for $ioctl$ commands only can be easily introduced in the \linux\
	community. All the CD-player authors will have to be informed, we can
	even send in our own patches to the programs. The use of $O_NONBLOCK$
	has most likely no influence on the behavior of the CD-players on
	other operating systems than \linux. Finally, a user can always revert
	to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
	CDO_USE_FFLAGS)$. 
	
	\subsection{The preferred strategy of $open()$}
	
	The routines in \cdromc\ are designed in such a way that run-time
	configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
	can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
	modes of operation can be set:
	\begin{description}
	\item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
	is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
	future.) If the device is not yet opened by any other process, and if
	the device is being opened for data ($O_NONBLOCK$ is not set) and the
	tray is found to be open, an attempt to close the tray is made. Then,
	it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
	set, that it contains tracks of type `data mode 1.' Only if all tests
	are passed is the return value zero. The door is locked to prevent file
	system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
	set), no actions are taken and a value of 0 will be returned. 
	\item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This
	mimics the behavior of the current sbpcd-driver. The option flags are
	ignored, the tray is closed on the first open, if necessary. Similarly,
	the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
	it is automatically ejected, such that the user can replace it.
	\end{description} 
	We hope that these option can convince everybody (both driver
	maintainers and user program developers) to adopt the new \cdrom\
	driver scheme and option flag interpretation.
	
	\newsection{Description of routines in \cdromc}
	
	Only a few routines in \cdromc\ are exported to the drivers. In this
	new section we will discuss these, as well as the functions that `take
	over' the \cdrom\ interface to the kernel. The header file belonging
	to \cdromc\ is called \cdromh. Formerly, some of the contents of this
	file were placed in the file {\tt {ucdrom.h}}, but this file has now been
	merged back into \cdromh.
	
	\subsection{$Struct\ file_operations\ cdrom_fops$}
	
	The contents of this structure were described in section~\ref{cdrom.c}.
	A pointer to this structure is assigned to the $fops$ field
	of the $struct gendisk$.
	
	\subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
	
	This function is used in about the same way one registers $cdrom_fops$
	with the kernel, the device operations and information structures,
	as described in section~\ref{cdrom.c}, should be registered with the
	\UCD:
	$$
	register_cdrom(\&<device>_info));
	$$
	This function returns zero upon success, and non-zero upon
	failure. The structure $<device>_info$ should have a pointer to the
	driver's $<device>_dops$, as in 
	$$
	\vbox{\halign{&$#$\hfil\cr
	struct\ &cdrom_device_info\ <device>_info = \{\cr
	& <device>_dops;\cr
	&\ldots\cr
	\}\cr
	}}$$
	Note that a driver must have one static structure, $<device>_dops$, while
	it may have as many structures $<device>_info$ as there are minor devices
	active. $Register_cdrom()$ builds a linked list from these. 
	
	\subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
	
	Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
	the minor device from the list. If it was the last registered minor for
	the low-level driver, this disconnects the registered device-operation
	routines from the \cdrom\ interface. This function returns zero upon
	success, and non-zero upon failure.
	
	\subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
	
	This function is not called directly by the low-level drivers, it is
	listed in the standard $cdrom_fops$. If the VFS opens a file, this
	function becomes active. A strategy is implemented in this routine,
	taking care of all capabilities and options that are set in the
	$cdrom_device_ops$ connected to the device. Then, the program flow is
	transferred to the device_dependent $open()$ call.
	
	\subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
	*fp)$}
	
	This function implements the reverse-logic of $cdrom_open()$, and then
	calls the device-dependent $release()$ routine. When the use-count has
	reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
	and $invalidate_buffers(dev)$.
	
	
	\subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
	unsigned\ int\ cmd, unsigned\ long\ arg)$}
	\label{cdrom-ioctl}
	
	This function handles all the standard $ioctl$ requests for \cdrom\
	devices in a uniform way. The different calls fall into three
	categories: $ioctl$s that can be directly implemented by device
	operations, ones that are routed through the call $audio_ioctl()$, and
	the remaining ones, that are presumable device-dependent. Generally, a
	negative return value indicates an error.
	
	\subsubsection{Directly implemented $ioctl$s}
	\label{ioctl-direct}
	
	The following `old' \cdrom-$ioctl$s are implemented by directly
	calling device-operations in $cdrom_device_ops$, if implemented and
	not masked:
	\begin{description}
	\item[CDROMMULTISESSION] Requests the last session on a \cdrom.
	\item[CDROMEJECT] Open tray. 
	\item[CDROMCLOSETRAY] Close tray.
	\item[CDROMEJECT_SW] If $arg\not=0$, set behavior to auto-close (close
	tray on first open) and auto-eject (eject on last release), otherwise
	set behavior to non-moving on $open()$ and $release()$ calls.
	\item[CDROM_GET_MCN] Get the Media Catalog Number from a CD.
	\end{description}
	
	\subsubsection{$Ioctl$s routed through $audio_ioctl()$}
	\label{ioctl-audio}
	
	The following set of $ioctl$s are all implemented through a call to
	the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
	allocation are performed in $cdrom_ioctl()$, and also sanitization of
	address format ($CDROM_LBA$/$CDROM_MSF$) is done.
	\begin{description}
	\item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
	cdrom_subchnl *{}$.
	\item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type
	$struct\ cdrom_tochdr *{}$. 
	\item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and
	specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
	\item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
	Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
	\item[CDROMPLAYTRKIND] Play audio fragment in track-index format
	delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
	\item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
	cdrom_volctrl *{}$.
	\item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
	cdrom_volctrl *{}$.
	\item[CDROMSTART] Spin up disc.
	\item[CDROMSTOP] Stop playback of audio fragment.
	\item[CDROMPAUSE] Pause playback of audio fragment.
	\item[CDROMRESUME] Resume playing.
	\end{description}
	
	\subsubsection{New $ioctl$s in \cdromc}
	
	The following $ioctl$s have been introduced to allow user programs to
	control the behavior of individual \cdrom\ devices. New $ioctl$
	commands can be identified by the underscores in their names.
	\begin{description}
	\item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
	option flag register after modification. Use  $arg = \rm0$ for reading
	the current flags.
	\item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns
	  the option flag register after modification.
	\item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as
	  by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or
	  150\,kB/sec file system data). The value 0 means `auto-select', \ie,
	  play audio discs at real time and data discs at maximum speed. The value
	  $arg$ is checked against the maximum head rate of the drive found in the
	  $cdrom_dops$.
	\item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box.
	  First disc is numbered 0. The number $arg$ is checked against the
	  maximum number of discs in the juke-box found in the $cdrom_dops$.
	\item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since
	  the last call. Note that calls to $cdrom_media_changed$ by the VFS
	  are treated by an independent queue, so both mechanisms will detect
	  a media change once. For juke-boxes, an extra argument $arg$
	  specifies the slot for which the information is given. The special
	  value $CDSL_CURRENT$ requests that information about the currently
	  selected slot be returned.
	\item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to
	  $drive_status()$. Return values are defined in section~\ref{drive
	   status}. Note that this call doesn't return information on the
	  current playing activity of the drive; this can be polled through an
	  $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument
	  $arg$ specifies the slot for which (possibly limited) information is
	  given. The special value $CDSL_CURRENT$ requests that information
	  about the currently selected slot be returned.
	\item[CDROM_DISC_STATUS] Returns the type of the disc currently in the
	  drive.  It should be viewed as a complement to $CDROM_DRIVE_STATUS$.
	  This $ioctl$ can provide \emph {some} information about the current
	  disc that is inserted in the drive.  This functionality used to be
	  implemented in the low level drivers, but is now carried out
	  entirely in \UCD.
	  
	  The history of development of the CD's use as a carrier medium for
	  various digital information has lead to many different disc types.
	  This $ioctl$ is useful only in the case that CDs have \emph {only
	    one} type of data on them.  While this is often the case, it is
	  also very common for CDs to have some tracks with data, and some
	  tracks with audio.  Because this is an existing interface, rather
	  than fixing this interface by changing the assumptions it was made
	  under, thereby breaking all user applications that use this
	  function, the \UCD\ implements this $ioctl$ as follows: If the CD in
	  question has audio tracks on it, and it has absolutely no CD-I, XA,
	  or data tracks on it, it will be reported as $CDS_AUDIO$.  If it has
	  both audio and data tracks, it will return $CDS_MIXED$.  If there
	  are no audio tracks on the disc, and if the CD in question has any
	  CD-I tracks on it, it will be reported as $CDS_XA_2_2$.  Failing
	  that, if the CD in question has any XA tracks on it, it will be
	  reported as $CDS_XA_2_1$.  Finally, if the CD in question has any
	  data tracks on it, it will be reported as a data CD ($CDS_DATA_1$).
	
	  This $ioctl$ can return:
	  $$
	  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
	    CDS_NO_INFO& no information available\cr
	    CDS_NO_DISC& no disc is inserted, or tray is opened\cr
	    CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr
	    CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr
	    CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr
	    CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324  user bytes)\cr
	    CDS_MIXED& mixed audio/data disc\cr
	    }
	  $$
	  For some information concerning frame layout of the various disc
	  types, see a recent version of \cdromh.
	
	\item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a
	  juke-box. 
	\item[CDROMRESET] Reset the drive. 
	\item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the
	  drive. Refer to section \ref{capability} for more information on
	  these flags.
	\item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$
	  unlocks the door, any other value locks it.
	\item[CDROM_DEBUG] Turns on debugging info. Only root is allowed
	  to do this. Same semantics as CDROM_LOCKDOOR.
	\end{description}
	
	\subsubsection{Device dependent $ioctl$s}
	
	Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
	if implemented. No memory allocation or verification is carried out. 
	
	\newsection{How to update your driver}
	
	\begin{enumerate}
	\item Make a backup of your current driver. 
	\item Get hold of the files \cdromc\ and \cdromh, they should be in
	  the directory tree that came with this documentation.
	\item Make sure you include \cdromh.
	\item Change the 3rd argument of $register_blkdev$ from
	$\&<your-drive>_fops$ to $\&cdrom_fops$. 
	\item Just after that line, add the following to register with the \UCD:
	  $$register_cdrom(\&<your-drive>_info);$$
	  Similarly, add a call to $unregister_cdrom()$ at the appropriate place.
	\item Copy an example of the device-operations $struct$ to your
	  source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all
	  entries to names corresponding to your driver, or names you just
	  happen to like. If your driver doesn't support a certain function,
	  make the entry $NULL$. At the entry $capability$ you should list all
	  capabilities your driver currently supports. If your driver
	  has a capability that is not listed, please send me a message.
	\item Copy the $cdrom_device_info$ declaration from the same example
	  driver, and modify the entries according to your needs. If your
	  driver dynamically determines the capabilities of the hardware, this
	  structure should also be declared dynamically. 
	\item Implement all functions in your $<device>_dops$ structure,
	  according to prototypes listed in \cdromh, and specifications given
	  in section~\ref{cdrom.c}. Most likely you have already implemented
	  the code in a large part, and you will almost certainly need to adapt the
	  prototype and return values.
	\item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and
	  change the prototype a little. Remove entries listed in the first
	  part in section~\ref{cdrom-ioctl}, if your code was OK, these are
	  just calls to the routines you adapted in the previous step.
	\item You may remove all remaining memory checking code in the
	  $audio_ioctl()$ function that deals with audio commands (these are
	  listed in the second part of section~\ref{cdrom-ioctl}). There is no
	  need for memory allocation either, so most $case$s in the $switch$
	  statement look similar to:
	  $$
	  case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\ 
	  cdrom_tocentry *{})\ arg\bigr);
	  $$
	\item All remaining $ioctl$ cases must be moved to a separate
	  function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that
	  memory checking and allocation must be kept in this code!
	\item Change the prototypes of $<device>_open()$ and
	  $<device>_release()$, and remove any strategic code (\ie, tray
	  movement, door locking, etc.).
	\item Try to recompile the drivers. We advise you to use modules, both
	  for {\tt {cdrom.o}} and your driver, as debugging is much easier this
	  way.
	\end{enumerate} 
	
	\newsection{Thanks}
	
	Thanks to all the people involved.  First, Erik Andersen, who has
	taken over the torch in maintaining \cdromc\ and integrating much
	\cdrom-related code in the 2.1-kernel.  Thanks to Scott Snyder and
	Gerd Knorr, who were the first to implement this interface for SCSI
	and IDE-CD drivers and added many ideas for extension of the data
	structures relative to kernel~2.0.  Further thanks to Heiko Ei{\sz}feldt,
	Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
	Kroll, the \linux\ \cdrom\ device driver developers who were kind
	enough to give suggestions and criticisms during the writing. Finally
	of course, I want to thank Linus Torvalds for making this possible in
	the first place.
	
	\vfill
	$ \version\ $
	\eject
	\end{document}

• [ cdrom ]
• 00-INDEX
• cdrom-standard.tex
• ide-cd
• Makefile
• packet-writing.txt
•