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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:54 EST.

1	\documentclass{article}
2	\def\version{$Id: cdrom-standard.tex,v 1.9 1997/12/28 15:42:49 david Exp $}
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9	
10	\def\linux{{\sc Linux}}
11	\def\cdrom{{\sc cd-rom}}
12	\def\UCD{{\sc Uniform cd-rom Driver}}
13	\def\cdromc{{\tt {cdrom.c}}}
14	\def\cdromh{{\tt {cdrom.h}}}
15	\def\fo{\sl}                    % foreign words
16	\def\ie{{\fo i.e.}}
17	\def\eg{{\fo e.g.}}
18	
19	\everymath{\it} \everydisplay{\it}
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22	
23	\begin{document}
24	\title{A \linux\ \cdrom\ standard}
25	\author{David van Leeuwen\\{\normalsize\tt david@ElseWare.cistron.nl}
26	\\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}}
27	\\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}}
28	\date{12 March 1999}
29	
30	\maketitle
31	
32	\newsection{Introduction}
33	
34	\linux\ is probably the Unix-like operating system that supports
35	the widest variety of hardware devices. The reasons for this are
36	presumably 
37	\begin{itemize} 
38	\item 
39	  The large list of hardware devices available for the many platforms
40	  that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.)
41	\item 
42	  The open design of the operating system, such that anybody can write a
43	  driver for \linux.
44	\item 
45	  There is plenty of source code around as examples of how to write a driver.
46	\end{itemize}
47	The openness of \linux, and the many different types of available
48	hardware has allowed \linux\ to support many different hardware devices.
49	Unfortunately, the very openness that has allowed \linux\ to support
50	all these different devices has also allowed the behavior of each
51	device driver to differ significantly from one device to another.
52	This divergence of behavior has been very significant for \cdrom\
53	devices; the way a particular drive reacts to a `standard' $ioctl()$
54	call varies greatly from one device driver to another. To avoid making
55	their drivers totally inconsistent, the writers of \linux\ \cdrom\
56	drivers generally created new device drivers by understanding, copying,
57	and then changing an existing one. Unfortunately, this practice did not
58	maintain uniform behavior across all the \linux\ \cdrom\ drivers. 
59	
60	This document describes an effort to establish Uniform behavior across
61	all the different \cdrom\ device drivers for \linux. This document also
62	defines the various $ioctl$s, and how the low-level \cdrom\ device
63	drivers should implement them. Currently (as of the \linux\ 2.1.$x$
64	development kernels) several low-level \cdrom\ device drivers, including
65	both IDE/ATAPI and SCSI, now use this Uniform interface.
66	
67	When the \cdrom\ was developed, the interface between the \cdrom\ drive
68	and the computer was not specified in the standards. As a result, many
69	different \cdrom\ interfaces were developed. Some of them had their
70	own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
71	manufacturers adopted an existing electrical interface and changed
72	the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
73	adapted their drives to one or more of the already existing electrical
74	interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
75	most of the `NoName' manufacturers). In cases where a new drive really
76	brought its own interface or used its own command set and flow control
77	scheme, either a separate driver had to be written, or an existing
78	driver had to be enhanced. History has delivered us \cdrom\ support for
79	many of these different interfaces. Nowadays, almost all new \cdrom\
80	drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
81	manufacturer will create a new interface. Even finding drives for the
82	old proprietary interfaces is getting difficult.
83	
84	When (in the 1.3.70's) I looked at the existing software interface,
85	which was expressed through \cdromh, it appeared to be a rather wild
86	set of commands and data formats.\footnote{I cannot recollect what
87	kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
88	latest kernel that I was indirectly involved in.} It seemed that many
89	features of the software interface had been added to accommodate the
90	capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
91	importantly, it appeared that the behavior of the `standard' commands
92	was different for most of the different drivers: \eg, some drivers
93	close the tray if an $open()$ call occurs when the tray is open, while
94	others do not. Some drivers lock the door upon opening the device, to
95	prevent an incoherent file system, but others don't, to allow software
96	ejection. Undoubtedly, the capabilities of the different drives vary,
97	but even when two drives have the same capability their drivers'
98	behavior was usually different.
99	
100	I decided to start a discussion on how to make all the \linux\ \cdrom\
101	drivers behave more uniformly. I began by contacting the developers of
102	the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
103	encouraged me to write the \UCD\ which this document is intended to
104	describe. The implementation of the \UCD\ is in the file \cdromc. This
105	driver is intended to be an additional software layer that sits on top
106	of the low-level device drivers for each \cdrom\ drive. By adding this
107	additional layer, it is possible to have all the different \cdrom\
108	devices behave {\em exactly\/} the same (insofar as the underlying
109	hardware will allow).
110	
111	The goal of the \UCD\ is {\em not\/} to alienate driver developers who
112	have not yet taken steps to support this effort. The goal of \UCD\ is
113	simply to give people writing application programs for \cdrom\ drives
114	{\em one\/} \linux\ \cdrom\ interface with consistent behavior for all
115	\cdrom\ devices. In addition, this also provides a consistent interface
116	between the low-level device driver code and the \linux\ kernel. Care
117	is taken that 100\,\% compatibility exists with the data structures and
118	programmer's interface defined in \cdromh. This guide was written to
119	help \cdrom\ driver developers adapt their code to use the \UCD\ code
120	defined in \cdromc.
121	
122	Personally, I think that the most important hardware interfaces are
123	the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
124	of hardware drop continuously, it is also likely that people may have
125	more than one \cdrom\ drive, possibly of mixed types. It is important
126	that these drives behave in the same way. In December 1994, one of the
127	cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
128	drive. In the months that I was busy writing a \linux\ driver for it,
129	proprietary drives became obsolete and IDE/ATAPI drives became the
130	standard. At the time of the last update to this document (November
131	1997) it is becoming difficult to even {\em find} anything less than a
132	16 speed \cdrom\ drive, and 24 speed drives are common.
133	
134	\newsection{Standardizing through another software level}
135	\label{cdrom.c}
136	
137	At the time this document was conceived, all drivers directly
138	implemented the \cdrom\ $ioctl()$ calls through their own routines. This
139	led to the danger of different drivers forgetting to do important things
140	like checking that the user was giving the driver valid data. More
141	importantly, this led to the divergence of behavior, which has already
142	been discussed.
143	
144	For this reason, the \UCD\ was created to enforce consistent \cdrom\
145	drive behavior, and to provide a common set of services to the various
146	low-level \cdrom\ device drivers. The \UCD\ now provides another
147	software-level, that separates the $ioctl()$ and $open()$ implementation
148	from the actual hardware implementation. Note that this effort has
149	made few changes which will affect a user's application programs. The
150	greatest change involved moving the contents of the various low-level
151	\cdrom\ drivers' header files to the kernel's cdrom directory. This was
152	done to help ensure that the user is only presented with only one cdrom
153	interface, the interface defined in \cdromh.
154	
155	\cdrom\ drives are specific enough (\ie, different from other
156	block-devices such as floppy or hard disc drives), to define a set
157	of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
158	These operations are different from the classical block-device file
159	operations, $<block-device>_fops$.
160	
161	The routines for the \UCD\ interface level are implemented in the file
162	\cdromc. In this file, the \UCD\ interfaces with the kernel as a block
163	device by registering the following general $struct\ file_operations$:
164	$$
165	\halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
166	struct& file_operations\ cdrom_fops = \{\hidewidth\cr
167	        &NULL,                  & lseek \cr
168	        &block_read,            & read---general block-dev read \cr
169	        &block_write,           & write---general block-dev write \cr
170	        &NULL,                  & readdir \cr
171	        &NULL,                  & select \cr
172	        &cdrom_ioctl,           & ioctl \cr
173	        &NULL,                  & mmap \cr
174	        &cdrom_open,            & open \cr
175	        &cdrom_release,         & release \cr
176	        &NULL,                  & fsync \cr
177	        &NULL,                  & fasync \cr
178	        &cdrom_media_changed,   & media change \cr
179	        &NULL                   & revalidate \cr
180	\};\cr
181	}
182	$$ 
183	
184	Every active \cdrom\ device shares this $struct$. The routines
185	declared above are all implemented in \cdromc, since this file is the
186	place where the behavior of all \cdrom-devices is defined and
187	standardized. The actual interface to the various types of \cdrom\ 
188	hardware is still performed by various low-level \cdrom-device
189	drivers. These routines simply implement certain {\em capabilities\/}
190	that are common to all \cdrom\ (and really, all removable-media
191	devices).
192	
193	Registration of a low-level \cdrom\ device driver is now done through
194	the general routines in \cdromc, not through the Virtual File System
195	(VFS) any more. The interface implemented in \cdromc\ is carried out
196	through two general structures that contain information about the
197	capabilities of the driver, and the specific drives on which the
198	driver operates. The structures are:
199	\begin{description}
200	\item[$cdrom_device_ops$] 
201	  This structure contains information about the low-level driver for a
202	  \cdrom\ device. This structure is conceptually connected to the major
203	  number of the device (although some drivers may have different
204	  major numbers, as is the case for the IDE driver).
205	\item[$cdrom_device_info$] 
206	  This structure contains information about a particular \cdrom\ drive,
207	  such as its device name, speed, etc. This structure is conceptually
208	  connected to the minor number of the device.
209	\end{description}
210	
211	Registering a particular \cdrom\ drive with the \UCD\ is done by the
212	low-level device driver though a call to:
213	$$register_cdrom(struct\ cdrom_device_info * <device>_info)  
214	$$
215	The device information structure, $<device>_info$, contains all the
216	information needed for the kernel to interface with the low-level
217	\cdrom\ device driver. One of the most important entries in this
218	structure is a pointer to the $cdrom_device_ops$ structure of the
219	low-level driver.
220	
221	The device operations structure, $cdrom_device_ops$, contains a list
222	of pointers to the functions which are implemented in the low-level
223	device driver. When \cdromc\ accesses a \cdrom\ device, it does it
224	through the functions in this structure. It is impossible to know all
225	the capabilities of future \cdrom\ drives, so it is expected that this
226	list may need to be expanded from time to time as new technologies are
227	developed. For example, CD-R and CD-R/W drives are beginning to become
228	popular, and support will soon need to be added for them. For now, the
229	current $struct$ is:
230	$$
231	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
232	  $/*$ \rm# $*/$\hfil\cr
233	struct& cdrom_device_ops\ \{ \hidewidth\cr
234	  &int& (* open)(struct\ cdrom_device_info *, int)\cr
235	  &void& (* release)(struct\ cdrom_device_info *);\cr 
236	  &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr     
237	  &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 
238	  &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
239	  &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
240	  &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
241	  &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
242	  &int& (* get_last_session) (struct\ cdrom_device_info *, 
243	        struct\ cdrom_multisession *{});\cr
244	  &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
245	  &int& (* reset)(struct\ cdrom_device_info *);\cr
246	  &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
247	        void *{});\cr 
248	  &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
249	        unsigned\ long);\cr
250	\noalign{\medskip}
251	  &const\ int& capability;& capability flags \cr
252	\};\cr
253	}
254	$$
255	When a low-level device driver implements one of these capabilities,
256	it should add a function pointer to this $struct$. When a particular
257	function is not implemented, however, this $struct$ should contain a
258	NULL instead. The $capability$ flags specify the capabilities of the
259	\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
260	is registered with the \UCD.
261	
262	Note that most functions have fewer parameters than their
263	$blkdev_fops$ counterparts. This is because very little of the
264	information in the structures $inode$ and $file$ is used. For most
265	drivers, the main parameter is the $struct$ $cdrom_device_info$, from
266	which the major and minor number can be extracted. (Most low-level
267	\cdrom\ drivers don't even look at the major and minor number though,
268	since many of them only support one device.) This will be available
269	through $dev$ in $cdrom_device_info$ described below.
270	
271	The drive-specific, minor-like information that is registered with
272	\cdromc, currently contains the following fields:
273	$$
274	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
275	  $/*$ \rm# $*/$\hfil\cr
276	struct& cdrom_device_info\ \{ \hidewidth\cr
277	  & struct\ cdrom_device_ops *& ops;& device operations for this major\cr
278	  & struct\ cdrom_device_info *& next;& next device_info for this major\cr
279	  & void *&  handle;& driver-dependent data\cr
280	\noalign{\medskip}
281	  & kdev_t&  dev;& device number (incorporates minor)\cr
282	  & int& mask;& mask of capability: disables them \cr
283	  & int& speed;& maximum speed for reading data \cr
284	  & int& capacity;& number of discs in a jukebox \cr
285	\noalign{\medskip}
286	  &int& options : 30;& options flags \cr
287	  &unsigned& mc_flags : 2;& media-change buffer flags \cr
288	  & int& use_count;& number of times device is opened\cr
289	  & char& name[20];& name of the device type\cr
290	\}\cr
291	}$$
292	Using this $struct$, a linked list of the registered minor devices is
293	built, using the $next$ field. The device number, the device operations
294	struct and specifications of properties of the drive are stored in this
295	structure.
296	
297	The $mask$ flags can be used to mask out some of the capabilities listed
298	in $ops\to capability$, if a specific drive doesn't support a feature
299	of the driver. The value $speed$ specifies the maximum head-rate of the
300	drive, measured in units of normal audio speed (176\,kB/sec raw data or
301	150\,kB/sec file system data). The value $n_discs$ should reflect the
302	number of discs the drive can hold simultaneously, if it is designed
303	as a juke-box, or otherwise~1. The parameters are declared $const$
304	because they describe properties of the drive, which don't change after
305	registration.
306	
307	A few registers contain variables local to the \cdrom\ drive. The
308	flags $options$ are used to specify how the general \cdrom\ routines
309	should behave. These various flags registers should provide enough
310	flexibility to adapt to the different users' wishes (and {\em not\/} the
311	`arbitrary' wishes of the author of the low-level device driver, as is
312	the case in the old scheme). The register $mc_flags$ is used to buffer
313	the information from $media_changed()$ to two separate queues. Other
314	data that is specific to a minor drive, can be accessed through $handle$,
315	which can point to a data structure specific to the low-level driver.
316	The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
317	initialized.
318	
319	The intermediate software layer that \cdromc\ forms will perform some
320	additional bookkeeping. The use count of the device (the number of
321	processes that have the device opened) is registered in $use_count$. The
322	function $cdrom_ioctl()$ will verify the appropriate user-memory regions
323	for read and write, and in case a location on the CD is transferred,
324	it will `sanitize' the format by making requests to the low-level
325	drivers in a standard format, and translating all formats between the
326	user-software and low level drivers. This relieves much of the drivers'
327	memory checking and format checking and translation. Also, the necessary
328	structures will be declared on the program stack.
329	
330	The implementation of the functions should be as defined in the
331	following sections. Two functions {\em must\/} be implemented, namely
332	$open()$ and $release()$. Other functions may be omitted, their
333	corresponding capability flags will be cleared upon registration.
334	Generally, a function returns zero on success and negative on error. A
335	function call should return only after the command has completed, but of
336	course waiting for the device should not use processor time.
337	
338	\subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
339	
340	$Open()$ should try to open the device for a specific $purpose$, which
341	can be either:
342	\begin{itemize}
343	\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
344	user commands {\tt {dd}} or {\tt {cat}}.  
345	\item[1] Open for $ioctl$ commands, as done by audio-CD playing
346	programs.
347	\end{itemize}
348	Notice that any strategic code (closing tray upon $open()$, etc.)\ is
349	done by the calling routine in \cdromc, so the low-level routine
350	should only be concerned with proper initialization, such as spinning
351	up the disc, etc. % and device-use count
352	
353	
354	\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
355	
356	
357	Device-specific actions should be taken such as spinning down the device.
358	However, strategic actions such as ejection of the tray, or unlocking
359	the door, should be left over to the general routine $cdrom_release()$.
360	This is the only function returning type $void$.
361	
362	\subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
363	\label{drive status}
364	
365	The function $drive_status$, if implemented, should provide
366	information on the status of the drive (not the status of the disc,
367	which may or may not be in the drive). If the drive is not a changer,
368	$slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 
369	$$
370	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
371	CDS_NO_INFO& no information available\cr
372	CDS_NO_DISC& no disc is inserted, tray is closed\cr
373	CDS_TRAY_OPEN& tray is opened\cr
374	CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
375	CDS_DISC_OK& a disc is loaded and everything is fine\cr
376	}
377	$$
378	
379	\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
380	
381	This function is very similar to the original function in $struct\ 
382	file_operations$. It returns 1 if the medium of the device $cdi\to
383	dev$ has changed since the last call, and 0 otherwise. The parameter
384	$disc_nr$ identifies a specific slot in a juke-box, it should be
385	ignored for single-disc drives.  Note that by `re-routing' this
386	function through $cdrom_media_changed()$, we can implement separate
387	queues for the VFS and a new $ioctl()$ function that can report device
388	changes to software (\eg, an auto-mounting daemon).
389	
390	\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
391	
392	This function, if implemented, should control the tray movement. (No
393	other function should control this.) The parameter $position$ controls
394	the desired direction of movement:
395	\begin{itemize}
396	\item[0] Close tray
397	\item[1] Open tray
398	\end{itemize}
399	This function returns 0 upon success, and a non-zero value upon
400	error. Note that if the tray is already in the desired position, no
401	action need be taken, and the return value should be 0. 
402	
403	\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
404	
405	This function (and no other code) controls locking of the door, if the
406	drive allows this. The value of $lock$ controls the desired locking
407	state:
408	\begin{itemize}
409	\item[0] Unlock door, manual opening is allowed
410	\item[1] Lock door, tray cannot be ejected manually
411	\end{itemize}
412	This function returns 0 upon success, and a non-zero value upon
413	error. Note that if the door is already in the requested state, no
414	action need be taken, and the return value should be 0. 
415	
416	\subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
417	
418	Some \cdrom\ drives are capable of changing their head-speed. There
419	are several reasons for changing the speed of a \cdrom\ drive. Badly
420	pressed \cdrom s may benefit from less-than-maximum head rate. Modern
421	\cdrom\ drives can obtain very high head rates (up to $24\times$ is
422	common).  It has been reported that these drives can make reading
423	errors at these high speeds, reducing the speed can prevent data loss
424	in these circumstances.  Finally, some of these drives can
425	make an annoyingly loud noise, which a lower speed may reduce. %Finally,
426	%although the audio-low-pass filters probably aren't designed for it,
427	%more than real-time playback of audio might be used for high-speed
428	%copying of audio tracks.
429	
430	This function specifies the speed at which data is read or audio is
431	played back. The value of $speed$ specifies the head-speed of the
432	drive, measured in units of standard cdrom speed (176\,kB/sec raw data
433	or 150\,kB/sec file system data). So to request that a \cdrom\ drive
434	operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
435	with $speed=2$. The special value `0' means `auto-selection', \ie,
436	maximum data-rate or real-time audio rate. If the drive doesn't have
437	this `auto-selection' capability, the decision should be made on the
438	current disc loaded and the return value should be positive. A negative
439	return value indicates an error.
440	
441	\subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
442	
443	If the drive can store multiple discs (a juke-box) this function
444	will perform disc selection. It should return the number of the
445	selected disc on success, a negative value on error. Currently, only
446	the ide-cd driver supports this functionality.
447	
448	\subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\
449	  cdrom_multisession * ms_info)$}
450	
451	This function should implement the old corresponding $ioctl()$. For
452	device $cdi\to dev$, the start of the last session of the current disc
453	should be returned in the pointer argument $ms_info$. Note that
454	routines in \cdromc\ have sanitized this argument: its requested
455	format will {\em always\/} be of the type $CDROM_LBA$ (linear block
456	addressing mode), whatever the calling software requested. But
457	sanitization goes even further: the low-level implementation may
458	return the requested information in $CDROM_MSF$ format if it wishes so
459	(setting the $ms_info\rightarrow addr_format$ field appropriately, of
460	course) and the routines in \cdromc\ will make the transformation if
461	necessary. The return value is 0 upon success.
462	
463	\subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
464	  cdrom_mcn * mcn)$}
465	
466	Some discs carry a `Media Catalog Number' (MCN), also called
467	`Universal Product Code' (UPC). This number should reflect the number
468	that is generally found in the bar-code on the product. Unfortunately,
469	the few discs that carry such a number on the disc don't even use the
470	same format. The return argument to this function is a pointer to a
471	pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
472	expected as a 13-character string, terminated by a null-character.
473	
474	\subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
475	
476	This call should perform a hard-reset on the drive (although in
477	circumstances that a hard-reset is necessary, a drive may very well not
478	listen to commands anymore). Preferably, control is returned to the
479	caller only after the drive has finished resetting. If the drive is no
480	longer listening, it may be wise for the underlying low-level cdrom
481	driver to time out.
482	
483	\subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
484	  int\ cmd, void * arg)$}
485	
486	Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
487	implemented by the routines described above, and hence the function
488	$cdrom_ioctl$ will use those. However, most $ioctl$s deal with
489	audio-control. We have decided to leave these to be accessed through a
490	single function, repeating the arguments $cmd$ and $arg$. Note that
491	the latter is of type $void*{}$, rather than $unsigned\ long\
492	int$. The routine $cdrom_ioctl()$ does do some useful things,
493	though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
494	Seconds, Frames) for all audio calls. It also verifies the memory
495	location of $arg$, and reserves stack-memory for the argument. This
496	makes implementation of the $audio_ioctl()$ much simpler than in the
497	old driver scheme. For example, you may look up the function
498	$cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
499	this documentation. 
500	
501	An unimplemented ioctl should return $-ENOSYS$, but a harmless request
502	(\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
503	errors should be according to the standards, whatever they are. When
504	an error is returned by the low-level driver, the \UCD\ tries whenever
505	possible to return the error code to the calling program. (We may decide
506	to sanitize the return value in $cdrom_ioctl()$ though, in order to
507	guarantee a uniform interface to the audio-player software.)
508	
509	\subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\
510	  cmd, unsigned\ long\ arg)$}
511	
512	Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
513	they are introduced to service some capabilities of certain drives. In
514	fact, there are 6 different $ioctl$s for reading data, either in some
515	particular kind of format, or audio data. Not many drives support
516	reading audio tracks as data, I believe this is because of protection
517	of copyrights of artists. Moreover, I think that if audio-tracks are
518	supported, it should be done through the VFS and not via $ioctl$s. A
519	problem here could be the fact that audio-frames are 2352 bytes long,
520	so either the audio-file-system should ask for 75264 bytes at once
521	(the least common multiple of 512 and 2352), or the drivers should
522	bend their backs to cope with this incoherence (to which I would be
523	opposed).  Furthermore, it is very difficult for the hardware to find
524	the exact frame boundaries, since there are no synchronization headers
525	in audio frames.  Once these issues are resolved, this code should be
526	standardized in \cdromc.
527	
528	Because there are so many $ioctl$s that seem to be introduced to
529	satisfy certain drivers,\footnote{Is there software around that
530	  actually uses these? I'd be interested!} any `non-standard' $ioctl$s
531	are routed through the call $dev_ioctl()$. In principle, `private'
532	$ioctl$s should be numbered after the device's major number, and not
533	the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
534	non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2,
535	  CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK,
536	  CDROMPLAY\-BLK and CDROM\-READALL}.
537	
538	
539	\subsection{\cdrom\ capabilities}
540	\label{capability}
541	
542	Instead of just implementing some $ioctl$ calls, the interface in
543	\cdromc\ supplies the possibility to indicate the {\em capabilities\/}
544	of a \cdrom\ drive. This can be done by ORing any number of
545	capability-constants that are defined in \cdromh\ at the registration
546	phase. Currently, the capabilities are any of:
547	$$
548	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
549	CDC_CLOSE_TRAY& can close tray by software control\cr
550	CDC_OPEN_TRAY& can open tray\cr
551	CDC_LOCK& can lock and unlock the door\cr
552	CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
553	CDC_SELECT_DISC& drive is juke-box\cr
554	CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
555	CDC_MCN& can read Media Catalog Number\cr
556	CDC_MEDIA_CHANGED& can report if disc has changed\cr
557	CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
558	CDC_RESET& hard reset device\cr
559	CDC_IOCTLS& driver has non-standard ioctls\cr
560	CDC_DRIVE_STATUS& driver implements drive status\cr
561	}
562	$$
563	The capability flag is declared $const$, to prevent drivers from
564	accidentally tampering with the contents. The capability fags actually
565	inform \cdromc\ of what the driver can do. If the drive found
566	by the driver does not have the capability, is can be masked out by
567	the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
568	driver has implemented the code for loading and ejecting \cdrom's, and
569	hence its corresponding flags in $capability$ will be set. But a SCSI
570	\cdrom\ drive might be a caddy system, which can't load the tray, and
571	hence for this drive the $cdrom_device_info$ struct will have set
572	the $CDC_CLOSE_TRAY$ bit in $mask$.
573	
574	In the file \cdromc\ you will encounter many constructions of the type
575	$$\it
576	if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 
577	   \mathrel{\&} CDC_<capability>) \ldots
578	$$
579	There is no $ioctl$ to set the mask\dots The reason is that
580	I think it is better to control the {\em behavior\/} rather than the
581	{\em capabilities}.
582	
583	\subsection{Options}
584	
585	A final flag register controls the {\em behavior\/} of the \cdrom\
586	drives, in order to satisfy different users' wishes, hopefully
587	independently of the ideas of the respective author who happened to
588	have made the drive's support available to the \linux\ community. The
589	current behavior options are:
590	$$
591	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
592	CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
593	CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
594	CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
595	 purpose for $open()$\cr
596	CDO_LOCK& try to lock door if device is opened\cr
597	CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
598	}
599	$$
600	
601	The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
602	CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
603	interface and software standards. Before you protest, there are two
604	new $ioctl$s implemented in \cdromc, that allow you to control the
605	behavior by software. These are:
606	$$
607	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
608	CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
609	CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
610	}
611	$$
612	One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
613	newsection we explain what the need for this option is.
614	
615	A software package {\tt setcd}, available from the Debian distribution
616	and {\tt sunsite.unc.edu}, allows user level control of these flags. 
617	
618	\newsection{The need to know the purpose of opening the \cdrom\ device}
619	
620	Traditionally, Unix devices can be used in two different `modes',
621	either by reading/writing to the device file, or by issuing
622	controlling commands to the device, by the device's $ioctl()$
623	call. The problem with \cdrom\ drives, is that they can be used for
624	two entirely different purposes. One is to mount removable
625	file systems, \cdrom s, the other is to play audio CD's. Audio commands
626	are implemented entirely through $ioctl$s, presumably because the
627	first implementation (SUN?) has been such. In principle there is
628	nothing wrong with this, but a good control of the `CD player' demands
629	that the device can {\em always\/} be opened in order to give the
630	$ioctl$ commands, regardless of the state the drive is in. 
631	
632	On the other hand, when used as a removable-media disc drive (what the
633	original purpose of \cdrom s is) we would like to make sure that the
634	disc drive is ready for operation upon opening the device. In the old
635	scheme, some \cdrom\ drivers don't do any integrity checking, resulting
636	in a number of i/o errors reported by the VFS to the kernel when an
637	attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
638	particularly elegant way to find out that there is no \cdrom\ inserted;
639	it more-or-less looks like the old IBM-PC trying to read an empty floppy
640	drive for a couple of seconds, after which the system complains it
641	can't read from it. Nowadays we can {\em sense\/} the existence of a
642	removable medium in a drive, and we believe we should exploit that
643	fact. An integrity check on opening of the device, that verifies the
644	availability of a \cdrom\ and its correct type (data), would be
645	desirable.
646	
647	These two ways of using a \cdrom\ drive, principally for data and
648	secondarily for playing audio discs, have different demands for the
649	behavior of the $open()$ call. Audio use simply wants to open the
650	device in order to get a file handle which is needed for issuing
651	$ioctl$ commands, while data use wants to open for correct and
652	reliable data transfer. The only way user programs can indicate what
653	their {\em purpose\/} of opening the device is, is through the $flags$
654	parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
655	implemented (some drivers implement checking for write-related flags,
656	but this is not strictly necessary if the device file has correct
657	permission flags). Most option flags simply don't make sense to
658	\cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and
659	$O_SYNC$ have no meaning to a \cdrom. 
660	
661	We therefore propose to use the flag $O_NONBLOCK$ to indicate
662	that the device is opened just for issuing $ioctl$
663	commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
664	subsequent calls to the device don't cause the calling process to
665	wait. We could interpret this as ``don't wait until someone has
666	inserted some valid data-\cdrom.'' Thus, our proposal of the
667	implementation for the $open()$ call for \cdrom s is:
668	\begin{itemize}
669	\item If no other flags are set than $O_RDONLY$, the device is opened
670	for data transfer, and the return value will be 0 only upon successful
671	initialization of the transfer. The call may even induce some actions
672	on the \cdrom, such as closing the tray.  
673	\item If the option flag $O_NONBLOCK$ is set, opening will always be
674	successful, unless the whole device doesn't exist. The drive will take
675	no actions whatsoever. 
676	\end{itemize}
677	
678	\subsection{And what about standards?}
679	
680	You might hesitate to accept this proposal as it comes from the
681	\linux\ community, and not from some standardizing institute. What
682	about SUN, SGI, HP and all those other Unix and hardware vendors?
683	Well, these companies are in the lucky position that they generally
684	control both the hardware and software of their supported products,
685	and are large enough to set their own standard. They do not have to
686	deal with a dozen or more different, competing hardware
687	configurations.\footnote{Incidentally, I think that SUN's approach to
688	mounting \cdrom s is very good in origin: under Solaris a
689	volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
690	{/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
691	further and have {\em every\/} \cdrom\ on the local area network be
692	mounted at the similar location, \ie, no matter in which particular
693	machine you insert a \cdrom, it will always appear at the same
694	position in the directory tree, on every system. When I wanted to
695	implement such a user-program for \linux, I came across the
696	differences in behavior of the various drivers, and the need for an
697	$ioctl$ informing about media changes.}
698	
699	We believe that using $O_NONBLOCK$ to indicate that a device is being opened
700	for $ioctl$ commands only can be easily introduced in the \linux\
701	community. All the CD-player authors will have to be informed, we can
702	even send in our own patches to the programs. The use of $O_NONBLOCK$
703	has most likely no influence on the behavior of the CD-players on
704	other operating systems than \linux. Finally, a user can always revert
705	to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
706	CDO_USE_FFLAGS)$. 
707	
708	\subsection{The preferred strategy of $open()$}
709	
710	The routines in \cdromc\ are designed in such a way that run-time
711	configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
712	can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
713	modes of operation can be set:
714	\begin{description}
715	\item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
716	is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
717	future.) If the device is not yet opened by any other process, and if
718	the device is being opened for data ($O_NONBLOCK$ is not set) and the
719	tray is found to be open, an attempt to close the tray is made. Then,
720	it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
721	set, that it contains tracks of type `data mode 1.' Only if all tests
722	are passed is the return value zero. The door is locked to prevent file
723	system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
724	set), no actions are taken and a value of 0 will be returned. 
725	\item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This
726	mimics the behavior of the current sbpcd-driver. The option flags are
727	ignored, the tray is closed on the first open, if necessary. Similarly,
728	the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
729	it is automatically ejected, such that the user can replace it.
730	\end{description} 
731	We hope that these option can convince everybody (both driver
732	maintainers and user program developers) to adopt the new \cdrom\
733	driver scheme and option flag interpretation.
734	
735	\newsection{Description of routines in \cdromc}
736	
737	Only a few routines in \cdromc\ are exported to the drivers. In this
738	new section we will discuss these, as well as the functions that `take
739	over' the \cdrom\ interface to the kernel. The header file belonging
740	to \cdromc\ is called \cdromh. Formerly, some of the contents of this
741	file were placed in the file {\tt {ucdrom.h}}, but this file has now been
742	merged back into \cdromh.
743	
744	\subsection{$Struct\ file_operations\ cdrom_fops$}
745	
746	The contents of this structure were described in section~\ref{cdrom.c}.
747	A pointer to this structure is assigned to the $fops$ field
748	of the $struct gendisk$.
749	
750	\subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
751	
752	This function is used in about the same way one registers $cdrom_fops$
753	with the kernel, the device operations and information structures,
754	as described in section~\ref{cdrom.c}, should be registered with the
755	\UCD:
756	$$
757	register_cdrom(\&<device>_info));
758	$$
759	This function returns zero upon success, and non-zero upon
760	failure. The structure $<device>_info$ should have a pointer to the
761	driver's $<device>_dops$, as in 
762	$$
763	\vbox{\halign{&$#$\hfil\cr
764	struct\ &cdrom_device_info\ <device>_info = \{\cr
765	& <device>_dops;\cr
766	&\ldots\cr
767	\}\cr
768	}}$$
769	Note that a driver must have one static structure, $<device>_dops$, while
770	it may have as many structures $<device>_info$ as there are minor devices
771	active. $Register_cdrom()$ builds a linked list from these. 
772	
773	\subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
774	
775	Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
776	the minor device from the list. If it was the last registered minor for
777	the low-level driver, this disconnects the registered device-operation
778	routines from the \cdrom\ interface. This function returns zero upon
779	success, and non-zero upon failure.
780	
781	\subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
782	
783	This function is not called directly by the low-level drivers, it is
784	listed in the standard $cdrom_fops$. If the VFS opens a file, this
785	function becomes active. A strategy is implemented in this routine,
786	taking care of all capabilities and options that are set in the
787	$cdrom_device_ops$ connected to the device. Then, the program flow is
788	transferred to the device_dependent $open()$ call.
789	
790	\subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
791	*fp)$}
792	
793	This function implements the reverse-logic of $cdrom_open()$, and then
794	calls the device-dependent $release()$ routine. When the use-count has
795	reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
796	and $invalidate_buffers(dev)$.
797	
798	
799	\subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
800	unsigned\ int\ cmd, unsigned\ long\ arg)$}
801	\label{cdrom-ioctl}
802	
803	This function handles all the standard $ioctl$ requests for \cdrom\
804	devices in a uniform way. The different calls fall into three
805	categories: $ioctl$s that can be directly implemented by device
806	operations, ones that are routed through the call $audio_ioctl()$, and
807	the remaining ones, that are presumable device-dependent. Generally, a
808	negative return value indicates an error.
809	
810	\subsubsection{Directly implemented $ioctl$s}
811	\label{ioctl-direct}
812	
813	The following `old' \cdrom-$ioctl$s are implemented by directly
814	calling device-operations in $cdrom_device_ops$, if implemented and
815	not masked:
816	\begin{description}
817	\item[CDROMMULTISESSION] Requests the last session on a \cdrom.
818	\item[CDROMEJECT] Open tray. 
819	\item[CDROMCLOSETRAY] Close tray.
820	\item[CDROMEJECT_SW] If $arg\not=0$, set behavior to auto-close (close
821	tray on first open) and auto-eject (eject on last release), otherwise
822	set behavior to non-moving on $open()$ and $release()$ calls.
823	\item[CDROM_GET_MCN] Get the Media Catalog Number from a CD.
824	\end{description}
825	
826	\subsubsection{$Ioctl$s routed through $audio_ioctl()$}
827	\label{ioctl-audio}
828	
829	The following set of $ioctl$s are all implemented through a call to
830	the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
831	allocation are performed in $cdrom_ioctl()$, and also sanitization of
832	address format ($CDROM_LBA$/$CDROM_MSF$) is done.
833	\begin{description}
834	\item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
835	cdrom_subchnl *{}$.
836	\item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type
837	$struct\ cdrom_tochdr *{}$. 
838	\item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and
839	specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
840	\item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
841	Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
842	\item[CDROMPLAYTRKIND] Play audio fragment in track-index format
843	delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
844	\item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
845	cdrom_volctrl *{}$.
846	\item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
847	cdrom_volctrl *{}$.
848	\item[CDROMSTART] Spin up disc.
849	\item[CDROMSTOP] Stop playback of audio fragment.
850	\item[CDROMPAUSE] Pause playback of audio fragment.
851	\item[CDROMRESUME] Resume playing.
852	\end{description}
853	
854	\subsubsection{New $ioctl$s in \cdromc}
855	
856	The following $ioctl$s have been introduced to allow user programs to
857	control the behavior of individual \cdrom\ devices. New $ioctl$
858	commands can be identified by the underscores in their names.
859	\begin{description}
860	\item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
861	option flag register after modification. Use  $arg = \rm0$ for reading
862	the current flags.
863	\item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns
864	  the option flag register after modification.
865	\item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as
866	  by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or
867	  150\,kB/sec file system data). The value 0 means `auto-select', \ie,
868	  play audio discs at real time and data discs at maximum speed. The value
869	  $arg$ is checked against the maximum head rate of the drive found in the
870	  $cdrom_dops$.
871	\item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box.
872	  First disc is numbered 0. The number $arg$ is checked against the
873	  maximum number of discs in the juke-box found in the $cdrom_dops$.
874	\item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since
875	  the last call. Note that calls to $cdrom_media_changed$ by the VFS
876	  are treated by an independent queue, so both mechanisms will detect
877	  a media change once. For juke-boxes, an extra argument $arg$
878	  specifies the slot for which the information is given. The special
879	  value $CDSL_CURRENT$ requests that information about the currently
880	  selected slot be returned.
881	\item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to
882	  $drive_status()$. Return values are defined in section~\ref{drive
883	   status}. Note that this call doesn't return information on the
884	  current playing activity of the drive; this can be polled through an
885	  $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument
886	  $arg$ specifies the slot for which (possibly limited) information is
887	  given. The special value $CDSL_CURRENT$ requests that information
888	  about the currently selected slot be returned.
889	\item[CDROM_DISC_STATUS] Returns the type of the disc currently in the
890	  drive.  It should be viewed as a complement to $CDROM_DRIVE_STATUS$.
891	  This $ioctl$ can provide \emph {some} information about the current
892	  disc that is inserted in the drive.  This functionality used to be
893	  implemented in the low level drivers, but is now carried out
894	  entirely in \UCD.
895	  
896	  The history of development of the CD's use as a carrier medium for
897	  various digital information has lead to many different disc types.
898	  This $ioctl$ is useful only in the case that CDs have \emph {only
899	    one} type of data on them.  While this is often the case, it is
900	  also very common for CDs to have some tracks with data, and some
901	  tracks with audio.  Because this is an existing interface, rather
902	  than fixing this interface by changing the assumptions it was made
903	  under, thereby breaking all user applications that use this
904	  function, the \UCD\ implements this $ioctl$ as follows: If the CD in
905	  question has audio tracks on it, and it has absolutely no CD-I, XA,
906	  or data tracks on it, it will be reported as $CDS_AUDIO$.  If it has
907	  both audio and data tracks, it will return $CDS_MIXED$.  If there
908	  are no audio tracks on the disc, and if the CD in question has any
909	  CD-I tracks on it, it will be reported as $CDS_XA_2_2$.  Failing
910	  that, if the CD in question has any XA tracks on it, it will be
911	  reported as $CDS_XA_2_1$.  Finally, if the CD in question has any
912	  data tracks on it, it will be reported as a data CD ($CDS_DATA_1$).
913	
914	  This $ioctl$ can return:
915	  $$
916	  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
917	    CDS_NO_INFO& no information available\cr
918	    CDS_NO_DISC& no disc is inserted, or tray is opened\cr
919	    CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr
920	    CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr
921	    CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr
922	    CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324  user bytes)\cr
923	    CDS_MIXED& mixed audio/data disc\cr
924	    }
925	  $$
926	  For some information concerning frame layout of the various disc
927	  types, see a recent version of \cdromh.
928	
929	\item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a
930	  juke-box. 
931	\item[CDROMRESET] Reset the drive. 
932	\item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the
933	  drive. Refer to section \ref{capability} for more information on
934	  these flags.
935	\item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$
936	  unlocks the door, any other value locks it.
937	\item[CDROM_DEBUG] Turns on debugging info. Only root is allowed
938	  to do this. Same semantics as CDROM_LOCKDOOR.
939	\end{description}
940	
941	\subsubsection{Device dependent $ioctl$s}
942	
943	Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
944	if implemented. No memory allocation or verification is carried out. 
945	
946	\newsection{How to update your driver}
947	
948	\begin{enumerate}
949	\item Make a backup of your current driver. 
950	\item Get hold of the files \cdromc\ and \cdromh, they should be in
951	  the directory tree that came with this documentation.
952	\item Make sure you include \cdromh.
953	\item Change the 3rd argument of $register_blkdev$ from
954	$\&<your-drive>_fops$ to $\&cdrom_fops$. 
955	\item Just after that line, add the following to register with the \UCD:
956	  $$register_cdrom(\&<your-drive>_info);$$
957	  Similarly, add a call to $unregister_cdrom()$ at the appropriate place.
958	\item Copy an example of the device-operations $struct$ to your
959	  source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all
960	  entries to names corresponding to your driver, or names you just
961	  happen to like. If your driver doesn't support a certain function,
962	  make the entry $NULL$. At the entry $capability$ you should list all
963	  capabilities your driver currently supports. If your driver
964	  has a capability that is not listed, please send me a message.
965	\item Copy the $cdrom_device_info$ declaration from the same example
966	  driver, and modify the entries according to your needs. If your
967	  driver dynamically determines the capabilities of the hardware, this
968	  structure should also be declared dynamically. 
969	\item Implement all functions in your $<device>_dops$ structure,
970	  according to prototypes listed in \cdromh, and specifications given
971	  in section~\ref{cdrom.c}. Most likely you have already implemented
972	  the code in a large part, and you will almost certainly need to adapt the
973	  prototype and return values.
974	\item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and
975	  change the prototype a little. Remove entries listed in the first
976	  part in section~\ref{cdrom-ioctl}, if your code was OK, these are
977	  just calls to the routines you adapted in the previous step.
978	\item You may remove all remaining memory checking code in the
979	  $audio_ioctl()$ function that deals with audio commands (these are
980	  listed in the second part of section~\ref{cdrom-ioctl}). There is no
981	  need for memory allocation either, so most $case$s in the $switch$
982	  statement look similar to:
983	  $$
984	  case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\ 
985	  cdrom_tocentry *{})\ arg\bigr);
986	  $$
987	\item All remaining $ioctl$ cases must be moved to a separate
988	  function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that
989	  memory checking and allocation must be kept in this code!
990	\item Change the prototypes of $<device>_open()$ and
991	  $<device>_release()$, and remove any strategic code (\ie, tray
992	  movement, door locking, etc.).
993	\item Try to recompile the drivers. We advise you to use modules, both
994	  for {\tt {cdrom.o}} and your driver, as debugging is much easier this
995	  way.
996	\end{enumerate} 
997	
998	\newsection{Thanks}
999	
1000	Thanks to all the people involved.  First, Erik Andersen, who has
1001	taken over the torch in maintaining \cdromc\ and integrating much
1002	\cdrom-related code in the 2.1-kernel.  Thanks to Scott Snyder and
1003	Gerd Knorr, who were the first to implement this interface for SCSI
1004	and IDE-CD drivers and added many ideas for extension of the data
1005	structures relative to kernel~2.0.  Further thanks to Heiko Ei{\sz}feldt,
1006	Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
1007	Kroll, the \linux\ \cdrom\ device driver developers who were kind
1008	enough to give suggestions and criticisms during the writing. Finally
1009	of course, I want to thank Linus Torvalds for making this possible in
1010	the first place.
1011	
1012	\vfill
1013	$ \version\ $
1014	\eject
1015	\end{document}
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