linux/Documentation/cdrom/cdrom-standard.tex
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  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.}}
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  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
  35the widest variety of hardware devices. The reasons for this are
  36presumably 
  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}
  47The openness of \linux, and the many different types of available
  48hardware has allowed \linux\ to support many different hardware devices.
  49Unfortunately, the very openness that has allowed \linux\ to support
  50all these different devices has also allowed the behavior of each
  51device driver to differ significantly from one device to another.
  52This divergence of behavior has been very significant for \cdrom\
  53devices; the way a particular drive reacts to a `standard' $ioctl()$
  54call varies greatly from one device driver to another. To avoid making
  55their drivers totally inconsistent, the writers of \linux\ \cdrom\
  56drivers generally created new device drivers by understanding, copying,
  57and then changing an existing one. Unfortunately, this practice did not
  58maintain uniform behavior across all the \linux\ \cdrom\ drivers. 
  59
  60This document describes an effort to establish Uniform behavior across
  61all the different \cdrom\ device drivers for \linux. This document also
  62defines the various $ioctl$s, and how the low-level \cdrom\ device
  63drivers should implement them. Currently (as of the \linux\ 2.1.$x$
  64development kernels) several low-level \cdrom\ device drivers, including
  65both IDE/ATAPI and SCSI, now use this Uniform interface.
  66
  67When the \cdrom\ was developed, the interface between the \cdrom\ drive
  68and the computer was not specified in the standards. As a result, many
  69different \cdrom\ interfaces were developed. Some of them had their
  70own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
  71manufacturers adopted an existing electrical interface and changed
  72the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
  73adapted their drives to one or more of the already existing electrical
  74interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
  75most of the `NoName' manufacturers). In cases where a new drive really
  76brought its own interface or used its own command set and flow control
  77scheme, either a separate driver had to be written, or an existing
  78driver had to be enhanced. History has delivered us \cdrom\ support for
  79many of these different interfaces. Nowadays, almost all new \cdrom\
  80drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
  81manufacturer will create a new interface. Even finding drives for the
  82old proprietary interfaces is getting difficult.
  83
  84When (in the 1.3.70's) I looked at the existing software interface,
  85which was expressed through \cdromh, it appeared to be a rather wild
  86set of commands and data formats.\footnote{I cannot recollect what
  87kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
  88latest kernel that I was indirectly involved in.} It seemed that many
  89features of the software interface had been added to accommodate the
  90capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
  91importantly, it appeared that the behavior of the `standard' commands
  92was different for most of the different drivers: \eg, some drivers
  93close the tray if an $open()$ call occurs when the tray is open, while
  94others do not. Some drivers lock the door upon opening the device, to
  95prevent an incoherent file system, but others don't, to allow software
  96ejection. Undoubtedly, the capabilities of the different drives vary,
  97but even when two drives have the same capability their drivers'
  98behavior was usually different.
  99
 100I decided to start a discussion on how to make all the \linux\ \cdrom\
 101drivers behave more uniformly. I began by contacting the developers of
 102the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
 103encouraged me to write the \UCD\ which this document is intended to
 104describe. The implementation of the \UCD\ is in the file \cdromc. This
 105driver is intended to be an additional software layer that sits on top
 106of the low-level device drivers for each \cdrom\ drive. By adding this
 107additional layer, it is possible to have all the different \cdrom\
 108devices behave {\em exactly\/} the same (insofar as the underlying
 109hardware will allow).
 110
 111The goal of the \UCD\ is {\em not\/} to alienate driver developers who
 112have not yet taken steps to support this effort. The goal of \UCD\ is
 113simply 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
 116between the low-level device driver code and the \linux\ kernel. Care
 117is taken that 100\,\% compatibility exists with the data structures and
 118programmer's interface defined in \cdromh. This guide was written to
 119help \cdrom\ driver developers adapt their code to use the \UCD\ code
 120defined in \cdromc.
 121
 122Personally, I think that the most important hardware interfaces are
 123the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
 124of hardware drop continuously, it is also likely that people may have
 125more than one \cdrom\ drive, possibly of mixed types. It is important
 126that these drives behave in the same way. In December 1994, one of the
 127cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
 128drive. In the months that I was busy writing a \linux\ driver for it,
 129proprietary drives became obsolete and IDE/ATAPI drives became the
 130standard. At the time of the last update to this document (November
 1311997) it is becoming difficult to even {\em find} anything less than a
 13216 speed \cdrom\ drive, and 24 speed drives are common.
 133
 134\newsection{Standardizing through another software level}
 135\label{cdrom.c}
 136
 137At the time this document was conceived, all drivers directly
 138implemented the \cdrom\ $ioctl()$ calls through their own routines. This
 139led to the danger of different drivers forgetting to do important things
 140like checking that the user was giving the driver valid data. More
 141importantly, this led to the divergence of behavior, which has already
 142been discussed.
 143
 144For this reason, the \UCD\ was created to enforce consistent \cdrom\
 145drive behavior, and to provide a common set of services to the various
 146low-level \cdrom\ device drivers. The \UCD\ now provides another
 147software-level, that separates the $ioctl()$ and $open()$ implementation
 148from the actual hardware implementation. Note that this effort has
 149made few changes which will affect a user's application programs. The
 150greatest change involved moving the contents of the various low-level
 151\cdrom\ drivers' header files to the kernel's cdrom directory. This was
 152done to help ensure that the user is only presented with only one cdrom
 153interface, the interface defined in \cdromh.
 154
 155\cdrom\ drives are specific enough (\ie, different from other
 156block-devices such as floppy or hard disc drives), to define a set
 157of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
 158These operations are different from the classical block-device file
 159operations, $<block-device>_fops$.
 160
 161The 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
 163device by registering the following general $struct\ file_operations$:
 164$$
 165\halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
 166struct& file_operations\ cdrom_fops = \{\hidewidth\cr
 167        &NULL,                  & lseek \cr
 168        &block_read,            & read---general block-dev read \cr
 169        &block_write,           & write---general block-dev write \cr
 170        &NULL,                  & readdir \cr
 171        &NULL,                  & select \cr
 172        &cdrom_ioctl,           & ioctl \cr
 173        &NULL,                  & mmap \cr
 174        &cdrom_open,            & open \cr
 175        &cdrom_release,         & release \cr
 176        &NULL,                  & fsync \cr
 177        &NULL,                  & fasync \cr
 178        &cdrom_media_changed,   & media change \cr
 179        &NULL                   & revalidate \cr
 180\};\cr
 181}
 182$$ 
 183
 184Every active \cdrom\ device shares this $struct$. The routines
 185declared above are all implemented in \cdromc, since this file is the
 186place where the behavior of all \cdrom-devices is defined and
 187standardized. The actual interface to the various types of \cdrom\ 
 188hardware is still performed by various low-level \cdrom-device
 189drivers. These routines simply implement certain {\em capabilities\/}
 190that are common to all \cdrom\ (and really, all removable-media
 191devices).
 192
 193Registration of a low-level \cdrom\ device driver is now done through
 194the general routines in \cdromc, not through the Virtual File System
 195(VFS) any more. The interface implemented in \cdromc\ is carried out
 196through two general structures that contain information about the
 197capabilities of the driver, and the specific drives on which the
 198driver 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
 211Registering a particular \cdrom\ drive with the \UCD\ is done by the
 212low-level device driver though a call to:
 213$$register_cdrom(struct\ cdrom_device_info * <device>_info)  
 214$$
 215The device information structure, $<device>_info$, contains all the
 216information needed for the kernel to interface with the low-level
 217\cdrom\ device driver. One of the most important entries in this
 218structure is a pointer to the $cdrom_device_ops$ structure of the
 219low-level driver.
 220
 221The device operations structure, $cdrom_device_ops$, contains a list
 222of pointers to the functions which are implemented in the low-level
 223device driver. When \cdromc\ accesses a \cdrom\ device, it does it
 224through the functions in this structure. It is impossible to know all
 225the capabilities of future \cdrom\ drives, so it is expected that this
 226list may need to be expanded from time to time as new technologies are
 227developed. For example, CD-R and CD-R/W drives are beginning to become
 228popular, and support will soon need to be added for them. For now, the
 229current $struct$ is:
 230$$
 231\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
 232  $/*$ \rm# $*/$\hfil\cr
 233struct& cdrom_device_ops\ \{ \hidewidth\cr
 234  &int& (* open)(struct\ cdrom_device_info *, int)\cr
 235  &void& (* release)(struct\ cdrom_device_info *);\cr 
 236  &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr     
 237  &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 
 238  &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
 239  &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
 240  &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
 241  &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
 242  &int& (* get_last_session) (struct\ cdrom_device_info *, 
 243        struct\ cdrom_multisession *{});\cr
 244  &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
 245  &int& (* reset)(struct\ cdrom_device_info *);\cr
 246  &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
 247        void *{});\cr 
 248  &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
 249        unsigned\ long);\cr
 250\noalign{\medskip}
 251  &const\ int& capability;& capability flags \cr
 252  &int& n_minors;& number of active minor devices \cr
 253\};\cr
 254}
 255$$
 256When a low-level device driver implements one of these capabilities,
 257it should add a function pointer to this $struct$. When a particular
 258function is not implemented, however, this $struct$ should contain a
 259NULL instead. The $capability$ flags specify the capabilities of the
 260\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
 261is registered with the \UCD. The value $n_minors$ should be a positive
 262value indicating the number of minor devices that are supported by
 263the low-level device driver, normally~1. Although these two variables
 264are `informative' rather than `operational,' they are included in
 265$cdrom_device_ops$ because they describe the capability of the {\em
 266driver\/} rather than the {\em drive}. Nomenclature has always been
 267difficult in computer programming.
 268
 269Note that most functions have fewer parameters than their
 270$blkdev_fops$ counterparts. This is because very little of the
 271information in the structures $inode$ and $file$ is used. For most
 272drivers, the main parameter is the $struct$ $cdrom_device_info$, from
 273which 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,
 275since many of them only support one device.) This will be available
 276through $dev$ in $cdrom_device_info$ described below.
 277
 278The drive-specific, minor-like information that is registered with
 279\cdromc, currently contains the following fields:
 280$$
 281\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
 282  $/*$ \rm# $*/$\hfil\cr
 283struct& cdrom_device_info\ \{ \hidewidth\cr
 284  & struct\ cdrom_device_ops *& ops;& device operations for this major\cr
 285  & struct\ cdrom_device_info *& next;& next device_info for this major\cr
 286  & void *&  handle;& driver-dependent data\cr
 287\noalign{\medskip}
 288  & kdev_t&  dev;& device number (incorporates minor)\cr
 289  & int& mask;& mask of capability: disables them \cr
 290  & int& speed;& maximum speed for reading data \cr
 291  & int& capacity;& number of discs in a jukebox \cr
 292\noalign{\medskip}
 293  &int& options : 30;& options flags \cr
 294  &unsigned& mc_flags : 2;& media-change buffer flags \cr
 295  & int& use_count;& number of times device is opened\cr
 296  & char& name[20];& name of the device type\cr
 297\}\cr
 298}$$
 299Using this $struct$, a linked list of the registered minor devices is
 300built, using the $next$ field. The device number, the device operations
 301struct and specifications of properties of the drive are stored in this
 302structure.
 303
 304The $mask$ flags can be used to mask out some of the capabilities listed
 305in $ops\to capability$, if a specific drive doesn't support a feature
 306of the driver. The value $speed$ specifies the maximum head-rate of the
 307drive, measured in units of normal audio speed (176\,kB/sec raw data or
 308150\,kB/sec file system data). The value $n_discs$ should reflect the
 309number of discs the drive can hold simultaneously, if it is designed
 310as a juke-box, or otherwise~1. The parameters are declared $const$
 311because they describe properties of the drive, which don't change after
 312registration.
 313
 314A few registers contain variables local to the \cdrom\ drive. The
 315flags $options$ are used to specify how the general \cdrom\ routines
 316should behave. These various flags registers should provide enough
 317flexibility 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
 319the case in the old scheme). The register $mc_flags$ is used to buffer
 320the information from $media_changed()$ to two separate queues. Other
 321data that is specific to a minor drive, can be accessed through $handle$,
 322which can point to a data structure specific to the low-level driver.
 323The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
 324initialized.
 325
 326The intermediate software layer that \cdromc\ forms will perform some
 327additional bookkeeping. The use count of the device (the number of
 328processes that have the device opened) is registered in $use_count$. The
 329function $cdrom_ioctl()$ will verify the appropriate user-memory regions
 330for read and write, and in case a location on the CD is transferred,
 331it will `sanitize' the format by making requests to the low-level
 332drivers in a standard format, and translating all formats between the
 333user-software and low level drivers. This relieves much of the drivers'
 334memory checking and format checking and translation. Also, the necessary
 335structures will be declared on the program stack.
 336
 337The implementation of the functions should be as defined in the
 338following sections. Two functions {\em must\/} be implemented, namely
 339$open()$ and $release()$. Other functions may be omitted, their
 340corresponding capability flags will be cleared upon registration.
 341Generally, a function returns zero on success and negative on error. A
 342function call should return only after the command has completed, but of
 343course 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
 348can be either:
 349\begin{itemize}
 350\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
 351user commands {\tt {dd}} or {\tt {cat}}.  
 352\item[1] Open for $ioctl$ commands, as done by audio-CD playing
 353programs.
 354\end{itemize}
 355Notice that any strategic code (closing tray upon $open()$, etc.)\ is
 356done by the calling routine in \cdromc, so the low-level routine
 357should only be concerned with proper initialization, such as spinning
 358up the disc, etc. % and device-use count
 359
 360
 361\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
 362
 363
 364Device-specific actions should be taken such as spinning down the device.
 365However, strategic actions such as ejection of the tray, or unlocking
 366the door, should be left over to the general routine $cdrom_release()$.
 367This 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
 372The function $drive_status$, if implemented, should provide
 373information on the status of the drive (not the status of the disc,
 374which 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$$
 377\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
 378CDS_NO_INFO& no information available\cr
 379CDS_NO_DISC& no disc is inserted, tray is closed\cr
 380CDS_TRAY_OPEN& tray is opened\cr
 381CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
 382CDS_DISC_OK& a disc is loaded and everything is fine\cr
 383}
 384$$
 385
 386\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
 387
 388This function is very similar to the original function in $struct\ 
 389file_operations$. It returns 1 if the medium of the device $cdi\to
 390dev$ 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
 392ignored for single-disc drives.  Note that by `re-routing' this
 393function through $cdrom_media_changed()$, we can implement separate
 394queues for the VFS and a new $ioctl()$ function that can report device
 395changes to software (\eg, an auto-mounting daemon).
 396
 397\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
 398
 399This function, if implemented, should control the tray movement. (No
 400other function should control this.) The parameter $position$ controls
 401the desired direction of movement:
 402\begin{itemize}
 403\item[0] Close tray
 404\item[1] Open tray
 405\end{itemize}
 406This function returns 0 upon success, and a non-zero value upon
 407error. Note that if the tray is already in the desired position, no
 408action need be taken, and the return value should be 0. 
 409
 410\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
 411
 412This function (and no other code) controls locking of the door, if the
 413drive allows this. The value of $lock$ controls the desired locking
 414state:
 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}
 419This function returns 0 upon success, and a non-zero value upon
 420error. Note that if the door is already in the requested state, no
 421action need be taken, and the return value should be 0. 
 422
 423\subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
 424
 425Some \cdrom\ drives are capable of changing their head-speed. There
 426are several reasons for changing the speed of a \cdrom\ drive. Badly
 427pressed \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
 429common).  It has been reported that these drives can make reading
 430errors at these high speeds, reducing the speed can prevent data loss
 431in these circumstances.  Finally, some of these drives can
 432make 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
 437This function specifies the speed at which data is read or audio is
 438played back. The value of $speed$ specifies the head-speed of the
 439drive, measured in units of standard cdrom speed (176\,kB/sec raw data
 440or 150\,kB/sec file system data). So to request that a \cdrom\ drive
 441operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
 442with $speed=2$. The special value `0' means `auto-selection', \ie,
 443maximum data-rate or real-time audio rate. If the drive doesn't have
 444this `auto-selection' capability, the decision should be made on the
 445current disc loaded and the return value should be positive. A negative
 446return value indicates an error.
 447
 448\subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
 449
 450If the drive can store multiple discs (a juke-box) this function
 451will perform disc selection. It should return the number of the
 452selected disc on success, a negative value on error. Currently, only
 453the 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
 458This function should implement the old corresponding $ioctl()$. For
 459device $cdi\to dev$, the start of the last session of the current disc
 460should be returned in the pointer argument $ms_info$. Note that
 461routines in \cdromc\ have sanitized this argument: its requested
 462format will {\em always\/} be of the type $CDROM_LBA$ (linear block
 463addressing mode), whatever the calling software requested. But
 464sanitization goes even further: the low-level implementation may
 465return the requested information in $CDROM_MSF$ format if it wishes so
 466(setting the $ms_info\rightarrow addr_format$ field appropriately, of
 467course) and the routines in \cdromc\ will make the transformation if
 468necessary. The return value is 0 upon success.
 469
 470\subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
 471  cdrom_mcn * mcn)$}
 472
 473Some discs carry a `Media Catalog Number' (MCN), also called
 474`Universal Product Code' (UPC). This number should reflect the number
 475that is generally found in the bar-code on the product. Unfortunately,
 476the few discs that carry such a number on the disc don't even use the
 477same format. The return argument to this function is a pointer to a
 478pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
 479expected as a 13-character string, terminated by a null-character.
 480
 481\subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
 482
 483This call should perform a hard-reset on the drive (although in
 484circumstances that a hard-reset is necessary, a drive may very well not
 485listen to commands anymore). Preferably, control is returned to the
 486caller only after the drive has finished resetting. If the drive is no
 487longer listening, it may be wise for the underlying low-level cdrom
 488driver to time out.
 489
 490\subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
 491  int\ cmd, void * arg)$}
 492
 493Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
 494implemented by the routines described above, and hence the function
 495$cdrom_ioctl$ will use those. However, most $ioctl$s deal with
 496audio-control. We have decided to leave these to be accessed through a
 497single function, repeating the arguments $cmd$ and $arg$. Note that
 498the latter is of type $void*{}$, rather than $unsigned\ long\
 499int$. The routine $cdrom_ioctl()$ does do some useful things,
 500though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
 501Seconds, Frames) for all audio calls. It also verifies the memory
 502location of $arg$, and reserves stack-memory for the argument. This
 503makes implementation of the $audio_ioctl()$ much simpler than in the
 504old driver scheme. For example, you may look up the function
 505$cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
 506this documentation. 
 507
 508An unimplemented ioctl should return $-ENOSYS$, but a harmless request
 509(\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
 510errors should be according to the standards, whatever they are. When
 511an error is returned by the low-level driver, the \UCD\ tries whenever
 512possible to return the error code to the calling program. (We may decide
 513to sanitize the return value in $cdrom_ioctl()$ though, in order to
 514guarantee 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
 519Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
 520they are introduced to service some capabilities of certain drives. In
 521fact, there are 6 different $ioctl$s for reading data, either in some
 522particular kind of format, or audio data. Not many drives support
 523reading audio tracks as data, I believe this is because of protection
 524of copyrights of artists. Moreover, I think that if audio-tracks are
 525supported, it should be done through the VFS and not via $ioctl$s. A
 526problem here could be the fact that audio-frames are 2352 bytes long,
 527so 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
 529bend their backs to cope with this incoherence (to which I would be
 530opposed).  Furthermore, it is very difficult for the hardware to find
 531the exact frame boundaries, since there are no synchronization headers
 532in audio frames.  Once these issues are resolved, this code should be
 533standardized in \cdromc.
 534
 535Because there are so many $ioctl$s that seem to be introduced to
 536satisfy certain drivers,\footnote{Is there software around that
 537  actually uses these? I'd be interested!} any `non-standard' $ioctl$s
 538are routed through the call $dev_ioctl()$. In principle, `private'
 539$ioctl$s should be numbered after the device's major number, and not
 540the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
 541non-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
 549Instead of just implementing some $ioctl$ calls, the interface in
 550\cdromc\ supplies the possibility to indicate the {\em capabilities\/}
 551of a \cdrom\ drive. This can be done by ORing any number of
 552capability-constants that are defined in \cdromh\ at the registration
 553phase. Currently, the capabilities are any of:
 554$$
 555\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
 556CDC_CLOSE_TRAY& can close tray by software control\cr
 557CDC_OPEN_TRAY& can open tray\cr
 558CDC_LOCK& can lock and unlock the door\cr
 559CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
 560CDC_SELECT_DISC& drive is juke-box\cr
 561CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
 562CDC_MCN& can read Media Catalog Number\cr
 563CDC_MEDIA_CHANGED& can report if disc has changed\cr
 564CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
 565CDC_RESET& hard reset device\cr
 566CDC_IOCTLS& driver has non-standard ioctls\cr
 567CDC_DRIVE_STATUS& driver implements drive status\cr
 568}
 569$$
 570The capability flag is declared $const$, to prevent drivers from
 571accidentally tampering with the contents. The capability fags actually
 572inform \cdromc\ of what the driver can do. If the drive found
 573by the driver does not have the capability, is can be masked out by
 574the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
 575driver has implemented the code for loading and ejecting \cdrom's, and
 576hence 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
 578hence for this drive the $cdrom_device_info$ struct will have set
 579the $CDC_CLOSE_TRAY$ bit in $mask$.
 580
 581In the file \cdromc\ you will encounter many constructions of the type
 582$$\it
 583if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 
 584   \mathrel{\&} CDC_<capability>) \ldots
 585$$
 586There is no $ioctl$ to set the mask\dots The reason is that
 587I think it is better to control the {\em behavior\/} rather than the
 588{\em capabilities}.
 589
 590\subsection{Options}
 591
 592A final flag register controls the {\em behavior\/} of the \cdrom\
 593drives, in order to satisfy different users' wishes, hopefully
 594independently of the ideas of the respective author who happened to
 595have made the drive's support available to the \linux\ community. The
 596current behavior options are:
 597$$
 598\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
 599CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
 600CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
 601CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
 602 purpose for $open()$\cr
 603CDO_LOCK& try to lock door if device is opened\cr
 604CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
 605}
 606$$
 607
 608The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
 609CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
 610interface and software standards. Before you protest, there are two
 611new $ioctl$s implemented in \cdromc, that allow you to control the
 612behavior by software. These are:
 613$$
 614\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
 615CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
 616CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
 617}
 618$$
 619One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
 620newsection we explain what the need for this option is.
 621
 622A software package {\tt setcd}, available from the Debian distribution
 623and {\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
 627Traditionally, Unix devices can be used in two different `modes',
 628either by reading/writing to the device file, or by issuing
 629controlling commands to the device, by the device's $ioctl()$
 630call. The problem with \cdrom\ drives, is that they can be used for
 631two entirely different purposes. One is to mount removable
 632file systems, \cdrom s, the other is to play audio CD's. Audio commands
 633are implemented entirely through $ioctl$s, presumably because the
 634first implementation (SUN?) has been such. In principle there is
 635nothing wrong with this, but a good control of the `CD player' demands
 636that the device can {\em always\/} be opened in order to give the
 637$ioctl$ commands, regardless of the state the drive is in. 
 638
 639On the other hand, when used as a removable-media disc drive (what the
 640original purpose of \cdrom s is) we would like to make sure that the
 641disc drive is ready for operation upon opening the device. In the old
 642scheme, some \cdrom\ drivers don't do any integrity checking, resulting
 643in a number of i/o errors reported by the VFS to the kernel when an
 644attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
 645particularly elegant way to find out that there is no \cdrom\ inserted;
 646it more-or-less looks like the old IBM-PC trying to read an empty floppy
 647drive for a couple of seconds, after which the system complains it
 648can't read from it. Nowadays we can {\em sense\/} the existence of a
 649removable medium in a drive, and we believe we should exploit that
 650fact. An integrity check on opening of the device, that verifies the
 651availability of a \cdrom\ and its correct type (data), would be
 652desirable.
 653
 654These two ways of using a \cdrom\ drive, principally for data and
 655secondarily for playing audio discs, have different demands for the
 656behavior of the $open()$ call. Audio use simply wants to open the
 657device in order to get a file handle which is needed for issuing
 658$ioctl$ commands, while data use wants to open for correct and
 659reliable data transfer. The only way user programs can indicate what
 660their {\em purpose\/} of opening the device is, is through the $flags$
 661parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
 662implemented (some drivers implement checking for write-related flags,
 663but this is not strictly necessary if the device file has correct
 664permission 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
 668We therefore propose to use the flag $O_NONBLOCK$ to indicate
 669that the device is opened just for issuing $ioctl$
 670commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
 671subsequent calls to the device don't cause the calling process to
 672wait. We could interpret this as ``don't wait until someone has
 673inserted some valid data-\cdrom.'' Thus, our proposal of the
 674implementation 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
 677for data transfer, and the return value will be 0 only upon successful
 678initialization of the transfer. The call may even induce some actions
 679on the \cdrom, such as closing the tray.  
 680\item If the option flag $O_NONBLOCK$ is set, opening will always be
 681successful, unless the whole device doesn't exist. The drive will take
 682no actions whatsoever. 
 683\end{itemize}
 684
 685\subsection{And what about standards?}
 686
 687You might hesitate to accept this proposal as it comes from the
 688\linux\ community, and not from some standardizing institute. What
 689about SUN, SGI, HP and all those other Unix and hardware vendors?
 690Well, these companies are in the lucky position that they generally
 691control both the hardware and software of their supported products,
 692and are large enough to set their own standard. They do not have to
 693deal with a dozen or more different, competing hardware
 694configurations.\footnote{Incidentally, I think that SUN's approach to
 695mounting \cdrom s is very good in origin: under Solaris a
 696volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
 697{/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
 698further and have {\em every\/} \cdrom\ on the local area network be
 699mounted at the similar location, \ie, no matter in which particular
 700machine you insert a \cdrom, it will always appear at the same
 701position in the directory tree, on every system. When I wanted to
 702implement such a user-program for \linux, I came across the
 703differences in behavior of the various drivers, and the need for an
 704$ioctl$ informing about media changes.}
 705
 706We believe that using $O_NONBLOCK$ to indicate that a device is being opened
 707for $ioctl$ commands only can be easily introduced in the \linux\
 708community. All the CD-player authors will have to be informed, we can
 709even send in our own patches to the programs. The use of $O_NONBLOCK$
 710has most likely no influence on the behavior of the CD-players on
 711other operating systems than \linux. Finally, a user can always revert
 712to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
 713CDO_USE_FFLAGS)$. 
 714
 715\subsection{The preferred strategy of $open()$}
 716
 717The routines in \cdromc\ are designed in such a way that run-time
 718configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
 719can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
 720modes of operation can be set:
 721\begin{description}
 722\item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
 723is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
 724future.) If the device is not yet opened by any other process, and if
 725the device is being opened for data ($O_NONBLOCK$ is not set) and the
 726tray is found to be open, an attempt to close the tray is made. Then,
 727it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
 728set, that it contains tracks of type `data mode 1.' Only if all tests
 729are passed is the return value zero. The door is locked to prevent file
 730system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
 731set), 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
 733mimics the behavior of the current sbpcd-driver. The option flags are
 734ignored, the tray is closed on the first open, if necessary. Similarly,
 735the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
 736it is automatically ejected, such that the user can replace it.
 737\end{description} 
 738We hope that these option can convince everybody (both driver
 739maintainers and user program developers) to adopt the new \cdrom\
 740driver scheme and option flag interpretation.
 741
 742\newsection{Description of routines in \cdromc}
 743
 744Only a few routines in \cdromc\ are exported to the drivers. In this
 745new section we will discuss these, as well as the functions that `take
 746over' the \cdrom\ interface to the kernel. The header file belonging
 747to \cdromc\ is called \cdromh. Formerly, some of the contents of this
 748file were placed in the file {\tt {ucdrom.h}}, but this file has now been
 749merged back into \cdromh.
 750
 751\subsection{$Struct\ file_operations\ cdrom_fops$}
 752
 753The contents of this structure were described in section~\ref{cdrom.c}.
 754A pointer to this structure is assigned to the $fops$ field
 755of the $struct gendisk$.
 756
 757\subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
 758
 759This function is used in about the same way one registers $cdrom_fops$
 760with the kernel, the device operations and information structures,
 761as described in section~\ref{cdrom.c}, should be registered with the
 762\UCD:
 763$$
 764register_cdrom(\&<device>_info));
 765$$
 766This function returns zero upon success, and non-zero upon
 767failure. The structure $<device>_info$ should have a pointer to the
 768driver's $<device>_dops$, as in 
 769$$
 770\vbox{\halign{&$#$\hfil\cr
 771struct\ &cdrom_device_info\ <device>_info = \{\cr
 772& <device>_dops;\cr
 773&\ldots\cr
 774\}\cr
 775}}$$
 776Note that a driver must have one static structure, $<device>_dops$, while
 777it may have as many structures $<device>_info$ as there are minor devices
 778active. $Register_cdrom()$ builds a linked list from these. 
 779
 780\subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
 781
 782Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
 783the minor device from the list. If it was the last registered minor for
 784the low-level driver, this disconnects the registered device-operation
 785routines from the \cdrom\ interface. This function returns zero upon
 786success, and non-zero upon failure.
 787
 788\subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
 789
 790This function is not called directly by the low-level drivers, it is
 791listed in the standard $cdrom_fops$. If the VFS opens a file, this
 792function becomes active. A strategy is implemented in this routine,
 793taking care of all capabilities and options that are set in the
 794$cdrom_device_ops$ connected to the device. Then, the program flow is
 795transferred to the device_dependent $open()$ call.
 796
 797\subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
 798*fp)$}
 799
 800This function implements the reverse-logic of $cdrom_open()$, and then
 801calls the device-dependent $release()$ routine. When the use-count has
 802reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
 803and $invalidate_buffers(dev)$.
 804
 805
 806\subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
 807unsigned\ int\ cmd, unsigned\ long\ arg)$}
 808\label{cdrom-ioctl}
 809
 810This function handles all the standard $ioctl$ requests for \cdrom\
 811devices in a uniform way. The different calls fall into three
 812categories: $ioctl$s that can be directly implemented by device
 813operations, ones that are routed through the call $audio_ioctl()$, and
 814the remaining ones, that are presumable device-dependent. Generally, a
 815negative return value indicates an error.
 816
 817\subsubsection{Directly implemented $ioctl$s}
 818\label{ioctl-direct}
 819
 820The following `old' \cdrom-$ioctl$s are implemented by directly
 821calling device-operations in $cdrom_device_ops$, if implemented and
 822not 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
 828tray on first open) and auto-eject (eject on last release), otherwise
 829set 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
 836The following set of $ioctl$s are all implemented through a call to
 837the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
 838allocation are performed in $cdrom_ioctl()$, and also sanitization of
 839address format ($CDROM_LBA$/$CDROM_MSF$) is done.
 840\begin{description}
 841\item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
 842cdrom_subchnl *{}$.
 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
 846specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
 847\item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
 848Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
 849\item[CDROMPLAYTRKIND] Play audio fragment in track-index format
 850delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
 851\item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
 852cdrom_volctrl *{}$.
 853\item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
 854cdrom_volctrl *{}$.
 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
 863The following $ioctl$s have been introduced to allow user programs to
 864control the behavior of individual \cdrom\ devices. New $ioctl$
 865commands can be identified by the underscores in their names.
 866\begin{description}
 867\item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
 868option flag register after modification. Use  $arg = \rm0$ for reading
 869the 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
 950Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
 951if 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
1007Thanks to all the people involved.  First, Erik Andersen, who has
1008taken over the torch in maintaining \cdromc\ and integrating much
1009\cdrom-related code in the 2.1-kernel.  Thanks to Scott Snyder and
1010Gerd Knorr, who were the first to implement this interface for SCSI
1011and IDE-CD drivers and added many ideas for extension of the data
1012structures relative to kernel~2.0.  Further thanks to Heiko Ei{\sz}feldt,
1013Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
1014Kroll, the \linux\ \cdrom\ device driver developers who were kind
1015enough to give suggestions and criticisms during the writing. Finally
1016of course, I want to thank Linus Torvalds for making this possible in
1017the first place.
1018
1019\vfill
1020$ \version\ $
1021\eject
1022\end{document}
1023
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