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1 \documentclass{article} 2 \def\version{$Id: cdrom-standard.tex,v 1.9 1997/12/28 15:42:49 david Exp $} 3 \newcommand{\newsection}[1]{\newpage\section{#1}} 4 5 \evensidemargin=0pt 6 \oddsidemargin=0pt 7 \topmargin=-\headheight \advance\topmargin by -\headsep 8 \textwidth=15.99cm \textheight=24.62cm % normal A4, 1'' margin 9 10 \def\linux{{\sc Linux}} 11 \def\cdrom{{\sc cd-rom}} 12 \def\UCD{{\sc Uniform cd-rom Driver}} 13 \def\cdromc{{\tt {cdrom.c}}} 14 \def\cdromh{{\tt {cdrom.h}}} 15 \def\fo{\sl} % foreign words 16 \def\ie{{\fo i.e.}} 17 \def\eg{{\fo e.g.}} 18 19 \everymath{\it} \everydisplay{\it} 20 \catcode `\_=\active \def_{\_\penalty100 } 21 \catcode`\<=\active \def<#1>{{\langle\hbox{\rm#1}\rangle}} 22 23 \begin{document} 24 \title{A \linux\ \cdrom\ standard} 25 \author{David van Leeuwen\\{\normalsize\tt david@ElseWare.cistron.nl} 26 \\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}} 27 \\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}} 28 \date{12 March 1999} 29 30 \maketitle 31 32 \newsection{Introduction} 33 34 \linux\ is probably the Unix-like operating system that supports 35 the widest variety of hardware devices. The reasons for this are 36 presumably 37 \begin{itemize} 38 \item 39 The large list of hardware devices available for the many platforms 40 that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.) 41 \item 42 The open design of the operating system, such that anybody can write a 43 driver for \linux. 44 \item 45 There is plenty of source code around as examples of how to write a driver. 46 \end{itemize} 47 The openness of \linux, and the many different types of available 48 hardware has allowed \linux\ to support many different hardware devices. 49 Unfortunately, the very openness that has allowed \linux\ to support 50 all these different devices has also allowed the behavior of each 51 device driver to differ significantly from one device to another. 52 This divergence of behavior has been very significant for \cdrom\ 53 devices; the way a particular drive reacts to a `standard' $ioctl()$ 54 call varies greatly from one device driver to another. To avoid making 55 their drivers totally inconsistent, the writers of \linux\ \cdrom\ 56 drivers generally created new device drivers by understanding, copying, 57 and then changing an existing one. Unfortunately, this practice did not 58 maintain uniform behavior across all the \linux\ \cdrom\ drivers. 59 60 This document describes an effort to establish Uniform behavior across 61 all the different \cdrom\ device drivers for \linux. This document also 62 defines the various $ioctl$s, and how the low-level \cdrom\ device 63 drivers should implement them. Currently (as of the \linux\ 2.1.$x$ 64 development kernels) several low-level \cdrom\ device drivers, including 65 both IDE/ATAPI and SCSI, now use this Uniform interface. 66 67 When the \cdrom\ was developed, the interface between the \cdrom\ drive 68 and the computer was not specified in the standards. As a result, many 69 different \cdrom\ interfaces were developed. Some of them had their 70 own proprietary design (Sony, Mitsumi, Panasonic, Philips), other 71 manufacturers adopted an existing electrical interface and changed 72 the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply 73 adapted their drives to one or more of the already existing electrical 74 interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and 75 most of the `NoName' manufacturers). In cases where a new drive really 76 brought its own interface or used its own command set and flow control 77 scheme, either a separate driver had to be written, or an existing 78 driver had to be enhanced. History has delivered us \cdrom\ support for 79 many of these different interfaces. Nowadays, almost all new \cdrom\ 80 drives are either IDE/ATAPI or SCSI, and it is very unlikely that any 81 manufacturer will create a new interface. Even finding drives for the 82 old proprietary interfaces is getting difficult. 83 84 When (in the 1.3.70's) I looked at the existing software interface, 85 which was expressed through \cdromh, it appeared to be a rather wild 86 set of commands and data formats.\footnote{I cannot recollect what 87 kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the 88 latest kernel that I was indirectly involved in.} It seemed that many 89 features of the software interface had been added to accommodate the 90 capabilities of a particular drive, in an {\fo ad hoc\/} manner. More 91 importantly, it appeared that the behavior of the `standard' commands 92 was different for most of the different drivers: \eg, some drivers 93 close the tray if an $open()$ call occurs when the tray is open, while 94 others do not. Some drivers lock the door upon opening the device, to 95 prevent an incoherent file system, but others don't, to allow software 96 ejection. Undoubtedly, the capabilities of the different drives vary, 97 but even when two drives have the same capability their drivers' 98 behavior was usually different. 99 100 I decided to start a discussion on how to make all the \linux\ \cdrom\ 101 drivers behave more uniformly. I began by contacting the developers of 102 the many \cdrom\ drivers found in the \linux\ kernel. Their reactions 103 encouraged me to write the \UCD\ which this document is intended to 104 describe. The implementation of the \UCD\ is in the file \cdromc. This 105 driver is intended to be an additional software layer that sits on top 106 of the low-level device drivers for each \cdrom\ drive. By adding this 107 additional layer, it is possible to have all the different \cdrom\ 108 devices behave {\em exactly\/} the same (insofar as the underlying 109 hardware will allow). 110 111 The goal of the \UCD\ is {\em not\/} to alienate driver developers who 112 have not yet taken steps to support this effort. The goal of \UCD\ is 113 simply to give people writing application programs for \cdrom\ drives 114 {\em one\/} \linux\ \cdrom\ interface with consistent behavior for all 115 \cdrom\ devices. In addition, this also provides a consistent interface 116 between the low-level device driver code and the \linux\ kernel. Care 117 is taken that 100\,\% compatibility exists with the data structures and 118 programmer's interface defined in \cdromh. This guide was written to 119 help \cdrom\ driver developers adapt their code to use the \UCD\ code 120 defined in \cdromc. 121 122 Personally, I think that the most important hardware interfaces are 123 the IDE/ATAPI drives and, of course, the SCSI drives, but as prices 124 of hardware drop continuously, it is also likely that people may have 125 more than one \cdrom\ drive, possibly of mixed types. It is important 126 that these drives behave in the same way. In December 1994, one of the 127 cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary 128 drive. In the months that I was busy writing a \linux\ driver for it, 129 proprietary drives became obsolete and IDE/ATAPI drives became the 130 standard. At the time of the last update to this document (November 131 1997) it is becoming difficult to even {\em find} anything less than a 132 16 speed \cdrom\ drive, and 24 speed drives are common. 133 134 \newsection{Standardizing through another software level} 135 \label{cdrom.c} 136 137 At the time this document was conceived, all drivers directly 138 implemented the \cdrom\ $ioctl()$ calls through their own routines. This 139 led to the danger of different drivers forgetting to do important things 140 like checking that the user was giving the driver valid data. More 141 importantly, this led to the divergence of behavior, which has already 142 been discussed. 143 144 For this reason, the \UCD\ was created to enforce consistent \cdrom\ 145 drive behavior, and to provide a common set of services to the various 146 low-level \cdrom\ device drivers. The \UCD\ now provides another 147 software-level, that separates the $ioctl()$ and $open()$ implementation 148 from the actual hardware implementation. Note that this effort has 149 made few changes which will affect a user's application programs. The 150 greatest change involved moving the contents of the various low-level 151 \cdrom\ drivers' header files to the kernel's cdrom directory. This was 152 done to help ensure that the user is only presented with only one cdrom 153 interface, the interface defined in \cdromh. 154 155 \cdrom\ drives are specific enough (\ie, different from other 156 block-devices such as floppy or hard disc drives), to define a set 157 of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$. 158 These operations are different from the classical block-device file 159 operations, $<block-device>_fops$. 160 161 The routines for the \UCD\ interface level are implemented in the file 162 \cdromc. In this file, the \UCD\ interfaces with the kernel as a block 163 device by registering the following general $struct\ file_operations$: 164 $$ 165 \halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 166 struct& file_operations\ cdrom_fops = \{\hidewidth\cr 167 &NULL, & lseek \cr 168 &block_read, & read---general block-dev read \cr 169 &block_write, & write---general block-dev write \cr 170 &NULL, & readdir \cr 171 &NULL, & select \cr 172 &cdrom_ioctl, & ioctl \cr 173 &NULL, & mmap \cr 174 &cdrom_open, & open \cr 175 &cdrom_release, & release \cr 176 &NULL, & fsync \cr 177 &NULL, & fasync \cr 178 &cdrom_media_changed, & media change \cr 179 &NULL & revalidate \cr 180 \};\cr 181 } 182 $$ 183 184 Every active \cdrom\ device shares this $struct$. The routines 185 declared above are all implemented in \cdromc, since this file is the 186 place where the behavior of all \cdrom-devices is defined and 187 standardized. The actual interface to the various types of \cdrom\ 188 hardware is still performed by various low-level \cdrom-device 189 drivers. These routines simply implement certain {\em capabilities\/} 190 that are common to all \cdrom\ (and really, all removable-media 191 devices). 192 193 Registration of a low-level \cdrom\ device driver is now done through 194 the general routines in \cdromc, not through the Virtual File System 195 (VFS) any more. The interface implemented in \cdromc\ is carried out 196 through two general structures that contain information about the 197 capabilities of the driver, and the specific drives on which the 198 driver operates. The structures are: 199 \begin{description} 200 \item[$cdrom_device_ops$] 201 This structure contains information about the low-level driver for a 202 \cdrom\ device. This structure is conceptually connected to the major 203 number of the device (although some drivers may have different 204 major numbers, as is the case for the IDE driver). 205 \item[$cdrom_device_info$] 206 This structure contains information about a particular \cdrom\ drive, 207 such as its device name, speed, etc. This structure is conceptually 208 connected to the minor number of the device. 209 \end{description} 210 211 Registering a particular \cdrom\ drive with the \UCD\ is done by the 212 low-level device driver though a call to: 213 $$register_cdrom(struct\ cdrom_device_info * <device>_info) 214 $$ 215 The device information structure, $<device>_info$, contains all the 216 information needed for the kernel to interface with the low-level 217 \cdrom\ device driver. One of the most important entries in this 218 structure is a pointer to the $cdrom_device_ops$ structure of the 219 low-level driver. 220 221 The device operations structure, $cdrom_device_ops$, contains a list 222 of pointers to the functions which are implemented in the low-level 223 device driver. When \cdromc\ accesses a \cdrom\ device, it does it 224 through the functions in this structure. It is impossible to know all 225 the capabilities of future \cdrom\ drives, so it is expected that this 226 list may need to be expanded from time to time as new technologies are 227 developed. For example, CD-R and CD-R/W drives are beginning to become 228 popular, and support will soon need to be added for them. For now, the 229 current $struct$ is: 230 $$ 231 \halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}& 232 $/*$ \rm# $*/$\hfil\cr 233 struct& cdrom_device_ops\ \{ \hidewidth\cr 234 &int& (* open)(struct\ cdrom_device_info *, int)\cr 235 &void& (* release)(struct\ cdrom_device_info *);\cr 236 &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr 237 &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 238 &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr 239 &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr 240 &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr 241 &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr 242 &int& (* get_last_session) (struct\ cdrom_device_info *, 243 struct\ cdrom_multisession *{});\cr 244 &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr 245 &int& (* reset)(struct\ cdrom_device_info *);\cr 246 &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 247 void *{});\cr 248 &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 249 unsigned\ long);\cr 250 \noalign{\medskip} 251 &const\ int& capability;& capability flags \cr 252 \};\cr 253 } 254 $$ 255 When a low-level device driver implements one of these capabilities, 256 it should add a function pointer to this $struct$. When a particular 257 function is not implemented, however, this $struct$ should contain a 258 NULL instead. The $capability$ flags specify the capabilities of the 259 \cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive 260 is registered with the \UCD. 261 262 Note that most functions have fewer parameters than their 263 $blkdev_fops$ counterparts. This is because very little of the 264 information in the structures $inode$ and $file$ is used. For most 265 drivers, the main parameter is the $struct$ $cdrom_device_info$, from 266 which the major and minor number can be extracted. (Most low-level 267 \cdrom\ drivers don't even look at the major and minor number though, 268 since many of them only support one device.) This will be available 269 through $dev$ in $cdrom_device_info$ described below. 270 271 The drive-specific, minor-like information that is registered with 272 \cdromc, currently contains the following fields: 273 $$ 274 \halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}& 275 $/*$ \rm# $*/$\hfil\cr 276 struct& cdrom_device_info\ \{ \hidewidth\cr 277 & struct\ cdrom_device_ops *& ops;& device operations for this major\cr 278 & struct\ cdrom_device_info *& next;& next device_info for this major\cr 279 & void *& handle;& driver-dependent data\cr 280 \noalign{\medskip} 281 & kdev_t& dev;& device number (incorporates minor)\cr 282 & int& mask;& mask of capability: disables them \cr 283 & int& speed;& maximum speed for reading data \cr 284 & int& capacity;& number of discs in a jukebox \cr 285 \noalign{\medskip} 286 &int& options : 30;& options flags \cr 287 &unsigned& mc_flags : 2;& media-change buffer flags \cr 288 & int& use_count;& number of times device is opened\cr 289 & char& name[20];& name of the device type\cr 290 \}\cr 291 }$$ 292 Using this $struct$, a linked list of the registered minor devices is 293 built, using the $next$ field. The device number, the device operations 294 struct and specifications of properties of the drive are stored in this 295 structure. 296 297 The $mask$ flags can be used to mask out some of the capabilities listed 298 in $ops\to capability$, if a specific drive doesn't support a feature 299 of the driver. The value $speed$ specifies the maximum head-rate of the 300 drive, measured in units of normal audio speed (176\,kB/sec raw data or 301 150\,kB/sec file system data). The value $n_discs$ should reflect the 302 number of discs the drive can hold simultaneously, if it is designed 303 as a juke-box, or otherwise~1. The parameters are declared $const$ 304 because they describe properties of the drive, which don't change after 305 registration. 306 307 A few registers contain variables local to the \cdrom\ drive. The 308 flags $options$ are used to specify how the general \cdrom\ routines 309 should behave. These various flags registers should provide enough 310 flexibility to adapt to the different users' wishes (and {\em not\/} the 311 `arbitrary' wishes of the author of the low-level device driver, as is 312 the case in the old scheme). The register $mc_flags$ is used to buffer 313 the information from $media_changed()$ to two separate queues. Other 314 data that is specific to a minor drive, can be accessed through $handle$, 315 which can point to a data structure specific to the low-level driver. 316 The fields $use_count$, $next$, $options$ and $mc_flags$ need not be 317 initialized. 318 319 The intermediate software layer that \cdromc\ forms will perform some 320 additional bookkeeping. The use count of the device (the number of 321 processes that have the device opened) is registered in $use_count$. The 322 function $cdrom_ioctl()$ will verify the appropriate user-memory regions 323 for read and write, and in case a location on the CD is transferred, 324 it will `sanitize' the format by making requests to the low-level 325 drivers in a standard format, and translating all formats between the 326 user-software and low level drivers. This relieves much of the drivers' 327 memory checking and format checking and translation. Also, the necessary 328 structures will be declared on the program stack. 329 330 The implementation of the functions should be as defined in the 331 following sections. Two functions {\em must\/} be implemented, namely 332 $open()$ and $release()$. Other functions may be omitted, their 333 corresponding capability flags will be cleared upon registration. 334 Generally, a function returns zero on success and negative on error. A 335 function call should return only after the command has completed, but of 336 course waiting for the device should not use processor time. 337 338 \subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$} 339 340 $Open()$ should try to open the device for a specific $purpose$, which 341 can be either: 342 \begin{itemize} 343 \item[0] Open for reading data, as done by {\tt {mount()}} (2), or the 344 user commands {\tt {dd}} or {\tt {cat}}. 345 \item[1] Open for $ioctl$ commands, as done by audio-CD playing 346 programs. 347 \end{itemize} 348 Notice that any strategic code (closing tray upon $open()$, etc.)\ is 349 done by the calling routine in \cdromc, so the low-level routine 350 should only be concerned with proper initialization, such as spinning 351 up the disc, etc. % and device-use count 352 353 354 \subsection{$Void\ release(struct\ cdrom_device_info * cdi)$} 355 356 357 Device-specific actions should be taken such as spinning down the device. 358 However, strategic actions such as ejection of the tray, or unlocking 359 the door, should be left over to the general routine $cdrom_release()$. 360 This is the only function returning type $void$. 361 362 \subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$} 363 \label{drive status} 364 365 The function $drive_status$, if implemented, should provide 366 information on the status of the drive (not the status of the disc, 367 which may or may not be in the drive). If the drive is not a changer, 368 $slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 369 $$ 370 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 371 CDS_NO_INFO& no information available\cr 372 CDS_NO_DISC& no disc is inserted, tray is closed\cr 373 CDS_TRAY_OPEN& tray is opened\cr 374 CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr 375 CDS_DISC_OK& a disc is loaded and everything is fine\cr 376 } 377 $$ 378 379 \subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$} 380 381 This function is very similar to the original function in $struct\ 382 file_operations$. It returns 1 if the medium of the device $cdi\to 383 dev$ has changed since the last call, and 0 otherwise. The parameter 384 $disc_nr$ identifies a specific slot in a juke-box, it should be 385 ignored for single-disc drives. Note that by `re-routing' this 386 function through $cdrom_media_changed()$, we can implement separate 387 queues for the VFS and a new $ioctl()$ function that can report device 388 changes to software (\eg, an auto-mounting daemon). 389 390 \subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$} 391 392 This function, if implemented, should control the tray movement. (No 393 other function should control this.) The parameter $position$ controls 394 the desired direction of movement: 395 \begin{itemize} 396 \item[0] Close tray 397 \item[1] Open tray 398 \end{itemize} 399 This function returns 0 upon success, and a non-zero value upon 400 error. Note that if the tray is already in the desired position, no 401 action need be taken, and the return value should be 0. 402 403 \subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$} 404 405 This function (and no other code) controls locking of the door, if the 406 drive allows this. The value of $lock$ controls the desired locking 407 state: 408 \begin{itemize} 409 \item[0] Unlock door, manual opening is allowed 410 \item[1] Lock door, tray cannot be ejected manually 411 \end{itemize} 412 This function returns 0 upon success, and a non-zero value upon 413 error. Note that if the door is already in the requested state, no 414 action need be taken, and the return value should be 0. 415 416 \subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$} 417 418 Some \cdrom\ drives are capable of changing their head-speed. There 419 are several reasons for changing the speed of a \cdrom\ drive. Badly 420 pressed \cdrom s may benefit from less-than-maximum head rate. Modern 421 \cdrom\ drives can obtain very high head rates (up to $24\times$ is 422 common). It has been reported that these drives can make reading 423 errors at these high speeds, reducing the speed can prevent data loss 424 in these circumstances. Finally, some of these drives can 425 make an annoyingly loud noise, which a lower speed may reduce. %Finally, 426 %although the audio-low-pass filters probably aren't designed for it, 427 %more than real-time playback of audio might be used for high-speed 428 %copying of audio tracks. 429 430 This function specifies the speed at which data is read or audio is 431 played back. The value of $speed$ specifies the head-speed of the 432 drive, measured in units of standard cdrom speed (176\,kB/sec raw data 433 or 150\,kB/sec file system data). So to request that a \cdrom\ drive 434 operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$ 435 with $speed=2$. The special value `0' means `auto-selection', \ie, 436 maximum data-rate or real-time audio rate. If the drive doesn't have 437 this `auto-selection' capability, the decision should be made on the 438 current disc loaded and the return value should be positive. A negative 439 return value indicates an error. 440 441 \subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$} 442 443 If the drive can store multiple discs (a juke-box) this function 444 will perform disc selection. It should return the number of the 445 selected disc on success, a negative value on error. Currently, only 446 the ide-cd driver supports this functionality. 447 448 \subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\ 449 cdrom_multisession * ms_info)$} 450 451 This function should implement the old corresponding $ioctl()$. For 452 device $cdi\to dev$, the start of the last session of the current disc 453 should be returned in the pointer argument $ms_info$. Note that 454 routines in \cdromc\ have sanitized this argument: its requested 455 format will {\em always\/} be of the type $CDROM_LBA$ (linear block 456 addressing mode), whatever the calling software requested. But 457 sanitization goes even further: the low-level implementation may 458 return the requested information in $CDROM_MSF$ format if it wishes so 459 (setting the $ms_info\rightarrow addr_format$ field appropriately, of 460 course) and the routines in \cdromc\ will make the transformation if 461 necessary. The return value is 0 upon success. 462 463 \subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\ 464 cdrom_mcn * mcn)$} 465 466 Some discs carry a `Media Catalog Number' (MCN), also called 467 `Universal Product Code' (UPC). This number should reflect the number 468 that is generally found in the bar-code on the product. Unfortunately, 469 the few discs that carry such a number on the disc don't even use the 470 same format. The return argument to this function is a pointer to a 471 pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is 472 expected as a 13-character string, terminated by a null-character. 473 474 \subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$} 475 476 This call should perform a hard-reset on the drive (although in 477 circumstances that a hard-reset is necessary, a drive may very well not 478 listen to commands anymore). Preferably, control is returned to the 479 caller only after the drive has finished resetting. If the drive is no 480 longer listening, it may be wise for the underlying low-level cdrom 481 driver to time out. 482 483 \subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\ 484 int\ cmd, void * arg)$} 485 486 Some of the \cdrom-$ioctl$s defined in \cdromh\ can be 487 implemented by the routines described above, and hence the function 488 $cdrom_ioctl$ will use those. However, most $ioctl$s deal with 489 audio-control. We have decided to leave these to be accessed through a 490 single function, repeating the arguments $cmd$ and $arg$. Note that 491 the latter is of type $void*{}$, rather than $unsigned\ long\ 492 int$. The routine $cdrom_ioctl()$ does do some useful things, 493 though. It sanitizes the address format type to $CDROM_MSF$ (Minutes, 494 Seconds, Frames) for all audio calls. It also verifies the memory 495 location of $arg$, and reserves stack-memory for the argument. This 496 makes implementation of the $audio_ioctl()$ much simpler than in the 497 old driver scheme. For example, you may look up the function 498 $cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with 499 this documentation. 500 501 An unimplemented ioctl should return $-ENOSYS$, but a harmless request 502 (\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other 503 errors should be according to the standards, whatever they are. When 504 an error is returned by the low-level driver, the \UCD\ tries whenever 505 possible to return the error code to the calling program. (We may decide 506 to sanitize the return value in $cdrom_ioctl()$ though, in order to 507 guarantee a uniform interface to the audio-player software.) 508 509 \subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\ 510 cmd, unsigned\ long\ arg)$} 511 512 Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is, 513 they are introduced to service some capabilities of certain drives. In 514 fact, there are 6 different $ioctl$s for reading data, either in some 515 particular kind of format, or audio data. Not many drives support 516 reading audio tracks as data, I believe this is because of protection 517 of copyrights of artists. Moreover, I think that if audio-tracks are 518 supported, it should be done through the VFS and not via $ioctl$s. A 519 problem here could be the fact that audio-frames are 2352 bytes long, 520 so either the audio-file-system should ask for 75264 bytes at once 521 (the least common multiple of 512 and 2352), or the drivers should 522 bend their backs to cope with this incoherence (to which I would be 523 opposed). Furthermore, it is very difficult for the hardware to find 524 the exact frame boundaries, since there are no synchronization headers 525 in audio frames. Once these issues are resolved, this code should be 526 standardized in \cdromc. 527 528 Because there are so many $ioctl$s that seem to be introduced to 529 satisfy certain drivers,\footnote{Is there software around that 530 actually uses these? I'd be interested!} any `non-standard' $ioctl$s 531 are routed through the call $dev_ioctl()$. In principle, `private' 532 $ioctl$s should be numbered after the device's major number, and not 533 the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the 534 non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2, 535 CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK, 536 CDROMPLAY\-BLK and CDROM\-READALL}. 537 538 539 \subsection{\cdrom\ capabilities} 540 \label{capability} 541 542 Instead of just implementing some $ioctl$ calls, the interface in 543 \cdromc\ supplies the possibility to indicate the {\em capabilities\/} 544 of a \cdrom\ drive. This can be done by ORing any number of 545 capability-constants that are defined in \cdromh\ at the registration 546 phase. Currently, the capabilities are any of: 547 $$ 548 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 549 CDC_CLOSE_TRAY& can close tray by software control\cr 550 CDC_OPEN_TRAY& can open tray\cr 551 CDC_LOCK& can lock and unlock the door\cr 552 CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr 553 CDC_SELECT_DISC& drive is juke-box\cr 554 CDC_MULTI_SESSION& can read sessions $>\rm1$\cr 555 CDC_MCN& can read Media Catalog Number\cr 556 CDC_MEDIA_CHANGED& can report if disc has changed\cr 557 CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr 558 CDC_RESET& hard reset device\cr 559 CDC_IOCTLS& driver has non-standard ioctls\cr 560 CDC_DRIVE_STATUS& driver implements drive status\cr 561 } 562 $$ 563 The capability flag is declared $const$, to prevent drivers from 564 accidentally tampering with the contents. The capability fags actually 565 inform \cdromc\ of what the driver can do. If the drive found 566 by the driver does not have the capability, is can be masked out by 567 the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\ 568 driver has implemented the code for loading and ejecting \cdrom's, and 569 hence its corresponding flags in $capability$ will be set. But a SCSI 570 \cdrom\ drive might be a caddy system, which can't load the tray, and 571 hence for this drive the $cdrom_device_info$ struct will have set 572 the $CDC_CLOSE_TRAY$ bit in $mask$. 573 574 In the file \cdromc\ you will encounter many constructions of the type 575 $$\it 576 if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 577 \mathrel{\&} CDC_<capability>) \ldots 578 $$ 579 There is no $ioctl$ to set the mask\dots The reason is that 580 I think it is better to control the {\em behavior\/} rather than the 581 {\em capabilities}. 582 583 \subsection{Options} 584 585 A final flag register controls the {\em behavior\/} of the \cdrom\ 586 drives, in order to satisfy different users' wishes, hopefully 587 independently of the ideas of the respective author who happened to 588 have made the drive's support available to the \linux\ community. The 589 current behavior options are: 590 $$ 591 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 592 CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr 593 CDO_AUTO_EJECT& try to open tray on last device $close()$\cr 594 CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate 595 purpose for $open()$\cr 596 CDO_LOCK& try to lock door if device is opened\cr 597 CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr 598 } 599 $$ 600 601 The initial value of this register is $CDO_AUTO_CLOSE \mathrel| 602 CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user 603 interface and software standards. Before you protest, there are two 604 new $ioctl$s implemented in \cdromc, that allow you to control the 605 behavior by software. These are: 606 $$ 607 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 608 CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr 609 CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr 610 } 611 $$ 612 One option needs some more explanation: $CDO_USE_FFLAGS$. In the next 613 newsection we explain what the need for this option is. 614 615 A software package {\tt setcd}, available from the Debian distribution 616 and {\tt sunsite.unc.edu}, allows user level control of these flags. 617 618 \newsection{The need to know the purpose of opening the \cdrom\ device} 619 620 Traditionally, Unix devices can be used in two different `modes', 621 either by reading/writing to the device file, or by issuing 622 controlling commands to the device, by the device's $ioctl()$ 623 call. The problem with \cdrom\ drives, is that they can be used for 624 two entirely different purposes. One is to mount removable 625 file systems, \cdrom s, the other is to play audio CD's. Audio commands 626 are implemented entirely through $ioctl$s, presumably because the 627 first implementation (SUN?) has been such. In principle there is 628 nothing wrong with this, but a good control of the `CD player' demands 629 that the device can {\em always\/} be opened in order to give the 630 $ioctl$ commands, regardless of the state the drive is in. 631 632 On the other hand, when used as a removable-media disc drive (what the 633 original purpose of \cdrom s is) we would like to make sure that the 634 disc drive is ready for operation upon opening the device. In the old 635 scheme, some \cdrom\ drivers don't do any integrity checking, resulting 636 in a number of i/o errors reported by the VFS to the kernel when an 637 attempt for mounting a \cdrom\ on an empty drive occurs. This is not a 638 particularly elegant way to find out that there is no \cdrom\ inserted; 639 it more-or-less looks like the old IBM-PC trying to read an empty floppy 640 drive for a couple of seconds, after which the system complains it 641 can't read from it. Nowadays we can {\em sense\/} the existence of a 642 removable medium in a drive, and we believe we should exploit that 643 fact. An integrity check on opening of the device, that verifies the 644 availability of a \cdrom\ and its correct type (data), would be 645 desirable. 646 647 These two ways of using a \cdrom\ drive, principally for data and 648 secondarily for playing audio discs, have different demands for the 649 behavior of the $open()$ call. Audio use simply wants to open the 650 device in order to get a file handle which is needed for issuing 651 $ioctl$ commands, while data use wants to open for correct and 652 reliable data transfer. The only way user programs can indicate what 653 their {\em purpose\/} of opening the device is, is through the $flags$ 654 parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't 655 implemented (some drivers implement checking for write-related flags, 656 but this is not strictly necessary if the device file has correct 657 permission flags). Most option flags simply don't make sense to 658 \cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and 659 $O_SYNC$ have no meaning to a \cdrom. 660 661 We therefore propose to use the flag $O_NONBLOCK$ to indicate 662 that the device is opened just for issuing $ioctl$ 663 commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and 664 subsequent calls to the device don't cause the calling process to 665 wait. We could interpret this as ``don't wait until someone has 666 inserted some valid data-\cdrom.'' Thus, our proposal of the 667 implementation for the $open()$ call for \cdrom s is: 668 \begin{itemize} 669 \item If no other flags are set than $O_RDONLY$, the device is opened 670 for data transfer, and the return value will be 0 only upon successful 671 initialization of the transfer. The call may even induce some actions 672 on the \cdrom, such as closing the tray. 673 \item If the option flag $O_NONBLOCK$ is set, opening will always be 674 successful, unless the whole device doesn't exist. The drive will take 675 no actions whatsoever. 676 \end{itemize} 677 678 \subsection{And what about standards?} 679 680 You might hesitate to accept this proposal as it comes from the 681 \linux\ community, and not from some standardizing institute. What 682 about SUN, SGI, HP and all those other Unix and hardware vendors? 683 Well, these companies are in the lucky position that they generally 684 control both the hardware and software of their supported products, 685 and are large enough to set their own standard. They do not have to 686 deal with a dozen or more different, competing hardware 687 configurations.\footnote{Incidentally, I think that SUN's approach to 688 mounting \cdrom s is very good in origin: under Solaris a 689 volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt 690 {/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this 691 further and have {\em every\/} \cdrom\ on the local area network be 692 mounted at the similar location, \ie, no matter in which particular 693 machine you insert a \cdrom, it will always appear at the same 694 position in the directory tree, on every system. When I wanted to 695 implement such a user-program for \linux, I came across the 696 differences in behavior of the various drivers, and the need for an 697 $ioctl$ informing about media changes.} 698 699 We believe that using $O_NONBLOCK$ to indicate that a device is being opened 700 for $ioctl$ commands only can be easily introduced in the \linux\ 701 community. All the CD-player authors will have to be informed, we can 702 even send in our own patches to the programs. The use of $O_NONBLOCK$ 703 has most likely no influence on the behavior of the CD-players on 704 other operating systems than \linux. Finally, a user can always revert 705 to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, 706 CDO_USE_FFLAGS)$. 707 708 \subsection{The preferred strategy of $open()$} 709 710 The routines in \cdromc\ are designed in such a way that run-time 711 configuration of the behavior of \cdrom\ devices (of {\em any\/} type) 712 can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various 713 modes of operation can be set: 714 \begin{description} 715 \item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This 716 is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the 717 future.) If the device is not yet opened by any other process, and if 718 the device is being opened for data ($O_NONBLOCK$ is not set) and the 719 tray is found to be open, an attempt to close the tray is made. Then, 720 it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is 721 set, that it contains tracks of type `data mode 1.' Only if all tests 722 are passed is the return value zero. The door is locked to prevent file 723 system corruption. If the drive is opened for audio ($O_NONBLOCK$ is 724 set), no actions are taken and a value of 0 will be returned. 725 \item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This 726 mimics the behavior of the current sbpcd-driver. The option flags are 727 ignored, the tray is closed on the first open, if necessary. Similarly, 728 the tray is opened on the last release, \ie, if a \cdrom\ is unmounted, 729 it is automatically ejected, such that the user can replace it. 730 \end{description} 731 We hope that these option can convince everybody (both driver 732 maintainers and user program developers) to adopt the new \cdrom\ 733 driver scheme and option flag interpretation. 734 735 \newsection{Description of routines in \cdromc} 736 737 Only a few routines in \cdromc\ are exported to the drivers. In this 738 new section we will discuss these, as well as the functions that `take 739 over' the \cdrom\ interface to the kernel. The header file belonging 740 to \cdromc\ is called \cdromh. Formerly, some of the contents of this 741 file were placed in the file {\tt {ucdrom.h}}, but this file has now been 742 merged back into \cdromh. 743 744 \subsection{$Struct\ file_operations\ cdrom_fops$} 745 746 The contents of this structure were described in section~\ref{cdrom.c}. 747 A pointer to this structure is assigned to the $fops$ field 748 of the $struct gendisk$. 749 750 \subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$} 751 752 This function is used in about the same way one registers $cdrom_fops$ 753 with the kernel, the device operations and information structures, 754 as described in section~\ref{cdrom.c}, should be registered with the 755 \UCD: 756 $$ 757 register_cdrom(\&<device>_info)); 758 $$ 759 This function returns zero upon success, and non-zero upon 760 failure. The structure $<device>_info$ should have a pointer to the 761 driver's $<device>_dops$, as in 762 $$ 763 \vbox{\halign{&$#$\hfil\cr 764 struct\ &cdrom_device_info\ <device>_info = \{\cr 765 & <device>_dops;\cr 766 &\ldots\cr 767 \}\cr 768 }}$$ 769 Note that a driver must have one static structure, $<device>_dops$, while 770 it may have as many structures $<device>_info$ as there are minor devices 771 active. $Register_cdrom()$ builds a linked list from these. 772 773 \subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$} 774 775 Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes 776 the minor device from the list. If it was the last registered minor for 777 the low-level driver, this disconnects the registered device-operation 778 routines from the \cdrom\ interface. This function returns zero upon 779 success, and non-zero upon failure. 780 781 \subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$} 782 783 This function is not called directly by the low-level drivers, it is 784 listed in the standard $cdrom_fops$. If the VFS opens a file, this 785 function becomes active. A strategy is implemented in this routine, 786 taking care of all capabilities and options that are set in the 787 $cdrom_device_ops$ connected to the device. Then, the program flow is 788 transferred to the device_dependent $open()$ call. 789 790 \subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file 791 *fp)$} 792 793 This function implements the reverse-logic of $cdrom_open()$, and then 794 calls the device-dependent $release()$ routine. When the use-count has 795 reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$ 796 and $invalidate_buffers(dev)$. 797 798 799 \subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp, 800 unsigned\ int\ cmd, unsigned\ long\ arg)$} 801 \label{cdrom-ioctl} 802 803 This function handles all the standard $ioctl$ requests for \cdrom\ 804 devices in a uniform way. The different calls fall into three 805 categories: $ioctl$s that can be directly implemented by device 806 operations, ones that are routed through the call $audio_ioctl()$, and 807 the remaining ones, that are presumable device-dependent. Generally, a 808 negative return value indicates an error. 809 810 \subsubsection{Directly implemented $ioctl$s} 811 \label{ioctl-direct} 812 813 The following `old' \cdrom-$ioctl$s are implemented by directly 814 calling device-operations in $cdrom_device_ops$, if implemented and 815 not masked: 816 \begin{description} 817 \item[CDROMMULTISESSION] Requests the last session on a \cdrom. 818 \item[CDROMEJECT] Open tray. 819 \item[CDROMCLOSETRAY] Close tray. 820 \item[CDROMEJECT_SW] If $arg\not=0$, set behavior to auto-close (close 821 tray on first open) and auto-eject (eject on last release), otherwise 822 set behavior to non-moving on $open()$ and $release()$ calls. 823 \item[CDROM_GET_MCN] Get the Media Catalog Number from a CD. 824 \end{description} 825 826 \subsubsection{$Ioctl$s routed through $audio_ioctl()$} 827 \label{ioctl-audio} 828 829 The following set of $ioctl$s are all implemented through a call to 830 the $cdrom_fops$ function $audio_ioctl()$. Memory checks and 831 allocation are performed in $cdrom_ioctl()$, and also sanitization of 832 address format ($CDROM_LBA$/$CDROM_MSF$) is done. 833 \begin{description} 834 \item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\ 835 cdrom_subchnl *{}$. 836 \item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type 837 $struct\ cdrom_tochdr *{}$. 838 \item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and 839 specified by $arg$ of type $struct\ cdrom_tocentry *{}$. 840 \item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second, 841 Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$. 842 \item[CDROMPLAYTRKIND] Play audio fragment in track-index format 843 delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$. 844 \item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\ 845 cdrom_volctrl *{}$. 846 \item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\ 847 cdrom_volctrl *{}$. 848 \item[CDROMSTART] Spin up disc. 849 \item[CDROMSTOP] Stop playback of audio fragment. 850 \item[CDROMPAUSE] Pause playback of audio fragment. 851 \item[CDROMRESUME] Resume playing. 852 \end{description} 853 854 \subsubsection{New $ioctl$s in \cdromc} 855 856 The following $ioctl$s have been introduced to allow user programs to 857 control the behavior of individual \cdrom\ devices. New $ioctl$ 858 commands can be identified by the underscores in their names. 859 \begin{description} 860 \item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the 861 option flag register after modification. Use $arg = \rm0$ for reading 862 the current flags. 863 \item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns 864 the option flag register after modification. 865 \item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as 866 by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or 867 150\,kB/sec file system data). The value 0 means `auto-select', \ie, 868 play audio discs at real time and data discs at maximum speed. The value 869 $arg$ is checked against the maximum head rate of the drive found in the 870 $cdrom_dops$. 871 \item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box. 872 First disc is numbered 0. The number $arg$ is checked against the 873 maximum number of discs in the juke-box found in the $cdrom_dops$. 874 \item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since 875 the last call. Note that calls to $cdrom_media_changed$ by the VFS 876 are treated by an independent queue, so both mechanisms will detect 877 a media change once. For juke-boxes, an extra argument $arg$ 878 specifies the slot for which the information is given. The special 879 value $CDSL_CURRENT$ requests that information about the currently 880 selected slot be returned. 881 \item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to 882 $drive_status()$. Return values are defined in section~\ref{drive 883 status}. Note that this call doesn't return information on the 884 current playing activity of the drive; this can be polled through an 885 $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument 886 $arg$ specifies the slot for which (possibly limited) information is 887 given. The special value $CDSL_CURRENT$ requests that information 888 about the currently selected slot be returned. 889 \item[CDROM_DISC_STATUS] Returns the type of the disc currently in the 890 drive. It should be viewed as a complement to $CDROM_DRIVE_STATUS$. 891 This $ioctl$ can provide \emph {some} information about the current 892 disc that is inserted in the drive. This functionality used to be 893 implemented in the low level drivers, but is now carried out 894 entirely in \UCD. 895 896 The history of development of the CD's use as a carrier medium for 897 various digital information has lead to many different disc types. 898 This $ioctl$ is useful only in the case that CDs have \emph {only 899 one} type of data on them. While this is often the case, it is 900 also very common for CDs to have some tracks with data, and some 901 tracks with audio. Because this is an existing interface, rather 902 than fixing this interface by changing the assumptions it was made 903 under, thereby breaking all user applications that use this 904 function, the \UCD\ implements this $ioctl$ as follows: If the CD in 905 question has audio tracks on it, and it has absolutely no CD-I, XA, 906 or data tracks on it, it will be reported as $CDS_AUDIO$. If it has 907 both audio and data tracks, it will return $CDS_MIXED$. If there 908 are no audio tracks on the disc, and if the CD in question has any 909 CD-I tracks on it, it will be reported as $CDS_XA_2_2$. Failing 910 that, if the CD in question has any XA tracks on it, it will be 911 reported as $CDS_XA_2_1$. Finally, if the CD in question has any 912 data tracks on it, it will be reported as a data CD ($CDS_DATA_1$). 913 914 This $ioctl$ can return: 915 $$ 916 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 917 CDS_NO_INFO& no information available\cr 918 CDS_NO_DISC& no disc is inserted, or tray is opened\cr 919 CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr 920 CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr 921 CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr 922 CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324 user bytes)\cr 923 CDS_MIXED& mixed audio/data disc\cr 924 } 925 $$ 926 For some information concerning frame layout of the various disc 927 types, see a recent version of \cdromh. 928 929 \item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a 930 juke-box. 931 \item[CDROMRESET] Reset the drive. 932 \item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the 933 drive. Refer to section \ref{capability} for more information on 934 these flags. 935 \item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$ 936 unlocks the door, any other value locks it. 937 \item[CDROM_DEBUG] Turns on debugging info. Only root is allowed 938 to do this. Same semantics as CDROM_LOCKDOOR. 939 \end{description} 940 941 \subsubsection{Device dependent $ioctl$s} 942 943 Finally, all other $ioctl$s are passed to the function $dev_ioctl()$, 944 if implemented. No memory allocation or verification is carried out. 945 946 \newsection{How to update your driver} 947 948 \begin{enumerate} 949 \item Make a backup of your current driver. 950 \item Get hold of the files \cdromc\ and \cdromh, they should be in 951 the directory tree that came with this documentation. 952 \item Make sure you include \cdromh. 953 \item Change the 3rd argument of $register_blkdev$ from 954 $\&<your-drive>_fops$ to $\&cdrom_fops$. 955 \item Just after that line, add the following to register with the \UCD: 956 $$register_cdrom(\&<your-drive>_info);$$ 957 Similarly, add a call to $unregister_cdrom()$ at the appropriate place. 958 \item Copy an example of the device-operations $struct$ to your 959 source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all 960 entries to names corresponding to your driver, or names you just 961 happen to like. If your driver doesn't support a certain function, 962 make the entry $NULL$. At the entry $capability$ you should list all 963 capabilities your driver currently supports. If your driver 964 has a capability that is not listed, please send me a message. 965 \item Copy the $cdrom_device_info$ declaration from the same example 966 driver, and modify the entries according to your needs. If your 967 driver dynamically determines the capabilities of the hardware, this 968 structure should also be declared dynamically. 969 \item Implement all functions in your $<device>_dops$ structure, 970 according to prototypes listed in \cdromh, and specifications given 971 in section~\ref{cdrom.c}. Most likely you have already implemented 972 the code in a large part, and you will almost certainly need to adapt the 973 prototype and return values. 974 \item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and 975 change the prototype a little. Remove entries listed in the first 976 part in section~\ref{cdrom-ioctl}, if your code was OK, these are 977 just calls to the routines you adapted in the previous step. 978 \item You may remove all remaining memory checking code in the 979 $audio_ioctl()$ function that deals with audio commands (these are 980 listed in the second part of section~\ref{cdrom-ioctl}). There is no 981 need for memory allocation either, so most $case$s in the $switch$ 982 statement look similar to: 983 $$ 984 case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\ 985 cdrom_tocentry *{})\ arg\bigr); 986 $$ 987 \item All remaining $ioctl$ cases must be moved to a separate 988 function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that 989 memory checking and allocation must be kept in this code! 990 \item Change the prototypes of $<device>_open()$ and 991 $<device>_release()$, and remove any strategic code (\ie, tray 992 movement, door locking, etc.). 993 \item Try to recompile the drivers. We advise you to use modules, both 994 for {\tt {cdrom.o}} and your driver, as debugging is much easier this 995 way. 996 \end{enumerate} 997 998 \newsection{Thanks} 999 1000 Thanks to all the people involved. First, Erik Andersen, who has 1001 taken over the torch in maintaining \cdromc\ and integrating much 1002 \cdrom-related code in the 2.1-kernel. Thanks to Scott Snyder and 1003 Gerd Knorr, who were the first to implement this interface for SCSI 1004 and IDE-CD drivers and added many ideas for extension of the data 1005 structures relative to kernel~2.0. Further thanks to Heiko Ei{\sz}feldt, 1006 Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew 1007 Kroll, the \linux\ \cdrom\ device driver developers who were kind 1008 enough to give suggestions and criticisms during the writing. Finally 1009 of course, I want to thank Linus Torvalds for making this possible in 1010 the first place. 1011 1012 \vfill 1013 $ \version\ $ 1014 \eject 1015 \end{document}