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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 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	
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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	$$
231	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
232	  $/*$ \rm# $*/$\hfil\cr
233	struct& cdrom_device_ops\ \{ \hidewidth\cr
234	  &int& (* open)(struct\ cdrom_device_info *, int)\cr
235	  &void& (* release)(struct\ cdrom_device_info *);\cr 
236	  &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr     
237	  &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 
238	  &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
239	  &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
240	  &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
241	  &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
242	  &int& (* get_last_session) (struct\ cdrom_device_info *, 
243	        struct\ cdrom_multisession *{});\cr
244	  &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
245	  &int& (* reset)(struct\ cdrom_device_info *);\cr
246	  &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
247	        void *{});\cr 
248	  &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
249	        unsigned\ long);\cr
250	\noalign{\medskip}
251	  &const\ int& capability;& capability flags \cr
252	  &int& n_minors;& number of active minor devices \cr
253	\};\cr
254	}
255	$$
256	When a low-level device driver implements one of these capabilities,
257	it should add a function pointer to this $struct$. When a particular
258	function is not implemented, however, this $struct$ should contain a
259	NULL instead. The $capability$ flags specify the capabilities of the
260	\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
261	is registered with the \UCD. The value $n_minors$ should be a positive
262	value indicating the number of minor devices that are supported by
263	the low-level device driver, normally~1. Although these two variables
264	are `informative' rather than `operational,' they are included in
265	$cdrom_device_ops$ because they describe the capability of the {\em
266	driver\/} rather than the {\em drive}. Nomenclature has always been
267	difficult in computer programming.
268	
269	Note that most functions have fewer parameters than their
270	$blkdev_fops$ counterparts. This is because very little of the
271	information in the structures $inode$ and $file$ is used. For most
272	drivers, the main parameter is the $struct$ $cdrom_device_info$, from
273	which the major and minor number can be extracted. (Most low-level
274	\cdrom\ drivers don't even look at the major and minor number though,
275	since many of them only support one device.) This will be available
276	through $dev$ in $cdrom_device_info$ described below.
277	
278	The drive-specific, minor-like information that is registered with
279	\cdromc, currently contains the following fields:
280	$$
281	\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
282	  $/*$ \rm# $*/$\hfil\cr
283	struct& cdrom_device_info\ \{ \hidewidth\cr
284	  & struct\ cdrom_device_ops *& ops;& device operations for this major\cr
285	  & struct\ cdrom_device_info *& next;& next device_info for this major\cr
286	  & void *&  handle;& driver-dependent data\cr
287	\noalign{\medskip}
288	  & kdev_t&  dev;& device number (incorporates minor)\cr
289	  & int& mask;& mask of capability: disables them \cr
290	  & int& speed;& maximum speed for reading data \cr
291	  & int& capacity;& number of discs in a jukebox \cr
292	\noalign{\medskip}
293	  &int& options : 30;& options flags \cr
294	  &unsigned& mc_flags : 2;& media-change buffer flags \cr
295	  & int& use_count;& number of times device is opened\cr
296	  & char& name[20];& name of the device type\cr
297	\}\cr
298	}$$
299	Using this $struct$, a linked list of the registered minor devices is
300	built, using the $next$ field. The device number, the device operations
301	struct and specifications of properties of the drive are stored in this
302	structure.
303	
304	The $mask$ flags can be used to mask out some of the capabilities listed
305	in $ops\to capability$, if a specific drive doesn't support a feature
306	of the driver. The value $speed$ specifies the maximum head-rate of the
307	drive, measured in units of normal audio speed (176\,kB/sec raw data or
308	150\,kB/sec file system data). The value $n_discs$ should reflect the
309	number of discs the drive can hold simultaneously, if it is designed
310	as a juke-box, or otherwise~1. The parameters are declared $const$
311	because they describe properties of the drive, which don't change after
312	registration.
313	
314	A few registers contain variables local to the \cdrom\ drive. The
315	flags $options$ are used to specify how the general \cdrom\ routines
316	should behave. These various flags registers should provide enough
317	flexibility to adapt to the different users' wishes (and {\em not\/} the
318	`arbitrary' wishes of the author of the low-level device driver, as is
319	the case in the old scheme). The register $mc_flags$ is used to buffer
320	the information from $media_changed()$ to two separate queues. Other
321	data that is specific to a minor drive, can be accessed through $handle$,
322	which can point to a data structure specific to the low-level driver.
323	The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
324	initialized.
325	
326	The intermediate software layer that \cdromc\ forms will perform some
327	additional bookkeeping. The use count of the device (the number of
328	processes that have the device opened) is registered in $use_count$. The
329	function $cdrom_ioctl()$ will verify the appropriate user-memory regions
330	for read and write, and in case a location on the CD is transferred,
331	it will `sanitize' the format by making requests to the low-level
332	drivers in a standard format, and translating all formats between the
333	user-software and low level drivers. This relieves much of the drivers'
334	memory checking and format checking and translation. Also, the necessary
335	structures will be declared on the program stack.
336	
337	The implementation of the functions should be as defined in the
338	following sections. Two functions {\em must\/} be implemented, namely
339	$open()$ and $release()$. Other functions may be omitted, their
340	corresponding capability flags will be cleared upon registration.
341	Generally, a function returns zero on success and negative on error. A
342	function call should return only after the command has completed, but of
343	course waiting for the device should not use processor time.
344	
345	\subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
346	
347	$Open()$ should try to open the device for a specific $purpose$, which
348	can be either:
349	\begin{itemize}
350	\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
351	user commands {\tt {dd}} or {\tt {cat}}.  
352	\item[1] Open for $ioctl$ commands, as done by audio-CD playing
353	programs.
354	\end{itemize}
355	Notice that any strategic code (closing tray upon $open()$, etc.)\ is
356	done by the calling routine in \cdromc, so the low-level routine
357	should only be concerned with proper initialization, such as spinning
358	up the disc, etc. % and device-use count
359	
360	
361	\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
362	
363	
364	Device-specific actions should be taken such as spinning down the device.
365	However, strategic actions such as ejection of the tray, or unlocking
366	the door, should be left over to the general routine $cdrom_release()$.
367	This is the only function returning type $void$.
368	
369	\subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
370	\label{drive status}
371	
372	The function $drive_status$, if implemented, should provide
373	information on the status of the drive (not the status of the disc,
374	which may or may not be in the drive). If the drive is not a changer,
375	$slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 
376	$$
377	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
378	CDS_NO_INFO& no information available\cr
379	CDS_NO_DISC& no disc is inserted, tray is closed\cr
380	CDS_TRAY_OPEN& tray is opened\cr
381	CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
382	CDS_DISC_OK& a disc is loaded and everything is fine\cr
383	}
384	$$
385	
386	\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
387	
388	This function is very similar to the original function in $struct\ 
389	file_operations$. It returns 1 if the medium of the device $cdi\to
390	dev$ has changed since the last call, and 0 otherwise. The parameter
391	$disc_nr$ identifies a specific slot in a juke-box, it should be
392	ignored for single-disc drives.  Note that by `re-routing' this
393	function through $cdrom_media_changed()$, we can implement separate
394	queues for the VFS and a new $ioctl()$ function that can report device
395	changes to software (\eg, an auto-mounting daemon).
396	
397	\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
398	
399	This function, if implemented, should control the tray movement. (No
400	other function should control this.) The parameter $position$ controls
401	the desired direction of movement:
402	\begin{itemize}
403	\item[0] Close tray
404	\item[1] Open tray
405	\end{itemize}
406	This function returns 0 upon success, and a non-zero value upon
407	error. Note that if the tray is already in the desired position, no
408	action need be taken, and the return value should be 0. 
409	
410	\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
411	
412	This function (and no other code) controls locking of the door, if the
413	drive allows this. The value of $lock$ controls the desired locking
414	state:
415	\begin{itemize}
416	\item[0] Unlock door, manual opening is allowed
417	\item[1] Lock door, tray cannot be ejected manually
418	\end{itemize}
419	This function returns 0 upon success, and a non-zero value upon
420	error. Note that if the door is already in the requested state, no
421	action need be taken, and the return value should be 0. 
422	
423	\subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
424	
425	Some \cdrom\ drives are capable of changing their head-speed. There
426	are several reasons for changing the speed of a \cdrom\ drive. Badly
427	pressed \cdrom s may benefit from less-than-maximum head rate. Modern
428	\cdrom\ drives can obtain very high head rates (up to $24\times$ is
429	common).  It has been reported that these drives can make reading
430	errors at these high speeds, reducing the speed can prevent data loss
431	in these circumstances.  Finally, some of these drives can
432	make an annoyingly loud noise, which a lower speed may reduce. %Finally,
433	%although the audio-low-pass filters probably aren't designed for it,
434	%more than real-time playback of audio might be used for high-speed
435	%copying of audio tracks.
436	
437	This function specifies the speed at which data is read or audio is
438	played back. The value of $speed$ specifies the head-speed of the
439	drive, measured in units of standard cdrom speed (176\,kB/sec raw data
440	or 150\,kB/sec file system data). So to request that a \cdrom\ drive
441	operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
442	with $speed=2$. The special value `0' means `auto-selection', \ie,
443	maximum data-rate or real-time audio rate. If the drive doesn't have
444	this `auto-selection' capability, the decision should be made on the
445	current disc loaded and the return value should be positive. A negative
446	return value indicates an error.
447	
448	\subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
449	
450	If the drive can store multiple discs (a juke-box) this function
451	will perform disc selection. It should return the number of the
452	selected disc on success, a negative value on error. Currently, only
453	the ide-cd driver supports this functionality.
454	
455	\subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\
456	  cdrom_multisession * ms_info)$}
457	
458	This function should implement the old corresponding $ioctl()$. For
459	device $cdi\to dev$, the start of the last session of the current disc
460	should be returned in the pointer argument $ms_info$. Note that
461	routines in \cdromc\ have sanitized this argument: its requested
462	format will {\em always\/} be of the type $CDROM_LBA$ (linear block
463	addressing mode), whatever the calling software requested. But
464	sanitization goes even further: the low-level implementation may
465	return the requested information in $CDROM_MSF$ format if it wishes so
466	(setting the $ms_info\rightarrow addr_format$ field appropriately, of
467	course) and the routines in \cdromc\ will make the transformation if
468	necessary. The return value is 0 upon success.
469	
470	\subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
471	  cdrom_mcn * mcn)$}
472	
473	Some discs carry a `Media Catalog Number' (MCN), also called
474	`Universal Product Code' (UPC). This number should reflect the number
475	that is generally found in the bar-code on the product. Unfortunately,
476	the few discs that carry such a number on the disc don't even use the
477	same format. The return argument to this function is a pointer to a
478	pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
479	expected as a 13-character string, terminated by a null-character.
480	
481	\subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
482	
483	This call should perform a hard-reset on the drive (although in
484	circumstances that a hard-reset is necessary, a drive may very well not
485	listen to commands anymore). Preferably, control is returned to the
486	caller only after the drive has finished resetting. If the drive is no
487	longer listening, it may be wise for the underlying low-level cdrom
488	driver to time out.
489	
490	\subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
491	  int\ cmd, void * arg)$}
492	
493	Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
494	implemented by the routines described above, and hence the function
495	$cdrom_ioctl$ will use those. However, most $ioctl$s deal with
496	audio-control. We have decided to leave these to be accessed through a
497	single function, repeating the arguments $cmd$ and $arg$. Note that
498	the latter is of type $void*{}$, rather than $unsigned\ long\
499	int$. The routine $cdrom_ioctl()$ does do some useful things,
500	though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
501	Seconds, Frames) for all audio calls. It also verifies the memory
502	location of $arg$, and reserves stack-memory for the argument. This
503	makes implementation of the $audio_ioctl()$ much simpler than in the
504	old driver scheme. For example, you may look up the function
505	$cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
506	this documentation. 
507	
508	An unimplemented ioctl should return $-ENOSYS$, but a harmless request
509	(\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
510	errors should be according to the standards, whatever they are. When
511	an error is returned by the low-level driver, the \UCD\ tries whenever
512	possible to return the error code to the calling program. (We may decide
513	to sanitize the return value in $cdrom_ioctl()$ though, in order to
514	guarantee a uniform interface to the audio-player software.)
515	
516	\subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\
517	  cmd, unsigned\ long\ arg)$}
518	
519	Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
520	they are introduced to service some capabilities of certain drives. In
521	fact, there are 6 different $ioctl$s for reading data, either in some
522	particular kind of format, or audio data. Not many drives support
523	reading audio tracks as data, I believe this is because of protection
524	of copyrights of artists. Moreover, I think that if audio-tracks are
525	supported, it should be done through the VFS and not via $ioctl$s. A
526	problem here could be the fact that audio-frames are 2352 bytes long,
527	so either the audio-file-system should ask for 75264 bytes at once
528	(the least common multiple of 512 and 2352), or the drivers should
529	bend their backs to cope with this incoherence (to which I would be
530	opposed).  Furthermore, it is very difficult for the hardware to find
531	the exact frame boundaries, since there are no synchronization headers
532	in audio frames.  Once these issues are resolved, this code should be
533	standardized in \cdromc.
534	
535	Because there are so many $ioctl$s that seem to be introduced to
536	satisfy certain drivers,\footnote{Is there software around that
537	  actually uses these? I'd be interested!} any `non-standard' $ioctl$s
538	are routed through the call $dev_ioctl()$. In principle, `private'
539	$ioctl$s should be numbered after the device's major number, and not
540	the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
541	non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2,
542	  CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK,
543	  CDROMPLAY\-BLK and CDROM\-READALL}.
544	
545	
546	\subsection{\cdrom\ capabilities}
547	\label{capability}
548	
549	Instead of just implementing some $ioctl$ calls, the interface in
550	\cdromc\ supplies the possibility to indicate the {\em capabilities\/}
551	of a \cdrom\ drive. This can be done by ORing any number of
552	capability-constants that are defined in \cdromh\ at the registration
553	phase. Currently, the capabilities are any of:
554	$$
555	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
556	CDC_CLOSE_TRAY& can close tray by software control\cr
557	CDC_OPEN_TRAY& can open tray\cr
558	CDC_LOCK& can lock and unlock the door\cr
559	CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
560	CDC_SELECT_DISC& drive is juke-box\cr
561	CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
562	CDC_MCN& can read Media Catalog Number\cr
563	CDC_MEDIA_CHANGED& can report if disc has changed\cr
564	CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
565	CDC_RESET& hard reset device\cr
566	CDC_IOCTLS& driver has non-standard ioctls\cr
567	CDC_DRIVE_STATUS& driver implements drive status\cr
568	}
569	$$
570	The capability flag is declared $const$, to prevent drivers from
571	accidentally tampering with the contents. The capability fags actually
572	inform \cdromc\ of what the driver can do. If the drive found
573	by the driver does not have the capability, is can be masked out by
574	the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
575	driver has implemented the code for loading and ejecting \cdrom's, and
576	hence its corresponding flags in $capability$ will be set. But a SCSI
577	\cdrom\ drive might be a caddy system, which can't load the tray, and
578	hence for this drive the $cdrom_device_info$ struct will have set
579	the $CDC_CLOSE_TRAY$ bit in $mask$.
580	
581	In the file \cdromc\ you will encounter many constructions of the type
582	$$\it
583	if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 
584	   \mathrel{\&} CDC_<capability>) \ldots
585	$$
586	There is no $ioctl$ to set the mask\dots The reason is that
587	I think it is better to control the {\em behavior\/} rather than the
588	{\em capabilities}.
589	
590	\subsection{Options}
591	
592	A final flag register controls the {\em behavior\/} of the \cdrom\
593	drives, in order to satisfy different users' wishes, hopefully
594	independently of the ideas of the respective author who happened to
595	have made the drive's support available to the \linux\ community. The
596	current behavior options are:
597	$$
598	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
599	CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
600	CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
601	CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
602	 purpose for $open()$\cr
603	CDO_LOCK& try to lock door if device is opened\cr
604	CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
605	}
606	$$
607	
608	The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
609	CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
610	interface and software standards. Before you protest, there are two
611	new $ioctl$s implemented in \cdromc, that allow you to control the
612	behavior by software. These are:
613	$$
614	\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
615	CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
616	CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
617	}
618	$$
619	One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
620	newsection we explain what the need for this option is.
621	
622	A software package {\tt setcd}, available from the Debian distribution
623	and {\tt sunsite.unc.edu}, allows user level control of these flags. 
624	
625	\newsection{The need to know the purpose of opening the \cdrom\ device}
626	
627	Traditionally, Unix devices can be used in two different `modes',
628	either by reading/writing to the device file, or by issuing
629	controlling commands to the device, by the device's $ioctl()$
630	call. The problem with \cdrom\ drives, is that they can be used for
631	two entirely different purposes. One is to mount removable
632	file systems, \cdrom s, the other is to play audio CD's. Audio commands
633	are implemented entirely through $ioctl$s, presumably because the
634	first implementation (SUN?) has been such. In principle there is
635	nothing wrong with this, but a good control of the `CD player' demands
636	that the device can {\em always\/} be opened in order to give the
637	$ioctl$ commands, regardless of the state the drive is in. 
638	
639	On the other hand, when used as a removable-media disc drive (what the
640	original purpose of \cdrom s is) we would like to make sure that the
641	disc drive is ready for operation upon opening the device. In the old
642	scheme, some \cdrom\ drivers don't do any integrity checking, resulting
643	in a number of i/o errors reported by the VFS to the kernel when an
644	attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
645	particularly elegant way to find out that there is no \cdrom\ inserted;
646	it more-or-less looks like the old IBM-PC trying to read an empty floppy
647	drive for a couple of seconds, after which the system complains it
648	can't read from it. Nowadays we can {\em sense\/} the existence of a
649	removable medium in a drive, and we believe we should exploit that
650	fact. An integrity check on opening of the device, that verifies the
651	availability of a \cdrom\ and its correct type (data), would be
652	desirable.
653	
654	These two ways of using a \cdrom\ drive, principally for data and
655	secondarily for playing audio discs, have different demands for the
656	behavior of the $open()$ call. Audio use simply wants to open the
657	device in order to get a file handle which is needed for issuing
658	$ioctl$ commands, while data use wants to open for correct and
659	reliable data transfer. The only way user programs can indicate what
660	their {\em purpose\/} of opening the device is, is through the $flags$
661	parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
662	implemented (some drivers implement checking for write-related flags,
663	but this is not strictly necessary if the device file has correct
664	permission flags). Most option flags simply don't make sense to
665	\cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and
666	$O_SYNC$ have no meaning to a \cdrom. 
667	
668	We therefore propose to use the flag $O_NONBLOCK$ to indicate
669	that the device is opened just for issuing $ioctl$
670	commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
671	subsequent calls to the device don't cause the calling process to
672	wait. We could interpret this as ``don't wait until someone has
673	inserted some valid data-\cdrom.'' Thus, our proposal of the
674	implementation for the $open()$ call for \cdrom s is:
675	\begin{itemize}
676	\item If no other flags are set than $O_RDONLY$, the device is opened
677	for data transfer, and the return value will be 0 only upon successful
678	initialization of the transfer. The call may even induce some actions
679	on the \cdrom, such as closing the tray.  
680	\item If the option flag $O_NONBLOCK$ is set, opening will always be
681	successful, unless the whole device doesn't exist. The drive will take
682	no actions whatsoever. 
683	\end{itemize}
684	
685	\subsection{And what about standards?}
686	
687	You might hesitate to accept this proposal as it comes from the
688	\linux\ community, and not from some standardizing institute. What
689	about SUN, SGI, HP and all those other Unix and hardware vendors?
690	Well, these companies are in the lucky position that they generally
691	control both the hardware and software of their supported products,
692	and are large enough to set their own standard. They do not have to
693	deal with a dozen or more different, competing hardware
694	configurations.\footnote{Incidentally, I think that SUN's approach to
695	mounting \cdrom s is very good in origin: under Solaris a
696	volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
697	{/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
698	further and have {\em every\/} \cdrom\ on the local area network be
699	mounted at the similar location, \ie, no matter in which particular
700	machine you insert a \cdrom, it will always appear at the same
701	position in the directory tree, on every system. When I wanted to
702	implement such a user-program for \linux, I came across the
703	differences in behavior of the various drivers, and the need for an
704	$ioctl$ informing about media changes.}
705	
706	We believe that using $O_NONBLOCK$ to indicate that a device is being opened
707	for $ioctl$ commands only can be easily introduced in the \linux\
708	community. All the CD-player authors will have to be informed, we can
709	even send in our own patches to the programs. The use of $O_NONBLOCK$
710	has most likely no influence on the behavior of the CD-players on
711	other operating systems than \linux. Finally, a user can always revert
712	to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
713	CDO_USE_FFLAGS)$. 
714	
715	\subsection{The preferred strategy of $open()$}
716	
717	The routines in \cdromc\ are designed in such a way that run-time
718	configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
719	can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
720	modes of operation can be set:
721	\begin{description}
722	\item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
723	is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
724	future.) If the device is not yet opened by any other process, and if
725	the device is being opened for data ($O_NONBLOCK$ is not set) and the
726	tray is found to be open, an attempt to close the tray is made. Then,
727	it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
728	set, that it contains tracks of type `data mode 1.' Only if all tests
729	are passed is the return value zero. The door is locked to prevent file
730	system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
731	set), no actions are taken and a value of 0 will be returned. 
732	\item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This
733	mimics the behavior of the current sbpcd-driver. The option flags are
734	ignored, the tray is closed on the first open, if necessary. Similarly,
735	the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
736	it is automatically ejected, such that the user can replace it.
737	\end{description} 
738	We hope that these option can convince everybody (both driver
739	maintainers and user program developers) to adopt the new \cdrom\
740	driver scheme and option flag interpretation.
741	
742	\newsection{Description of routines in \cdromc}
743	
744	Only a few routines in \cdromc\ are exported to the drivers. In this
745	new section we will discuss these, as well as the functions that `take
746	over' the \cdrom\ interface to the kernel. The header file belonging
747	to \cdromc\ is called \cdromh. Formerly, some of the contents of this
748	file were placed in the file {\tt {ucdrom.h}}, but this file has now been
749	merged back into \cdromh.
750	
751	\subsection{$Struct\ file_operations\ cdrom_fops$}
752	
753	The contents of this structure were described in section~\ref{cdrom.c}.
754	A pointer to this structure is assigned to the $fops$ field
755	of the $struct gendisk$.
756	
757	\subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
758	
759	This function is used in about the same way one registers $cdrom_fops$
760	with the kernel, the device operations and information structures,
761	as described in section~\ref{cdrom.c}, should be registered with the
762	\UCD:
763	$$
764	register_cdrom(\&<device>_info));
765	$$
766	This function returns zero upon success, and non-zero upon
767	failure. The structure $<device>_info$ should have a pointer to the
768	driver's $<device>_dops$, as in 
769	$$
770	\vbox{\halign{&$#$\hfil\cr
771	struct\ &cdrom_device_info\ <device>_info = \{\cr
772	& <device>_dops;\cr
773	&\ldots\cr
774	\}\cr
775	}}$$
776	Note that a driver must have one static structure, $<device>_dops$, while
777	it may have as many structures $<device>_info$ as there are minor devices
778	active. $Register_cdrom()$ builds a linked list from these. 
779	
780	\subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
781	
782	Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
783	the minor device from the list. If it was the last registered minor for
784	the low-level driver, this disconnects the registered device-operation
785	routines from the \cdrom\ interface. This function returns zero upon
786	success, and non-zero upon failure.
787	
788	\subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
789	
790	This function is not called directly by the low-level drivers, it is
791	listed in the standard $cdrom_fops$. If the VFS opens a file, this
792	function becomes active. A strategy is implemented in this routine,
793	taking care of all capabilities and options that are set in the
794	$cdrom_device_ops$ connected to the device. Then, the program flow is
795	transferred to the device_dependent $open()$ call.
796	
797	\subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
798	*fp)$}
799	
800	This function implements the reverse-logic of $cdrom_open()$, and then
801	calls the device-dependent $release()$ routine. When the use-count has
802	reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
803	and $invalidate_buffers(dev)$.
804	
805	
806	\subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
807	unsigned\ int\ cmd, unsigned\ long\ arg)$}
808	\label{cdrom-ioctl}
809	
810	This function handles all the standard $ioctl$ requests for \cdrom\
811	devices in a uniform way. The different calls fall into three
812	categories: $ioctl$s that can be directly implemented by device
813	operations, ones that are routed through the call $audio_ioctl()$, and
814	the remaining ones, that are presumable device-dependent. Generally, a
815	negative return value indicates an error.
816	
817	\subsubsection{Directly implemented $ioctl$s}
818	\label{ioctl-direct}
819	
820	The following `old' \cdrom-$ioctl$s are implemented by directly
821	calling device-operations in $cdrom_device_ops$, if implemented and
822	not masked:
823	\begin{description}
824	\item[CDROMMULTISESSION] Requests the last session on a \cdrom.
825	\item[CDROMEJECT] Open tray. 
826	\item[CDROMCLOSETRAY] Close tray.
827	\item[CDROMEJECT_SW] If $arg\not=0$, set behavior to auto-close (close
828	tray on first open) and auto-eject (eject on last release), otherwise
829	set behavior to non-moving on $open()$ and $release()$ calls.
830	\item[CDROM_GET_MCN] Get the Media Catalog Number from a CD.
831	\end{description}
832	
833	\subsubsection{$Ioctl$s routed through $audio_ioctl()$}
834	\label{ioctl-audio}
835	
836	The following set of $ioctl$s are all implemented through a call to
837	the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
838	allocation are performed in $cdrom_ioctl()$, and also sanitization of
839	address format ($CDROM_LBA$/$CDROM_MSF$) is done.
840	\begin{description}
841	\item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
842	cdrom_subchnl *{}$.
843	\item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type
844	$struct\ cdrom_tochdr *{}$. 
845	\item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and
846	specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
847	\item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
848	Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
849	\item[CDROMPLAYTRKIND] Play audio fragment in track-index format
850	delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
851	\item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
852	cdrom_volctrl *{}$.
853	\item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
854	cdrom_volctrl *{}$.
855	\item[CDROMSTART] Spin up disc.
856	\item[CDROMSTOP] Stop playback of audio fragment.
857	\item[CDROMPAUSE] Pause playback of audio fragment.
858	\item[CDROMRESUME] Resume playing.
859	\end{description}
860	
861	\subsubsection{New $ioctl$s in \cdromc}
862	
863	The following $ioctl$s have been introduced to allow user programs to
864	control the behavior of individual \cdrom\ devices. New $ioctl$
865	commands can be identified by the underscores in their names.
866	\begin{description}
867	\item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
868	option flag register after modification. Use  $arg = \rm0$ for reading
869	the current flags.
870	\item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns
871	  the option flag register after modification.
872	\item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as
873	  by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or
874	  150\,kB/sec file system data). The value 0 means `auto-select', \ie,
875	  play audio discs at real time and data discs at maximum speed. The value
876	  $arg$ is checked against the maximum head rate of the drive found in the
877	  $cdrom_dops$.
878	\item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box.
879	  First disc is numbered 0. The number $arg$ is checked against the
880	  maximum number of discs in the juke-box found in the $cdrom_dops$.
881	\item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since
882	  the last call. Note that calls to $cdrom_media_changed$ by the VFS
883	  are treated by an independent queue, so both mechanisms will detect
884	  a media change once. For juke-boxes, an extra argument $arg$
885	  specifies the slot for which the information is given. The special
886	  value $CDSL_CURRENT$ requests that information about the currently
887	  selected slot be returned.
888	\item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to
889	  $drive_status()$. Return values are defined in section~\ref{drive
890	   status}. Note that this call doesn't return information on the
891	  current playing activity of the drive; this can be polled through an
892	  $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument
893	  $arg$ specifies the slot for which (possibly limited) information is
894	  given. The special value $CDSL_CURRENT$ requests that information
895	  about the currently selected slot be returned.
896	\item[CDROM_DISC_STATUS] Returns the type of the disc currently in the
897	  drive.  It should be viewed as a complement to $CDROM_DRIVE_STATUS$.
898	  This $ioctl$ can provide \emph {some} information about the current
899	  disc that is inserted in the drive.  This functionality used to be
900	  implemented in the low level drivers, but is now carried out
901	  entirely in \UCD.
902	  
903	  The history of development of the CD's use as a carrier medium for
904	  various digital information has lead to many different disc types.
905	  This $ioctl$ is useful only in the case that CDs have \emph {only
906	    one} type of data on them.  While this is often the case, it is
907	  also very common for CDs to have some tracks with data, and some
908	  tracks with audio.  Because this is an existing interface, rather
909	  than fixing this interface by changing the assumptions it was made
910	  under, thereby breaking all user applications that use this
911	  function, the \UCD\ implements this $ioctl$ as follows: If the CD in
912	  question has audio tracks on it, and it has absolutely no CD-I, XA,
913	  or data tracks on it, it will be reported as $CDS_AUDIO$.  If it has
914	  both audio and data tracks, it will return $CDS_MIXED$.  If there
915	  are no audio tracks on the disc, and if the CD in question has any
916	  CD-I tracks on it, it will be reported as $CDS_XA_2_2$.  Failing
917	  that, if the CD in question has any XA tracks on it, it will be
918	  reported as $CDS_XA_2_1$.  Finally, if the CD in question has any
919	  data tracks on it, it will be reported as a data CD ($CDS_DATA_1$).
920	
921	  This $ioctl$ can return:
922	  $$
923	  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
924	    CDS_NO_INFO& no information available\cr
925	    CDS_NO_DISC& no disc is inserted, or tray is opened\cr
926	    CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr
927	    CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr
928	    CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr
929	    CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324  user bytes)\cr
930	    CDS_MIXED& mixed audio/data disc\cr
931	    }
932	  $$
933	  For some information concerning frame layout of the various disc
934	  types, see a recent version of \cdromh.
935	
936	\item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a
937	  juke-box. 
938	\item[CDROMRESET] Reset the drive. 
939	\item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the
940	  drive. Refer to section \ref{capability} for more information on
941	  these flags.
942	\item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$
943	  unlocks the door, any other value locks it.
944	\item[CDROM_DEBUG] Turns on debugging info. Only root is allowed
945	  to do this. Same semantics as CDROM_LOCKDOOR.
946	\end{description}
947	
948	\subsubsection{Device dependent $ioctl$s}
949	
950	Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
951	if implemented. No memory allocation or verification is carried out. 
952	
953	\newsection{How to update your driver}
954	
955	\begin{enumerate}
956	\item Make a backup of your current driver. 
957	\item Get hold of the files \cdromc\ and \cdromh, they should be in
958	  the directory tree that came with this documentation.
959	\item Make sure you include \cdromh.
960	\item Change the 3rd argument of $register_blkdev$ from
961	$\&<your-drive>_fops$ to $\&cdrom_fops$. 
962	\item Just after that line, add the following to register with the \UCD:
963	  $$register_cdrom(\&<your-drive>_info);$$
964	  Similarly, add a call to $unregister_cdrom()$ at the appropriate place.
965	\item Copy an example of the device-operations $struct$ to your
966	  source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all
967	  entries to names corresponding to your driver, or names you just
968	  happen to like. If your driver doesn't support a certain function,
969	  make the entry $NULL$. At the entry $capability$ you should list all
970	  capabilities your driver currently supports. If your driver
971	  has a capability that is not listed, please send me a message.
972	\item Copy the $cdrom_device_info$ declaration from the same example
973	  driver, and modify the entries according to your needs. If your
974	  driver dynamically determines the capabilities of the hardware, this
975	  structure should also be declared dynamically. 
976	\item Implement all functions in your $<device>_dops$ structure,
977	  according to prototypes listed in \cdromh, and specifications given
978	  in section~\ref{cdrom.c}. Most likely you have already implemented
979	  the code in a large part, and you will almost certainly need to adapt the
980	  prototype and return values.
981	\item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and
982	  change the prototype a little. Remove entries listed in the first
983	  part in section~\ref{cdrom-ioctl}, if your code was OK, these are
984	  just calls to the routines you adapted in the previous step.
985	\item You may remove all remaining memory checking code in the
986	  $audio_ioctl()$ function that deals with audio commands (these are
987	  listed in the second part of section~\ref{cdrom-ioctl}). There is no
988	  need for memory allocation either, so most $case$s in the $switch$
989	  statement look similar to:
990	  $$
991	  case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\ 
992	  cdrom_tocentry *{})\ arg\bigr);
993	  $$
994	\item All remaining $ioctl$ cases must be moved to a separate
995	  function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that
996	  memory checking and allocation must be kept in this code!
997	\item Change the prototypes of $<device>_open()$ and
998	  $<device>_release()$, and remove any strategic code (\ie, tray
999	  movement, door locking, etc.).
1000	\item Try to recompile the drivers. We advise you to use modules, both
1001	  for {\tt {cdrom.o}} and your driver, as debugging is much easier this
1002	  way.
1003	\end{enumerate} 
1004	
1005	\newsection{Thanks}
1006	
1007	Thanks to all the people involved.  First, Erik Andersen, who has
1008	taken over the torch in maintaining \cdromc\ and integrating much
1009	\cdrom-related code in the 2.1-kernel.  Thanks to Scott Snyder and
1010	Gerd Knorr, who were the first to implement this interface for SCSI
1011	and IDE-CD drivers and added many ideas for extension of the data
1012	structures relative to kernel~2.0.  Further thanks to Heiko Ei{\sz}feldt,
1013	Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
1014	Kroll, the \linux\ \cdrom\ device driver developers who were kind
1015	enough to give suggestions and criticisms during the writing. Finally
1016	of course, I want to thank Linus Torvalds for making this possible in
1017	the first place.
1018	
1019	\vfill
1020	$ \version\ $
1021	\eject
1022	\end{document}
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