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Root/Documentation/cdrom/cdrom-standard.tex

 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}, $_dops$. 158 These operations are different from the classical block-device file 159 operations, $_fops$. 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 $$register_cdrom(struct\ cdrom_device_info * _info) 214$$ 215 The device information structure, $_info$, contains all the 216 information needed for the kernel to interface with the low-level 217 \cdrom\ device driver. One of the most important entries in this 218 structure is a pointer to the $cdrom_device_ops$ structure of the 219 low-level driver. 220 221 The device operations structure, $cdrom_device_ops$, contains a list 222 of pointers to the functions which are implemented in the low-level 223 device driver. When \cdromc\ accesses a \cdrom\ device, it does it 224 through the functions in this structure. It is impossible to know all 225 the capabilities of future \cdrom\ drives, so it is expected that this 226 list may need to be expanded from time to time as new technologies are 227 developed. For example, CD-R and CD-R/W drives are beginning to become 228 popular, and support will soon need to be added for them. For now, the 229 current $struct$ is: 230 231 \halign{#\ \hfil&#\ \hfil&\hbox to 10em{#\hss}& 232 /* \rm# */\hfil\cr 233 struct& cdrom_device_ops\ \{ \hidewidth\cr 234 &int& (* open)(struct\ cdrom_device_info *, int)\cr 235 &void& (* release)(struct\ cdrom_device_info *);\cr 236 &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr 237 &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 238 &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr 239 &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr 240 &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr 241 &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr 242 &int& (* get_last_session) (struct\ cdrom_device_info *, 243 struct\ cdrom_multisession *{});\cr 244 &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr 245 &int& (* reset)(struct\ cdrom_device_info *);\cr 246 &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 247 void *{});\cr 248 &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 249 unsigned\ long);\cr 250 \noalign{\medskip} 251 &const\ int& capability;& capability flags \cr 252 &int& n_minors;& number of active minor devices \cr 253 \};\cr 254 } 255 256 When a low-level device driver implements one of these capabilities, 257 it should add a function pointer to this $struct$. When a particular 258 function is not implemented, however, this $struct$ should contain a 259 NULL instead. The $capability$ flags specify the capabilities of the 260 \cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive 261 is registered with the \UCD. The value $n_minors$ should be a positive 262 value indicating the number of minor devices that are supported by 263 the low-level device driver, normally~1. Although these two variables 264 are informative' rather than operational,' they are included in 265 $cdrom_device_ops$ because they describe the capability of the {\em 266 driver\/} rather than the {\em drive}. Nomenclature has always been 267 difficult in computer programming. 268 269 Note that most functions have fewer parameters than their 270 $blkdev_fops$ counterparts. This is because very little of the 271 information in the structures $inode$ and $file$ is used. For most 272 drivers, the main parameter is the $struct$ $cdrom_device_info$, from 273 which the major and minor number can be extracted. (Most low-level 274 \cdrom\ drivers don't even look at the major and minor number though, 275 since many of them only support one device.) This will be available 276 through $dev$ in $cdrom_device_info$ described below. 277 278 The drive-specific, minor-like information that is registered with 279 \cdromc, currently contains the following fields: 280 281 \halign{#\ \hfil&#\ \hfil&\hbox to 10em{#\hss}& 282 /* \rm# */\hfil\cr 283 struct& cdrom_device_info\ \{ \hidewidth\cr 284 & struct\ cdrom_device_ops *& ops;& device operations for this major\cr 285 & struct\ cdrom_device_info *& next;& next device_info for this major\cr 286 & void *& handle;& driver-dependent data\cr 287 \noalign{\medskip} 288 & kdev_t& dev;& device number (incorporates minor)\cr 289 & int& mask;& mask of capability: disables them \cr 290 & int& speed;& maximum speed for reading data \cr 291 & int& capacity;& number of discs in a jukebox \cr 292 \noalign{\medskip} 293 &int& options : 30;& options flags \cr 294 &unsigned& mc_flags : 2;& media-change buffer flags \cr 295 & int& use_count;& number of times device is opened\cr 296 & char& name[20];& name of the device type\cr 297 \}\cr 298 } 299 Using this $struct$, a linked list of the registered minor devices is 300 built, using the $next$ field. The device number, the device operations 301 struct and specifications of properties of the drive are stored in this 302 structure. 303 304 The $mask$ flags can be used to mask out some of the capabilities listed 305 in $ops\to capability$, if a specific drive doesn't support a feature 306 of the driver. The value $speed$ specifies the maximum head-rate of the 307 drive, measured in units of normal audio speed (176\,kB/sec raw data or 308 150\,kB/sec file system data). The value $n_discs$ should reflect the 309 number of discs the drive can hold simultaneously, if it is designed 310 as a juke-box, or otherwise~1. The parameters are declared $const$ 311 because they describe properties of the drive, which don't change after 312 registration. 313 314 A few registers contain variables local to the \cdrom\ drive. The 315 flags $options$ are used to specify how the general \cdrom\ routines 316 should behave. These various flags registers should provide enough 317 flexibility to adapt to the different users' wishes (and {\em not\/} the 318 arbitrary' wishes of the author of the low-level device driver, as is 319 the case in the old scheme). The register $mc_flags$ is used to buffer 320 the information from $media_changed()$ to two separate queues. Other 321 data that is specific to a minor drive, can be accessed through $handle$, 322 which can point to a data structure specific to the low-level driver. 323 The fields $use_count$, $next$, $options$ and $mc_flags$ need not be 324 initialized. 325 326 The intermediate software layer that \cdromc\ forms will perform some 327 additional bookkeeping. The use count of the device (the number of 328 processes that have the device opened) is registered in $use_count$. The 329 function $cdrom_ioctl()$ will verify the appropriate user-memory regions 330 for read and write, and in case a location on the CD is transferred, 331 it will sanitize' the format by making requests to the low-level 332 drivers in a standard format, and translating all formats between the 333 user-software and low level drivers. This relieves much of the drivers' 334 memory checking and format checking and translation. Also, the necessary 335 structures will be declared on the program stack. 336 337 The implementation of the functions should be as defined in the 338 following sections. Two functions {\em must\/} be implemented, namely 339 $open()$ and $release()$. Other functions may be omitted, their 340 corresponding capability flags will be cleared upon registration. 341 Generally, a function returns zero on success and negative on error. A 342 function call should return only after the command has completed, but of 343 course waiting for the device should not use processor time. 344 345 \subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$} 346 347 $Open()$ should try to open the device for a specific $purpose$, which 348 can be either: 349 \begin{itemize} 350 \item[0] Open for reading data, as done by {\tt {mount()}} (2), or the 351 user commands {\tt {dd}} or {\tt {cat}}. 352 \item[1] Open for $ioctl$ commands, as done by audio-CD playing 353 programs. 354 \end{itemize} 355 Notice that any strategic code (closing tray upon $open()$, etc.)\ is 356 done by the calling routine in \cdromc, so the low-level routine 357 should only be concerned with proper initialization, such as spinning 358 up the disc, etc. % and device-use count 359 360 361 \subsection{$Void\ release(struct\ cdrom_device_info * cdi)$} 362 363 364 Device-specific actions should be taken such as spinning down the device. 365 However, strategic actions such as ejection of the tray, or unlocking 366 the door, should be left over to the general routine $cdrom_release()$. 367 This is the only function returning type $void$. 368 369 \subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$} 370 \label{drive status} 371 372 The function $drive_status$, if implemented, should provide 373 information on the status of the drive (not the status of the disc, 374 which may or may not be in the drive). If the drive is not a changer, 375 $slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 376 377 \halign{#\ \hfil&/* \rm# */\hfil\cr 378 CDS_NO_INFO& no information available\cr 379 CDS_NO_DISC& no disc is inserted, tray is closed\cr 380 CDS_TRAY_OPEN& tray is opened\cr 381 CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr 382 CDS_DISC_OK& a disc is loaded and everything is fine\cr 383 } 384 385 386 \subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$} 387 388 This function is very similar to the original function in $struct\ 389 file_operations$. It returns 1 if the medium of the device $cdi\to 390 dev$ has changed since the last call, and 0 otherwise. The parameter 391 $disc_nr$ identifies a specific slot in a juke-box, it should be 392 ignored for single-disc drives. Note that by re-routing' this 393 function through $cdrom_media_changed()$, we can implement separate 394 queues for the VFS and a new $ioctl()$ function that can report device 395 changes to software (\eg, an auto-mounting daemon). 396 397 \subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$} 398 399 This function, if implemented, should control the tray movement. (No 400 other function should control this.) The parameter $position$ controls 401 the desired direction of movement: 402 \begin{itemize} 403 \item[0] Close tray 404 \item[1] Open tray 405 \end{itemize} 406 This function returns 0 upon success, and a non-zero value upon 407 error. Note that if the tray is already in the desired position, no 408 action need be taken, and the return value should be 0. 409 410 \subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$} 411 412 This function (and no other code) controls locking of the door, if the 413 drive allows this. The value of $lock$ controls the desired locking 414 state: 415 \begin{itemize} 416 \item[0] Unlock door, manual opening is allowed 417 \item[1] Lock door, tray cannot be ejected manually 418 \end{itemize} 419 This function returns 0 upon success, and a non-zero value upon 420 error. Note that if the door is already in the requested state, no 421 action need be taken, and the return value should be 0. 422 423 \subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$} 424 425 Some \cdrom\ drives are capable of changing their head-speed. There 426 are several reasons for changing the speed of a \cdrom\ drive. Badly 427 pressed \cdrom s may benefit from less-than-maximum head rate. Modern 428 \cdrom\ drives can obtain very high head rates (up to $24\times$ is 429 common). It has been reported that these drives can make reading 430 errors at these high speeds, reducing the speed can prevent data loss 431 in these circumstances. Finally, some of these drives can 432 make an annoyingly loud noise, which a lower speed may reduce. %Finally, 433 %although the audio-low-pass filters probably aren't designed for it, 434 %more than real-time playback of audio might be used for high-speed 435 %copying of audio tracks. 436 437 This function specifies the speed at which data is read or audio is 438 played back. The value of $speed$ specifies the head-speed of the 439 drive, measured in units of standard cdrom speed (176\,kB/sec raw data 440 or 150\,kB/sec file system data). So to request that a \cdrom\ drive 441 operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$ 442 with $speed=2$. The special value 0' means auto-selection', \ie, 443 maximum data-rate or real-time audio rate. If the drive doesn't have 444 this auto-selection' capability, the decision should be made on the 445 current disc loaded and the return value should be positive. A negative 446 return value indicates an error. 447 448 \subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$} 449 450 If the drive can store multiple discs (a juke-box) this function 451 will perform disc selection. It should return the number of the 452 selected disc on success, a negative value on error. Currently, only 453 the ide-cd driver supports this functionality. 454 455 \subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\ 456 cdrom_multisession * ms_info)$} 457 458 This function should implement the old corresponding $ioctl()$. For 459 device $cdi\to dev$, the start of the last session of the current disc 460 should be returned in the pointer argument $ms_info$. Note that 461 routines in \cdromc\ have sanitized this argument: its requested 462 format will {\em always\/} be of the type $CDROM_LBA$ (linear block 463 addressing mode), whatever the calling software requested. But 464 sanitization goes even further: the low-level implementation may 465 return the requested information in $CDROM_MSF$ format if it wishes so 466 (setting the $ms_info\rightarrow addr_format$ field appropriately, of 467 course) and the routines in \cdromc\ will make the transformation if 468 necessary. The return value is 0 upon success. 469 470 \subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\ 471 cdrom_mcn * mcn)$} 472 473 Some discs carry a Media Catalog Number' (MCN), also called 474 Universal Product Code' (UPC). This number should reflect the number 475 that is generally found in the bar-code on the product. Unfortunately, 476 the few discs that carry such a number on the disc don't even use the 477 same format. The return argument to this function is a pointer to a 478 pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is 479 expected as a 13-character string, terminated by a null-character. 480 481 \subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$} 482 483 This call should perform a hard-reset on the drive (although in 484 circumstances that a hard-reset is necessary, a drive may very well not 485 listen to commands anymore). Preferably, control is returned to the 486 caller only after the drive has finished resetting. If the drive is no 487 longer listening, it may be wise for the underlying low-level cdrom 488 driver to time out. 489 490 \subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\ 491 int\ cmd, void * arg)$} 492 493 Some of the \cdrom-$ioctl$s defined in \cdromh\ can be 494 implemented by the routines described above, and hence the function 495 $cdrom_ioctl$ will use those. However, most $ioctl$s deal with 496 audio-control. We have decided to leave these to be accessed through a 497 single function, repeating the arguments $cmd$ and $arg$. Note that 498 the latter is of type $void*{}$, rather than $unsigned\ long\ 499 int$. The routine $cdrom_ioctl()$ does do some useful things, 500 though. It sanitizes the address format type to $CDROM_MSF$ (Minutes, 501 Seconds, Frames) for all audio calls. It also verifies the memory 502 location of $arg$, and reserves stack-memory for the argument. This 503 makes implementation of the $audio_ioctl()$ much simpler than in the 504 old driver scheme. For example, you may look up the function 505 $cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with 506 this documentation. 507 508 An unimplemented ioctl should return $-ENOSYS$, but a harmless request 509 (\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other 510 errors should be according to the standards, whatever they are. When 511 an error is returned by the low-level driver, the \UCD\ tries whenever 512 possible to return the error code to the calling program. (We may decide 513 to sanitize the return value in $cdrom_ioctl()$ though, in order to 514 guarantee a uniform interface to the audio-player software.) 515 516 \subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\ 517 cmd, unsigned\ long\ arg)$} 518 519 Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is, 520 they are introduced to service some capabilities of certain drives. In 521 fact, there are 6 different $ioctl$s for reading data, either in some 522 particular kind of format, or audio data. Not many drives support 523 reading audio tracks as data, I believe this is because of protection 524 of copyrights of artists. Moreover, I think that if audio-tracks are 525 supported, it should be done through the VFS and not via $ioctl$s. A 526 problem here could be the fact that audio-frames are 2352 bytes long, 527 so either the audio-file-system should ask for 75264 bytes at once 528 (the least common multiple of 512 and 2352), or the drivers should 529 bend their backs to cope with this incoherence (to which I would be 530 opposed). Furthermore, it is very difficult for the hardware to find 531 the exact frame boundaries, since there are no synchronization headers 532 in audio frames. Once these issues are resolved, this code should be 533 standardized in \cdromc. 534 535 Because there are so many $ioctl$s that seem to be introduced to 536 satisfy certain drivers,\footnote{Is there software around that 537 actually uses these? I'd be interested!} any non-standard' $ioctl$s 538 are routed through the call $dev_ioctl()$. In principle, private' 539 $ioctl$s should be numbered after the device's major number, and not 540 the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the 541 non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2, 542 CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK, 543 CDROMPLAY\-BLK and CDROM\-READALL}. 544 545 546 \subsection{\cdrom\ capabilities} 547 \label{capability} 548 549 Instead of just implementing some $ioctl$ calls, the interface in 550 \cdromc\ supplies the possibility to indicate the {\em capabilities\/} 551 of a \cdrom\ drive. This can be done by ORing any number of 552 capability-constants that are defined in \cdromh\ at the registration 553 phase. Currently, the capabilities are any of: 554 555 \halign{#\ \hfil&/* \rm# */\hfil\cr 556 CDC_CLOSE_TRAY& can close tray by software control\cr 557 CDC_OPEN_TRAY& can open tray\cr 558 CDC_LOCK& can lock and unlock the door\cr 559 CDC_SELECT_SPEED& can select speed, in units of \sim150\,kB/s\cr 560 CDC_SELECT_DISC& drive is juke-box\cr 561 CDC_MULTI_SESSION& can read sessions >\rm1\cr 562 CDC_MCN& can read Media Catalog Number\cr 563 CDC_MEDIA_CHANGED& can report if disc has changed\cr 564 CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr 565 CDC_RESET& hard reset device\cr 566 CDC_IOCTLS& driver has non-standard ioctls\cr 567 CDC_DRIVE_STATUS& driver implements drive status\cr 568 } 569 570 The capability flag is declared $const$, to prevent drivers from 571 accidentally tampering with the contents. The capability fags actually 572 inform \cdromc\ of what the driver can do. If the drive found 573 by the driver does not have the capability, is can be masked out by 574 the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\ 575 driver has implemented the code for loading and ejecting \cdrom's, and 576 hence its corresponding flags in $capability$ will be set. But a SCSI 577 \cdrom\ drive might be a caddy system, which can't load the tray, and 578 hence for this drive the $cdrom_device_info$ struct will have set 579 the $CDC_CLOSE_TRAY$ bit in $mask$. 580 581 In the file \cdromc\ you will encounter many constructions of the type 582 $$\it 583 if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 584 \mathrel{\&} CDC_) \ldots 585$$ 586 There is no $ioctl$ to set the mask\dots The reason is that 587 I think it is better to control the {\em behavior\/} rather than the 588 {\em capabilities}. 589 590 \subsection{Options} 591 592 A final flag register controls the {\em behavior\/} of the \cdrom\ 593 drives, in order to satisfy different users' wishes, hopefully 594 independently of the ideas of the respective author who happened to 595 have made the drive's support available to the \linux\ community. The 596 current behavior options are: 597 598 \halign{#\ \hfil&/* \rm# */\hfil\cr 599 CDO_AUTO_CLOSE& try to close tray upon device open()\cr 600 CDO_AUTO_EJECT& try to open tray on last device close()\cr 601 CDO_USE_FFLAGS& use file_pointer\rightarrow f_flags to indicate 602 purpose for open()\cr 603 CDO_LOCK& try to lock door if device is opened\cr 604 CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr 605 } 606 607 608 The initial value of this register is $CDO_AUTO_CLOSE \mathrel| 609 CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user 610 interface and software standards. Before you protest, there are two 611 new $ioctl$s implemented in \cdromc, that allow you to control the 612 behavior by software. These are: 613 614 \halign{#\ \hfil&/* \rm# */\hfil\cr 615 CDROM_SET_OPTIONS& set options specified in (int)\ arg\cr 616 CDROM_CLEAR_OPTIONS& clear options specified in (int)\ arg\cr 617 } 618 619 One option needs some more explanation: $CDO_USE_FFLAGS$. In the next 620 newsection we explain what the need for this option is. 621 622 A software package {\tt setcd}, available from the Debian distribution 623 and {\tt sunsite.unc.edu}, allows user level control of these flags. 624 625 \newsection{The need to know the purpose of opening the \cdrom\ device} 626 627 Traditionally, Unix devices can be used in two different modes', 628 either by reading/writing to the device file, or by issuing 629 controlling commands to the device, by the device's $ioctl()$ 630 call. The problem with \cdrom\ drives, is that they can be used for 631 two entirely different purposes. One is to mount removable 632 file systems, \cdrom s, the other is to play audio CD's. Audio commands 633 are implemented entirely through $ioctl$s, presumably because the 634 first implementation (SUN?) has been such. In principle there is 635 nothing wrong with this, but a good control of the CD player' demands 636 that the device can {\em always\/} be opened in order to give the 637 $ioctl$ commands, regardless of the state the drive is in. 638 639 On the other hand, when used as a removable-media disc drive (what the 640 original purpose of \cdrom s is) we would like to make sure that the 641 disc drive is ready for operation upon opening the device. In the old 642 scheme, some \cdrom\ drivers don't do any integrity checking, resulting 643 in a number of i/o errors reported by the VFS to the kernel when an 644 attempt for mounting a \cdrom\ on an empty drive occurs. This is not a 645 particularly elegant way to find out that there is no \cdrom\ inserted; 646 it more-or-less looks like the old IBM-PC trying to read an empty floppy 647 drive for a couple of seconds, after which the system complains it 648 can't read from it. Nowadays we can {\em sense\/} the existence of a 649 removable medium in a drive, and we believe we should exploit that 650 fact. An integrity check on opening of the device, that verifies the 651 availability of a \cdrom\ and its correct type (data), would be 652 desirable. 653 654 These two ways of using a \cdrom\ drive, principally for data and 655 secondarily for playing audio discs, have different demands for the 656 behavior of the $open()$ call. Audio use simply wants to open the 657 device in order to get a file handle which is needed for issuing 658 $ioctl$ commands, while data use wants to open for correct and 659 reliable data transfer. The only way user programs can indicate what 660 their {\em purpose\/} of opening the device is, is through the $flags$ 661 parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't 662 implemented (some drivers implement checking for write-related flags, 663 but this is not strictly necessary if the device file has correct 664 permission flags). Most option flags simply don't make sense to 665 \cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and 666 $O_SYNC$ have no meaning to a \cdrom. 667 668 We therefore propose to use the flag $O_NONBLOCK$ to indicate 669 that the device is opened just for issuing $ioctl$ 670 commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and 671 subsequent calls to the device don't cause the calling process to 672 wait. We could interpret this as don't wait until someone has 673 inserted some valid data-\cdrom.'' Thus, our proposal of the 674 implementation for the $open()$ call for \cdrom s is: 675 \begin{itemize} 676 \item If no other flags are set than $O_RDONLY$, the device is opened 677 for data transfer, and the return value will be 0 only upon successful 678 initialization of the transfer. The call may even induce some actions 679 on the \cdrom, such as closing the tray. 680 \item If the option flag $O_NONBLOCK$ is set, opening will always be 681 successful, unless the whole device doesn't exist. The drive will take 682 no actions whatsoever. 683 \end{itemize} 684 685 \subsection{And what about standards?} 686 687 You might hesitate to accept this proposal as it comes from the 688 \linux\ community, and not from some standardizing institute. What 689 about SUN, SGI, HP and all those other Unix and hardware vendors? 690 Well, these companies are in the lucky position that they generally 691 control both the hardware and software of their supported products, 692 and are large enough to set their own standard. They do not have to 693 deal with a dozen or more different, competing hardware 694 configurations.\footnote{Incidentally, I think that SUN's approach to 695 mounting \cdrom s is very good in origin: under Solaris a 696 volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt 697 {/cdrom/$$/}}. In my opinion they should have pushed this 698 further and have {\em every\/} \cdrom\ on the local area network be 699 mounted at the similar location, \ie, no matter in which particular 700 machine you insert a \cdrom, it will always appear at the same 701 position in the directory tree, on every system. When I wanted to 702 implement such a user-program for \linux, I came across the 703 differences in behavior of the various drivers, and the need for an 704 ioctl informing about media changes.} 705 706 We believe that using O_NONBLOCK to indicate that a device is being opened 707 for ioctl commands only can be easily introduced in the \linux\ 708 community. All the CD-player authors will have to be informed, we can 709 even send in our own patches to the programs. The use of O_NONBLOCK 710 has most likely no influence on the behavior of the CD-players on 711 other operating systems than \linux. Finally, a user can always revert 712 to old behavior by a call to ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, 713 CDO_USE_FFLAGS). 714 715 \subsection{The preferred strategy of open()} 716 717 The routines in \cdromc\ are designed in such a way that run-time 718 configuration of the behavior of \cdrom\ devices (of {\em any\/} type) 719 can be carried out, by the CDROM_SET/CLEAR_OPTIONS ioctls. Thus, various 720 modes of operation can be set: 721 \begin{description} 722 \item[CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK] This 723 is the default setting. (With CDO_CHECK_TYPE it will be better, in the 724 future.) If the device is not yet opened by any other process, and if 725 the device is being opened for data (O_NONBLOCK is not set) and the 726 tray is found to be open, an attempt to close the tray is made. Then, 727 it is verified that a disc is in the drive and, if CDO_CHECK_TYPE is 728 set, that it contains tracks of type data mode 1.' Only if all tests 729 are passed is the return value zero. The door is locked to prevent file 730 system corruption. If the drive is opened for audio (O_NONBLOCK is 731 set), no actions are taken and a value of 0 will be returned. 732 \item[CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK] This 733 mimics the behavior of the current sbpcd-driver. The option flags are 734 ignored, the tray is closed on the first open, if necessary. Similarly, 735 the tray is opened on the last release, \ie, if a \cdrom\ is unmounted, 736 it is automatically ejected, such that the user can replace it. 737 \end{description} 738 We hope that these option can convince everybody (both driver 739 maintainers and user program developers) to adopt the new \cdrom\ 740 driver scheme and option flag interpretation. 741 742 \newsection{Description of routines in \cdromc} 743 744 Only a few routines in \cdromc\ are exported to the drivers. In this 745 new section we will discuss these, as well as the functions that take 746 over' the \cdrom\ interface to the kernel. The header file belonging 747 to \cdromc\ is called \cdromh. Formerly, some of the contents of this 748 file were placed in the file {\tt {ucdrom.h}}, but this file has now been 749 merged back into \cdromh. 750 751 \subsection{Struct\ file_operations\ cdrom_fops} 752 753 The contents of this structure were described in section~\ref{cdrom.c}. 754 A pointer to this structure is assigned to the fops field 755 of the struct gendisk. 756 757 \subsection{Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)} 758 759 This function is used in about the same way one registers cdrom_fops 760 with the kernel, the device operations and information structures, 761 as described in section~\ref{cdrom.c}, should be registered with the 762 \UCD: 763$$ 764 register_cdrom(\&_info)); 765 $$766 This function returns zero upon success, and non-zero upon 767 failure. The structure _info should have a pointer to the 768 driver's _dops, as in 769$$ 770 \vbox{\halign{&$#$\hfil\cr 771 struct\ &cdrom_device_info\ _info = \{\cr 772 & _dops;\cr 773 &\ldots\cr 774 \}\cr 775 }}$$776 Note that a driver must have one static structure, _dops, while 777 it may have as many structures _info as there are minor devices 778 active. Register_cdrom() builds a linked list from these. 779 780 \subsection{Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)} 781 782 Unregistering device cdi with minor number MINOR(cdi\to dev) removes 783 the minor device from the list. If it was the last registered minor for 784 the low-level driver, this disconnects the registered device-operation 785 routines from the \cdrom\ interface. This function returns zero upon 786 success, and non-zero upon failure. 787 788 \subsection{Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)} 789 790 This function is not called directly by the low-level drivers, it is 791 listed in the standard cdrom_fops. If the VFS opens a file, this 792 function becomes active. A strategy is implemented in this routine, 793 taking care of all capabilities and options that are set in the 794 cdrom_device_ops connected to the device. Then, the program flow is 795 transferred to the device_dependent open() call. 796 797 \subsection{Void\ cdrom_release(struct\ inode *ip, struct\ file 798 *fp)} 799 800 This function implements the reverse-logic of cdrom_open(), and then 801 calls the device-dependent release() routine. When the use-count has 802 reached 0, the allocated buffers are flushed by calls to sync_dev(dev) 803 and invalidate_buffers(dev). 804 805 806 \subsection{Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp, 807 unsigned\ int\ cmd, unsigned\ long\ arg)} 808 \label{cdrom-ioctl} 809 810 This function handles all the standard ioctl requests for \cdrom\ 811 devices in a uniform way. The different calls fall into three 812 categories: ioctls that can be directly implemented by device 813 operations, ones that are routed through the call audio_ioctl(), and 814 the remaining ones, that are presumable device-dependent. Generally, a 815 negative return value indicates an error. 816 817 \subsubsection{Directly implemented ioctls} 818 \label{ioctl-direct} 819 820 The following old' \cdrom-ioctls are implemented by directly 821 calling device-operations in cdrom_device_ops, if implemented and 822 not masked: 823 \begin{description} 824 \item[CDROMMULTISESSION] Requests the last session on a \cdrom. 825 \item[CDROMEJECT] Open tray. 826 \item[CDROMCLOSETRAY] Close tray. 827 \item[CDROMEJECT_SW] If arg\not=0, set behavior to auto-close (close 828 tray on first open) and auto-eject (eject on last release), otherwise 829 set behavior to non-moving on open() and release() calls. 830 \item[CDROM_GET_MCN] Get the Media Catalog Number from a CD. 831 \end{description} 832 833 \subsubsection{Ioctls routed through audio_ioctl()} 834 \label{ioctl-audio} 835 836 The following set of ioctls are all implemented through a call to 837 the cdrom_fops function audio_ioctl(). Memory checks and 838 allocation are performed in cdrom_ioctl(), and also sanitization of 839 address format (CDROM_LBA/CDROM_MSF) is done. 840 \begin{description} 841 \item[CDROMSUBCHNL] Get sub-channel data in argument arg of type struct\ 842 cdrom_subchnl *{}. 843 \item[CDROMREADTOCHDR] Read Table of Contents header, in arg of type 844 struct\ cdrom_tochdr *{}. 845 \item[CDROMREADTOCENTRY] Read a Table of Contents entry in arg and 846 specified by arg of type struct\ cdrom_tocentry *{}. 847 \item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second, 848 Frame format, delimited by arg of type struct\ cdrom_msf *{}. 849 \item[CDROMPLAYTRKIND] Play audio fragment in track-index format 850 delimited by arg of type struct\ \penalty-1000 cdrom_ti *{}. 851 \item[CDROMVOLCTRL] Set volume specified by arg of type struct\ 852 cdrom_volctrl *{}. 853 \item[CDROMVOLREAD] Read volume into by arg of type struct\ 854 cdrom_volctrl *{}. 855 \item[CDROMSTART] Spin up disc. 856 \item[CDROMSTOP] Stop playback of audio fragment. 857 \item[CDROMPAUSE] Pause playback of audio fragment. 858 \item[CDROMRESUME] Resume playing. 859 \end{description} 860 861 \subsubsection{New ioctls in \cdromc} 862 863 The following ioctls have been introduced to allow user programs to 864 control the behavior of individual \cdrom\ devices. New ioctl 865 commands can be identified by the underscores in their names. 866 \begin{description} 867 \item[CDROM_SET_OPTIONS] Set options specified by arg. Returns the 868 option flag register after modification. Use arg = \rm0 for reading 869 the current flags. 870 \item[CDROM_CLEAR_OPTIONS] Clear options specified by arg. Returns 871 the option flag register after modification. 872 \item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as 873 by arg in units of standard cdrom speed (176\,kB/sec raw data or 874 150\,kB/sec file system data). The value 0 means `auto-select', \ie, 875 play audio discs at real time and data discs at maximum speed. The value 876 arg is checked against the maximum head rate of the drive found in the 877 cdrom_dops. 878 \item[CDROM_SELECT_DISC] Select disc numbered arg from a juke-box. 879 First disc is numbered 0. The number arg is checked against the 880 maximum number of discs in the juke-box found in the cdrom_dops. 881 \item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since 882 the last call. Note that calls to cdrom_media_changed by the VFS 883 are treated by an independent queue, so both mechanisms will detect 884 a media change once. For juke-boxes, an extra argument arg 885 specifies the slot for which the information is given. The special 886 value CDSL_CURRENT requests that information about the currently 887 selected slot be returned. 888 \item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to 889 drive_status(). Return values are defined in section~\ref{drive 890 status}. Note that this call doesn't return information on the 891 current playing activity of the drive; this can be polled through an 892 ioctl call to CDROMSUBCHNL. For juke-boxes, an extra argument 893 arg specifies the slot for which (possibly limited) information is 894 given. The special value CDSL_CURRENT requests that information 895 about the currently selected slot be returned. 896 \item[CDROM_DISC_STATUS] Returns the type of the disc currently in the 897 drive. It should be viewed as a complement to CDROM_DRIVE_STATUS. 898 This ioctl can provide \emph {some} information about the current 899 disc that is inserted in the drive. This functionality used to be 900 implemented in the low level drivers, but is now carried out 901 entirely in \UCD. 902 903 The history of development of the CD's use as a carrier medium for 904 various digital information has lead to many different disc types. 905 This ioctl is useful only in the case that CDs have \emph {only 906 one} type of data on them. While this is often the case, it is 907 also very common for CDs to have some tracks with data, and some 908 tracks with audio. Because this is an existing interface, rather 909 than fixing this interface by changing the assumptions it was made 910 under, thereby breaking all user applications that use this 911 function, the \UCD\ implements this ioctl as follows: If the CD in 912 question has audio tracks on it, and it has absolutely no CD-I, XA, 913 or data tracks on it, it will be reported as CDS_AUDIO. If it has 914 both audio and data tracks, it will return CDS_MIXED. If there 915 are no audio tracks on the disc, and if the CD in question has any 916 CD-I tracks on it, it will be reported as CDS_XA_2_2. Failing 917 that, if the CD in question has any XA tracks on it, it will be 918 reported as CDS_XA_2_1. Finally, if the CD in question has any 919 data tracks on it, it will be reported as a data CD (CDS_DATA_1). 920 921 This ioctl can return: 922$$ 923 \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr 924 CDS_NO_INFO& no information available\cr 925 CDS_NO_DISC& no disc is inserted, or tray is opened\cr 926 CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr 927 CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr 928 CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr 929 CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324 user bytes)\cr 930 CDS_MIXED& mixed audio/data disc\cr 931 } 932 $$933 For some information concerning frame layout of the various disc 934 types, see a recent version of \cdromh. 935 936 \item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a 937 juke-box. 938 \item[CDROMRESET] Reset the drive. 939 \item[CDROM_GET_CAPABILITY] Returns the capability flags for the 940 drive. Refer to section \ref{capability} for more information on 941 these flags. 942 \item[CDROM_LOCKDOOR] Locks the door of the drive. arg == \rm0 943 unlocks the door, any other value locks it. 944 \item[CDROM_DEBUG] Turns on debugging info. Only root is allowed 945 to do this. Same semantics as CDROM_LOCKDOOR. 946 \end{description} 947 948 \subsubsection{Device dependent ioctls} 949 950 Finally, all other ioctls are passed to the function dev_ioctl(), 951 if implemented. No memory allocation or verification is carried out. 952 953 \newsection{How to update your driver} 954 955 \begin{enumerate} 956 \item Make a backup of your current driver. 957 \item Get hold of the files \cdromc\ and \cdromh, they should be in 958 the directory tree that came with this documentation. 959 \item Make sure you include \cdromh. 960 \item Change the 3rd argument of register_blkdev from 961 \&_fops to \&cdrom_fops. 962 \item Just after that line, add the following to register with the \UCD: 963$$register_cdrom(\&_info);$$964 Similarly, add a call to unregister_cdrom() at the appropriate place. 965 \item Copy an example of the device-operations struct to your 966 source, \eg, from {\tt {cm206.c}} cm206_dops, and change all 967 entries to names corresponding to your driver, or names you just 968 happen to like. If your driver doesn't support a certain function, 969 make the entry NULL. At the entry capability you should list all 970 capabilities your driver currently supports. If your driver 971 has a capability that is not listed, please send me a message. 972 \item Copy the cdrom_device_info declaration from the same example 973 driver, and modify the entries according to your needs. If your 974 driver dynamically determines the capabilities of the hardware, this 975 structure should also be declared dynamically. 976 \item Implement all functions in your _dops structure, 977 according to prototypes listed in \cdromh, and specifications given 978 in section~\ref{cdrom.c}. Most likely you have already implemented 979 the code in a large part, and you will almost certainly need to adapt the 980 prototype and return values. 981 \item Rename your _ioctl() function to audio_ioctl and 982 change the prototype a little. Remove entries listed in the first 983 part in section~\ref{cdrom-ioctl}, if your code was OK, these are 984 just calls to the routines you adapted in the previous step. 985 \item You may remove all remaining memory checking code in the 986 audio_ioctl() function that deals with audio commands (these are 987 listed in the second part of section~\ref{cdrom-ioctl}). There is no 988 need for memory allocation either, so most cases in the switch 989 statement look similar to: 990$$ 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, $_ioctl$, the device-dependent $ioctl$s. Note that 996 memory checking and allocation must be kept in this code! 997 \item Change the prototypes of $_open()$ and 998 $_release()$, and remove any strategic code (\ie, tray 999 movement, door locking, etc.). 1000 \item Try to recompile the drivers. We advise you to use modules, both 1001 for {\tt {cdrom.o}} and your driver, as debugging is much easier this 1002 way. 1003 \end{enumerate} 1004 1005 \newsection{Thanks} 1006 1007 Thanks to all the people involved. First, Erik Andersen, who has 1008 taken over the torch in maintaining \cdromc\ and integrating much 1009 \cdrom-related code in the 2.1-kernel. Thanks to Scott Snyder and 1010 Gerd Knorr, who were the first to implement this interface for SCSI 1011 and IDE-CD drivers and added many ideas for extension of the data 1012 structures relative to kernel~2.0. Further thanks to Heiko Ei{\sz}feldt, 1013 Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew 1014 Kroll, the \linux\ \cdrom\ device driver developers who were kind 1015 enough to give suggestions and criticisms during the writing. Finally 1016 of course, I want to thank Linus Torvalds for making this possible in 1017 the first place. 1018 1019 \vfill 1020 $\version\$ 1021 \eject 1022 \end{document} 1023