1======================= 2A Linux CD-ROM standard 3======================= 4 5:Author: David van Leeuwen <david@ElseWare.cistron.nl> 6:Date: 12 March 1999 7:Updated by: Erik Andersen (andersee@debian.org) 8:Updated by: Jens Axboe (axboe@image.dk) 9 10 11Introduction 12============ 13 14Linux is probably the Unix-like operating system that supports 15the widest variety of hardware devices. The reasons for this are 16presumably 17 18- The large list of hardware devices available for the many platforms 19 that Linux now supports (i.e., i386-PCs, Sparc Suns, etc.) 20- The open design of the operating system, such that anybody can write a 21 driver for Linux. 22- There is plenty of source code around as examples of how to write a driver. 23 24The openness of Linux, and the many different types of available 25hardware has allowed Linux to support many different hardware devices. 26Unfortunately, the very openness that has allowed Linux to support 27all these different devices has also allowed the behavior of each 28device driver to differ significantly from one device to another. 29This divergence of behavior has been very significant for CD-ROM 30devices; the way a particular drive reacts to a `standard` *ioctl()* 31call varies greatly from one device driver to another. To avoid making 32their drivers totally inconsistent, the writers of Linux CD-ROM 33drivers generally created new device drivers by understanding, copying, 34and then changing an existing one. Unfortunately, this practice did not 35maintain uniform behavior across all the Linux CD-ROM drivers. 36 37This document describes an effort to establish Uniform behavior across 38all the different CD-ROM device drivers for Linux. This document also 39defines the various *ioctl()'s*, and how the low-level CD-ROM device 40drivers should implement them. Currently (as of the Linux 2.1.\ *x* 41development kernels) several low-level CD-ROM device drivers, including 42both IDE/ATAPI and SCSI, now use this Uniform interface. 43 44When the CD-ROM was developed, the interface between the CD-ROM drive 45and the computer was not specified in the standards. As a result, many 46different CD-ROM interfaces were developed. Some of them had their 47own proprietary design (Sony, Mitsumi, Panasonic, Philips), other 48manufacturers adopted an existing electrical interface and changed 49the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply 50adapted their drives to one or more of the already existing electrical 51interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and 52most of the `NoName` manufacturers). In cases where a new drive really 53brought its own interface or used its own command set and flow control 54scheme, either a separate driver had to be written, or an existing 55driver had to be enhanced. History has delivered us CD-ROM support for 56many of these different interfaces. Nowadays, almost all new CD-ROM 57drives are either IDE/ATAPI or SCSI, and it is very unlikely that any 58manufacturer will create a new interface. Even finding drives for the 59old proprietary interfaces is getting difficult. 60 61When (in the 1.3.70's) I looked at the existing software interface, 62which was expressed through `cdrom.h`, it appeared to be a rather wild 63set of commands and data formats [#f1]_. It seemed that many 64features of the software interface had been added to accommodate the 65capabilities of a particular drive, in an *ad hoc* manner. More 66importantly, it appeared that the behavior of the `standard` commands 67was different for most of the different drivers: e. g., some drivers 68close the tray if an *open()* call occurs when the tray is open, while 69others do not. Some drivers lock the door upon opening the device, to 70prevent an incoherent file system, but others don't, to allow software 71ejection. Undoubtedly, the capabilities of the different drives vary, 72but even when two drives have the same capability their drivers' 73behavior was usually different. 74 75.. [#f1] 76 I cannot recollect what kernel version I looked at, then, 77 presumably 1.2.13 and 1.3.34 --- the latest kernel that I was 78 indirectly involved in. 79 80I decided to start a discussion on how to make all the Linux CD-ROM 81drivers behave more uniformly. I began by contacting the developers of 82the many CD-ROM drivers found in the Linux kernel. Their reactions 83encouraged me to write the Uniform CD-ROM Driver which this document is 84intended to describe. The implementation of the Uniform CD-ROM Driver is 85in the file `cdrom.c`. This driver is intended to be an additional software 86layer that sits on top of the low-level device drivers for each CD-ROM drive. 87By adding this additional layer, it is possible to have all the different 88CD-ROM devices behave **exactly** the same (insofar as the underlying 89hardware will allow). 90 91The goal of the Uniform CD-ROM Driver is **not** to alienate driver developers 92whohave not yet taken steps to support this effort. The goal of Uniform CD-ROM 93Driver is simply to give people writing application programs for CD-ROM drives 94**one** Linux CD-ROM interface with consistent behavior for all 95CD-ROM devices. In addition, this also provides a consistent interface 96between the low-level device driver code and the Linux kernel. Care 97is taken that 100% compatibility exists with the data structures and 98programmer's interface defined in `cdrom.h`. This guide was written to 99help CD-ROM driver developers adapt their code to use the Uniform CD-ROM 100Driver code defined in `cdrom.c`. 101 102Personally, I think that the most important hardware interfaces are 103the IDE/ATAPI drives and, of course, the SCSI drives, but as prices 104of hardware drop continuously, it is also likely that people may have 105more than one CD-ROM drive, possibly of mixed types. It is important 106that these drives behave in the same way. In December 1994, one of the 107cheapest CD-ROM drives was a Philips cm206, a double-speed proprietary 108drive. In the months that I was busy writing a Linux driver for it, 109proprietary drives became obsolete and IDE/ATAPI drives became the 110standard. At the time of the last update to this document (November 1111997) it is becoming difficult to even **find** anything less than a 11216 speed CD-ROM drive, and 24 speed drives are common. 113 114.. _cdrom_api: 115 116Standardizing through another software level 117============================================ 118 119At the time this document was conceived, all drivers directly 120implemented the CD-ROM *ioctl()* calls through their own routines. This 121led to the danger of different drivers forgetting to do important things 122like checking that the user was giving the driver valid data. More 123importantly, this led to the divergence of behavior, which has already 124been discussed. 125 126For this reason, the Uniform CD-ROM Driver was created to enforce consistent 127CD-ROM drive behavior, and to provide a common set of services to the various 128low-level CD-ROM device drivers. The Uniform CD-ROM Driver now provides another 129software-level, that separates the *ioctl()* and *open()* implementation 130from the actual hardware implementation. Note that this effort has 131made few changes which will affect a user's application programs. The 132greatest change involved moving the contents of the various low-level 133CD-ROM drivers\' header files to the kernel's cdrom directory. This was 134done to help ensure that the user is only presented with only one cdrom 135interface, the interface defined in `cdrom.h`. 136 137CD-ROM drives are specific enough (i. e., different from other 138block-devices such as floppy or hard disc drives), to define a set 139of common **CD-ROM device operations**, *<cdrom-device>_dops*. 140These operations are different from the classical block-device file 141operations, *<block-device>_fops*. 142 143The routines for the Uniform CD-ROM Driver interface level are implemented 144in the file `cdrom.c`. In this file, the Uniform CD-ROM Driver interfaces 145with the kernel as a block device by registering the following general 146*struct file_operations*:: 147 148 struct file_operations cdrom_fops = { 149 NULL, /∗ lseek ∗/ 150 block _read , /∗ read—general block-dev read ∗/ 151 block _write, /∗ write—general block-dev write ∗/ 152 NULL, /∗ readdir ∗/ 153 NULL, /∗ select ∗/ 154 cdrom_ioctl, /∗ ioctl ∗/ 155 NULL, /∗ mmap ∗/ 156 cdrom_open, /∗ open ∗/ 157 cdrom_release, /∗ release ∗/ 158 NULL, /∗ fsync ∗/ 159 NULL, /∗ fasync ∗/ 160 cdrom_media_changed, /∗ media change ∗/ 161 NULL /∗ revalidate ∗/ 162 }; 163 164Every active CD-ROM device shares this *struct*. The routines 165declared above are all implemented in `cdrom.c`, since this file is the 166place where the behavior of all CD-ROM-devices is defined and 167standardized. The actual interface to the various types of CD-ROM 168hardware is still performed by various low-level CD-ROM-device 169drivers. These routines simply implement certain **capabilities** 170that are common to all CD-ROM (and really, all removable-media 171devices). 172 173Registration of a low-level CD-ROM device driver is now done through 174the general routines in `cdrom.c`, not through the Virtual File System 175(VFS) any more. The interface implemented in `cdrom.c` is carried out 176through two general structures that contain information about the 177capabilities of the driver, and the specific drives on which the 178driver operates. The structures are: 179 180cdrom_device_ops 181 This structure contains information about the low-level driver for a 182 CD-ROM device. This structure is conceptually connected to the major 183 number of the device (although some drivers may have different 184 major numbers, as is the case for the IDE driver). 185 186cdrom_device_info 187 This structure contains information about a particular CD-ROM drive, 188 such as its device name, speed, etc. This structure is conceptually 189 connected to the minor number of the device. 190 191Registering a particular CD-ROM drive with the Uniform CD-ROM Driver 192is done by the low-level device driver though a call to:: 193 194 register_cdrom(struct cdrom_device_info * <device>_info) 195 196The device information structure, *<device>_info*, contains all the 197information needed for the kernel to interface with the low-level 198CD-ROM device driver. One of the most important entries in this 199structure is a pointer to the *cdrom_device_ops* structure of the 200low-level driver. 201 202The device operations structure, *cdrom_device_ops*, contains a list 203of pointers to the functions which are implemented in the low-level 204device driver. When `cdrom.c` accesses a CD-ROM device, it does it 205through the functions in this structure. It is impossible to know all 206the capabilities of future CD-ROM drives, so it is expected that this 207list may need to be expanded from time to time as new technologies are 208developed. For example, CD-R and CD-R/W drives are beginning to become 209popular, and support will soon need to be added for them. For now, the 210current *struct* is:: 211 212 struct cdrom_device_ops { 213 int (*open)(struct cdrom_device_info *, int) 214 void (*release)(struct cdrom_device_info *); 215 int (*drive_status)(struct cdrom_device_info *, int); 216 unsigned int (*check_events)(struct cdrom_device_info *, 217 unsigned int, int); 218 int (*media_changed)(struct cdrom_device_info *, int); 219 int (*tray_move)(struct cdrom_device_info *, int); 220 int (*lock_door)(struct cdrom_device_info *, int); 221 int (*select_speed)(struct cdrom_device_info *, int); 222 int (*select_disc)(struct cdrom_device_info *, int); 223 int (*get_last_session) (struct cdrom_device_info *, 224 struct cdrom_multisession *); 225 int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *); 226 int (*reset)(struct cdrom_device_info *); 227 int (*audio_ioctl)(struct cdrom_device_info *, 228 unsigned int, void *); 229 const int capability; /* capability flags */ 230 int (*generic_packet)(struct cdrom_device_info *, 231 struct packet_command *); 232 }; 233 234When a low-level device driver implements one of these capabilities, 235it should add a function pointer to this *struct*. When a particular 236function is not implemented, however, this *struct* should contain a 237NULL instead. The *capability* flags specify the capabilities of the 238CD-ROM hardware and/or low-level CD-ROM driver when a CD-ROM drive 239is registered with the Uniform CD-ROM Driver. 240 241Note that most functions have fewer parameters than their 242*blkdev_fops* counterparts. This is because very little of the 243information in the structures *inode* and *file* is used. For most 244drivers, the main parameter is the *struct* *cdrom_device_info*, from 245which the major and minor number can be extracted. (Most low-level 246CD-ROM drivers don't even look at the major and minor number though, 247since many of them only support one device.) This will be available 248through *dev* in *cdrom_device_info* described below. 249 250The drive-specific, minor-like information that is registered with 251`cdrom.c`, currently contains the following fields:: 252 253 struct cdrom_device_info { 254 const struct cdrom_device_ops * ops; /* device operations for this major */ 255 struct list_head list; /* linked list of all device_info */ 256 struct gendisk * disk; /* matching block layer disk */ 257 void * handle; /* driver-dependent data */ 258 259 int mask; /* mask of capability: disables them */ 260 int speed; /* maximum speed for reading data */ 261 int capacity; /* number of discs in a jukebox */ 262 263 unsigned int options:30; /* options flags */ 264 unsigned mc_flags:2; /* media-change buffer flags */ 265 unsigned int vfs_events; /* cached events for vfs path */ 266 unsigned int ioctl_events; /* cached events for ioctl path */ 267 int use_count; /* number of times device is opened */ 268 char name[20]; /* name of the device type */ 269 270 __u8 sanyo_slot : 2; /* Sanyo 3-CD changer support */ 271 __u8 keeplocked : 1; /* CDROM_LOCKDOOR status */ 272 __u8 reserved : 5; /* not used yet */ 273 int cdda_method; /* see CDDA_* flags */ 274 __u8 last_sense; /* saves last sense key */ 275 __u8 media_written; /* dirty flag, DVD+RW bookkeeping */ 276 unsigned short mmc3_profile; /* current MMC3 profile */ 277 int for_data; /* unknown:TBD */ 278 int (*exit)(struct cdrom_device_info *);/* unknown:TBD */ 279 int mrw_mode_page; /* which MRW mode page is in use */ 280 }; 281 282Using this *struct*, a linked list of the registered minor devices is 283built, using the *next* field. The device number, the device operations 284struct and specifications of properties of the drive are stored in this 285structure. 286 287The *mask* flags can be used to mask out some of the capabilities listed 288in *ops->capability*, if a specific drive doesn't support a feature 289of the driver. The value *speed* specifies the maximum head-rate of the 290drive, measured in units of normal audio speed (176kB/sec raw data or 291150kB/sec file system data). The parameters are declared *const* 292because they describe properties of the drive, which don't change after 293registration. 294 295A few registers contain variables local to the CD-ROM drive. The 296flags *options* are used to specify how the general CD-ROM routines 297should behave. These various flags registers should provide enough 298flexibility to adapt to the different users' wishes (and **not** the 299`arbitrary` wishes of the author of the low-level device driver, as is 300the case in the old scheme). The register *mc_flags* is used to buffer 301the information from *media_changed()* to two separate queues. Other 302data that is specific to a minor drive, can be accessed through *handle*, 303which can point to a data structure specific to the low-level driver. 304The fields *use_count*, *next*, *options* and *mc_flags* need not be 305initialized. 306 307The intermediate software layer that `cdrom.c` forms will perform some 308additional bookkeeping. The use count of the device (the number of 309processes that have the device opened) is registered in *use_count*. The 310function *cdrom_ioctl()* will verify the appropriate user-memory regions 311for read and write, and in case a location on the CD is transferred, 312it will `sanitize` the format by making requests to the low-level 313drivers in a standard format, and translating all formats between the 314user-software and low level drivers. This relieves much of the drivers' 315memory checking and format checking and translation. Also, the necessary 316structures will be declared on the program stack. 317 318The implementation of the functions should be as defined in the 319following sections. Two functions **must** be implemented, namely 320*open()* and *release()*. Other functions may be omitted, their 321corresponding capability flags will be cleared upon registration. 322Generally, a function returns zero on success and negative on error. A 323function call should return only after the command has completed, but of 324course waiting for the device should not use processor time. 325 326:: 327 328 int open(struct cdrom_device_info *cdi, int purpose) 329 330*Open()* should try to open the device for a specific *purpose*, which 331can be either: 332 333- Open for reading data, as done by `mount()` (2), or the 334 user commands `dd` or `cat`. 335- Open for *ioctl* commands, as done by audio-CD playing programs. 336 337Notice that any strategic code (closing tray upon *open()*, etc.) is 338done by the calling routine in `cdrom.c`, so the low-level routine 339should only be concerned with proper initialization, such as spinning 340up the disc, etc. 341 342:: 343 344 void release(struct cdrom_device_info *cdi) 345 346Device-specific actions should be taken such as spinning down the device. 347However, strategic actions such as ejection of the tray, or unlocking 348the door, should be left over to the general routine *cdrom_release()*. 349This is the only function returning type *void*. 350 351.. _cdrom_drive_status: 352 353:: 354 355 int drive_status(struct cdrom_device_info *cdi, int slot_nr) 356 357The function *drive_status*, if implemented, should provide 358information on the status of the drive (not the status of the disc, 359which may or may not be in the drive). If the drive is not a changer, 360*slot_nr* should be ignored. In `cdrom.h` the possibilities are listed:: 361 362 363 CDS_NO_INFO /* no information available */ 364 CDS_NO_DISC /* no disc is inserted, tray is closed */ 365 CDS_TRAY_OPEN /* tray is opened */ 366 CDS_DRIVE_NOT_READY /* something is wrong, tray is moving? */ 367 CDS_DISC_OK /* a disc is loaded and everything is fine */ 368 369:: 370 371 int media_changed(struct cdrom_device_info *cdi, int disc_nr) 372 373This function is very similar to the original function in $struct 374file_operations*. It returns 1 if the medium of the device *cdi->dev* 375has changed since the last call, and 0 otherwise. The parameter 376*disc_nr* identifies a specific slot in a juke-box, it should be 377ignored for single-disc drives. Note that by `re-routing` this 378function through *cdrom_media_changed()*, we can implement separate 379queues for the VFS and a new *ioctl()* function that can report device 380changes to software (e. g., an auto-mounting daemon). 381 382:: 383 384 int tray_move(struct cdrom_device_info *cdi, int position) 385 386This function, if implemented, should control the tray movement. (No 387other function should control this.) The parameter *position* controls 388the desired direction of movement: 389 390- 0 Close tray 391- 1 Open tray 392 393This function returns 0 upon success, and a non-zero value upon 394error. Note that if the tray is already in the desired position, no 395action need be taken, and the return value should be 0. 396 397:: 398 399 int lock_door(struct cdrom_device_info *cdi, int lock) 400 401This function (and no other code) controls locking of the door, if the 402drive allows this. The value of *lock* controls the desired locking 403state: 404 405- 0 Unlock door, manual opening is allowed 406- 1 Lock door, tray cannot be ejected manually 407 408This function returns 0 upon success, and a non-zero value upon 409error. Note that if the door is already in the requested state, no 410action need be taken, and the return value should be 0. 411 412:: 413 414 int select_speed(struct cdrom_device_info *cdi, int speed) 415 416Some CD-ROM drives are capable of changing their head-speed. There 417are several reasons for changing the speed of a CD-ROM drive. Badly 418pressed CD-ROM s may benefit from less-than-maximum head rate. Modern 419CD-ROM drives can obtain very high head rates (up to *24x* is 420common). It has been reported that these drives can make reading 421errors at these high speeds, reducing the speed can prevent data loss 422in these circumstances. Finally, some of these drives can 423make an annoyingly loud noise, which a lower speed may reduce. 424 425This function specifies the speed at which data is read or audio is 426played back. The value of *speed* specifies the head-speed of the 427drive, measured in units of standard cdrom speed (176kB/sec raw data 428or 150kB/sec file system data). So to request that a CD-ROM drive 429operate at 300kB/sec you would call the CDROM_SELECT_SPEED *ioctl* 430with *speed=2*. The special value `0` means `auto-selection`, i. e., 431maximum data-rate or real-time audio rate. If the drive doesn't have 432this `auto-selection` capability, the decision should be made on the 433current disc loaded and the return value should be positive. A negative 434return value indicates an error. 435 436:: 437 438 int select_disc(struct cdrom_device_info *cdi, int number) 439 440If the drive can store multiple discs (a juke-box) this function 441will perform disc selection. It should return the number of the 442selected disc on success, a negative value on error. Currently, only 443the ide-cd driver supports this functionality. 444 445:: 446 447 int get_last_session(struct cdrom_device_info *cdi, 448 struct cdrom_multisession *ms_info) 449 450This function should implement the old corresponding *ioctl()*. For 451device *cdi->dev*, the start of the last session of the current disc 452should be returned in the pointer argument *ms_info*. Note that 453routines in `cdrom.c` have sanitized this argument: its requested 454format will **always** be of the type *CDROM_LBA* (linear block 455addressing mode), whatever the calling software requested. But 456sanitization goes even further: the low-level implementation may 457return the requested information in *CDROM_MSF* format if it wishes so 458(setting the *ms_info->addr_format* field appropriately, of 459course) and the routines in `cdrom.c` will make the transformation if 460necessary. The return value is 0 upon success. 461 462:: 463 464 int get_mcn(struct cdrom_device_info *cdi, 465 struct cdrom_mcn *mcn) 466 467Some discs carry a `Media Catalog Number` (MCN), also called 468`Universal Product Code` (UPC). This number should reflect the number 469that is generally found in the bar-code on the product. Unfortunately, 470the few discs that carry such a number on the disc don't even use the 471same format. The return argument to this function is a pointer to a 472pre-declared memory region of type *struct cdrom_mcn*. The MCN is 473expected as a 13-character string, terminated by a null-character. 474 475:: 476 477 int reset(struct cdrom_device_info *cdi) 478 479This call should perform a hard-reset on the drive (although in 480circumstances that a hard-reset is necessary, a drive may very well not 481listen to commands anymore). Preferably, control is returned to the 482caller only after the drive has finished resetting. If the drive is no 483longer listening, it may be wise for the underlying low-level cdrom 484driver to time out. 485 486:: 487 488 int audio_ioctl(struct cdrom_device_info *cdi, 489 unsigned int cmd, void *arg) 490 491Some of the CD-ROM-\ *ioctl()*\ 's defined in `cdrom.h` can be 492implemented by the routines described above, and hence the function 493*cdrom_ioctl* will use those. However, most *ioctl()*\ 's deal with 494audio-control. We have decided to leave these to be accessed through a 495single function, repeating the arguments *cmd* and *arg*. Note that 496the latter is of type *void*, rather than *unsigned long int*. 497The routine *cdrom_ioctl()* does do some useful things, 498though. It sanitizes the address format type to *CDROM_MSF* (Minutes, 499Seconds, Frames) for all audio calls. It also verifies the memory 500location of *arg*, and reserves stack-memory for the argument. This 501makes implementation of the *audio_ioctl()* much simpler than in the 502old driver scheme. For example, you may look up the function 503*cm206_audio_ioctl()* `cm206.c` that should be updated with 504this documentation. 505 506An unimplemented ioctl should return *-ENOSYS*, but a harmless request 507(e. g., *CDROMSTART*) may be ignored by returning 0 (success). Other 508errors should be according to the standards, whatever they are. When 509an error is returned by the low-level driver, the Uniform CD-ROM Driver 510tries whenever possible to return the error code to the calling program. 511(We may decide to sanitize the return value in *cdrom_ioctl()* though, in 512order to guarantee a uniform interface to the audio-player software.) 513 514:: 515 516 int dev_ioctl(struct cdrom_device_info *cdi, 517 unsigned int cmd, unsigned long arg) 518 519Some *ioctl()'s* seem to be specific to certain CD-ROM drives. That is, 520they are introduced to service some capabilities of certain drives. In 521fact, there are 6 different *ioctl()'s* for reading data, either in some 522particular kind of format, or audio data. Not many drives support 523reading audio tracks as data, I believe this is because of protection 524of copyrights of artists. Moreover, I think that if audio-tracks are 525supported, it should be done through the VFS and not via *ioctl()'s*. A 526problem here could be the fact that audio-frames are 2352 bytes long, 527so either the audio-file-system should ask for 75264 bytes at once 528(the least common multiple of 512 and 2352), or the drivers should 529bend their backs to cope with this incoherence (to which I would be 530opposed). Furthermore, it is very difficult for the hardware to find 531the exact frame boundaries, since there are no synchronization headers 532in audio frames. Once these issues are resolved, this code should be 533standardized in `cdrom.c`. 534 535Because there are so many *ioctl()'s* that seem to be introduced to 536satisfy certain drivers [#f2]_, any non-standard *ioctl()*\ s 537are routed through the call *dev_ioctl()*. In principle, `private` 538*ioctl()*\ 's should be numbered after the device's major number, and not 539the general CD-ROM *ioctl* number, `0x53`. Currently the 540non-supported *ioctl()'s* are: 541 542 CDROMREADMODE1, CDROMREADMODE2, CDROMREADAUDIO, CDROMREADRAW, 543 CDROMREADCOOKED, CDROMSEEK, CDROMPLAY-BLK and CDROM-READALL 544 545.. [#f2] 546 547 Is there software around that actually uses these? I'd be interested! 548 549.. _cdrom_capabilities: 550 551CD-ROM capabilities 552------------------- 553 554Instead of just implementing some *ioctl* calls, the interface in 555`cdrom.c` supplies the possibility to indicate the **capabilities** 556of a CD-ROM drive. This can be done by ORing any number of 557capability-constants that are defined in `cdrom.h` at the registration 558phase. Currently, the capabilities are any of:: 559 560 CDC_CLOSE_TRAY /* can close tray by software control */ 561 CDC_OPEN_TRAY /* can open tray */ 562 CDC_LOCK /* can lock and unlock the door */ 563 CDC_SELECT_SPEED /* can select speed, in units of * sim*150 ,kB/s */ 564 CDC_SELECT_DISC /* drive is juke-box */ 565 CDC_MULTI_SESSION /* can read sessions *> rm1* */ 566 CDC_MCN /* can read Media Catalog Number */ 567 CDC_MEDIA_CHANGED /* can report if disc has changed */ 568 CDC_PLAY_AUDIO /* can perform audio-functions (play, pause, etc) */ 569 CDC_RESET /* hard reset device */ 570 CDC_IOCTLS /* driver has non-standard ioctls */ 571 CDC_DRIVE_STATUS /* driver implements drive status */ 572 573The capability flag is declared *const*, to prevent drivers from 574accidentally tampering with the contents. The capability fags actually 575inform `cdrom.c` of what the driver can do. If the drive found 576by the driver does not have the capability, is can be masked out by 577the *cdrom_device_info* variable *mask*. For instance, the SCSI CD-ROM 578driver has implemented the code for loading and ejecting CD-ROM's, and 579hence its corresponding flags in *capability* will be set. But a SCSI 580CD-ROM drive might be a caddy system, which can't load the tray, and 581hence for this drive the *cdrom_device_info* struct will have set 582the *CDC_CLOSE_TRAY* bit in *mask*. 583 584In the file `cdrom.c` you will encounter many constructions of the type:: 585 586 if (cdo->capability & ∼cdi->mask & CDC _⟨capability⟩) ... 587 588There is no *ioctl* to set the mask... The reason is that 589I think it is better to control the **behavior** rather than the 590**capabilities**. 591 592Options 593------- 594 595A final flag register controls the **behavior** of the CD-ROM 596drives, in order to satisfy different users' wishes, hopefully 597independently of the ideas of the respective author who happened to 598have made the drive's support available to the Linux community. The 599current behavior options are:: 600 601 CDO_AUTO_CLOSE /* try to close tray upon device open() */ 602 CDO_AUTO_EJECT /* try to open tray on last device close() */ 603 CDO_USE_FFLAGS /* use file_pointer->f_flags to indicate purpose for open() */ 604 CDO_LOCK /* try to lock door if device is opened */ 605 CDO_CHECK_TYPE /* ensure disc type is data if opened for data */ 606 607The initial value of this register is 608`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK`, reflecting my own view on user 609interface and software standards. Before you protest, there are two 610new *ioctl()'s* implemented in `cdrom.c`, that allow you to control the 611behavior by software. These are:: 612 613 CDROM_SET_OPTIONS /* set options specified in (int)arg */ 614 CDROM_CLEAR_OPTIONS /* clear options specified in (int)arg */ 615 616One option needs some more explanation: *CDO_USE_FFLAGS*. In the next 617newsection we explain what the need for this option is. 618 619A software package `setcd`, available from the Debian distribution 620and `sunsite.unc.edu`, allows user level control of these flags. 621 622 623The need to know the purpose of opening the CD-ROM device 624========================================================= 625 626Traditionally, Unix devices can be used in two different `modes`, 627either by reading/writing to the device file, or by issuing 628controlling commands to the device, by the device's *ioctl()* 629call. The problem with CD-ROM drives, is that they can be used for 630two entirely different purposes. One is to mount removable 631file systems, CD-ROM's, the other is to play audio CD's. Audio commands 632are implemented entirely through *ioctl()\'s*, presumably because the 633first implementation (SUN?) has been such. In principle there is 634nothing wrong with this, but a good control of the `CD player` demands 635that the device can **always** be opened in order to give the 636*ioctl* commands, regardless of the state the drive is in. 637 638On the other hand, when used as a removable-media disc drive (what the 639original purpose of CD-ROM s is) we would like to make sure that the 640disc drive is ready for operation upon opening the device. In the old 641scheme, some CD-ROM drivers don't do any integrity checking, resulting 642in a number of i/o errors reported by the VFS to the kernel when an 643attempt for mounting a CD-ROM on an empty drive occurs. This is not a 644particularly elegant way to find out that there is no CD-ROM inserted; 645it more-or-less looks like the old IBM-PC trying to read an empty floppy 646drive for a couple of seconds, after which the system complains it 647can't read from it. Nowadays we can **sense** the existence of a 648removable medium in a drive, and we believe we should exploit that 649fact. An integrity check on opening of the device, that verifies the 650availability of a CD-ROM and its correct type (data), would be 651desirable. 652 653These two ways of using a CD-ROM drive, principally for data and 654secondarily for playing audio discs, have different demands for the 655behavior of the *open()* call. Audio use simply wants to open the 656device in order to get a file handle which is needed for issuing 657*ioctl* commands, while data use wants to open for correct and 658reliable data transfer. The only way user programs can indicate what 659their *purpose* of opening the device is, is through the *flags* 660parameter (see `open(2)`). For CD-ROM devices, these flags aren't 661implemented (some drivers implement checking for write-related flags, 662but this is not strictly necessary if the device file has correct 663permission flags). Most option flags simply don't make sense to 664CD-ROM devices: *O_CREAT*, *O_NOCTTY*, *O_TRUNC*, *O_APPEND*, and 665*O_SYNC* have no meaning to a CD-ROM. 666 667We therefore propose to use the flag *O_NONBLOCK* to indicate 668that the device is opened just for issuing *ioctl* 669commands. Strictly, the meaning of *O_NONBLOCK* is that opening and 670subsequent calls to the device don't cause the calling process to 671wait. We could interpret this as don't wait until someone has 672inserted some valid data-CD-ROM. Thus, our proposal of the 673implementation for the *open()* call for CD-ROM s is: 674 675- If no other flags are set than *O_RDONLY*, the device is opened 676 for data transfer, and the return value will be 0 only upon successful 677 initialization of the transfer. The call may even induce some actions 678 on the CD-ROM, such as closing the tray. 679- If the option flag *O_NONBLOCK* is set, opening will always be 680 successful, unless the whole device doesn't exist. The drive will take 681 no actions whatsoever. 682 683And what about standards? 684------------------------- 685 686You might hesitate to accept this proposal as it comes from the 687Linux community, and not from some standardizing institute. What 688about SUN, SGI, HP and all those other Unix and hardware vendors? 689Well, these companies are in the lucky position that they generally 690control both the hardware and software of their supported products, 691and are large enough to set their own standard. They do not have to 692deal with a dozen or more different, competing hardware 693configurations\ [#f3]_. 694 695.. [#f3] 696 697 Incidentally, I think that SUN's approach to mounting CD-ROM s is very 698 good in origin: under Solaris a volume-daemon automatically mounts a 699 newly inserted CD-ROM under `/cdrom/*<volume-name>*`. 700 701 In my opinion they should have pushed this 702 further and have **every** CD-ROM on the local area network be 703 mounted at the similar location, i. e., no matter in which particular 704 machine you insert a CD-ROM, it will always appear at the same 705 position in the directory tree, on every system. When I wanted to 706 implement such a user-program for Linux, I came across the 707 differences in behavior of the various drivers, and the need for an 708 *ioctl* informing about media changes. 709 710We believe that using *O_NONBLOCK* to indicate that a device is being opened 711for *ioctl* commands only can be easily introduced in the Linux 712community. All the CD-player authors will have to be informed, we can 713even send in our own patches to the programs. The use of *O_NONBLOCK* 714has most likely no influence on the behavior of the CD-players on 715other operating systems than Linux. Finally, a user can always revert 716to old behavior by a call to 717*ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, CDO_USE_FFLAGS)*. 718 719The preferred strategy of *open()* 720---------------------------------- 721 722The routines in `cdrom.c` are designed in such a way that run-time 723configuration of the behavior of CD-ROM devices (of **any** type) 724can be carried out, by the *CDROM_SET/CLEAR_OPTIONS* *ioctls*. Thus, various 725modes of operation can be set: 726 727`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK` 728 This is the default setting. (With *CDO_CHECK_TYPE* it will be better, in 729 the future.) If the device is not yet opened by any other process, and if 730 the device is being opened for data (*O_NONBLOCK* is not set) and the 731 tray is found to be open, an attempt to close the tray is made. Then, 732 it is verified that a disc is in the drive and, if *CDO_CHECK_TYPE* is 733 set, that it contains tracks of type `data mode 1`. Only if all tests 734 are passed is the return value zero. The door is locked to prevent file 735 system corruption. If the drive is opened for audio (*O_NONBLOCK* is 736 set), no actions are taken and a value of 0 will be returned. 737 738`CDO_AUTO_CLOSE | CDO_AUTO_EJECT | CDO_LOCK` 739 This mimics the behavior of the current sbpcd-driver. The option flags are 740 ignored, the tray is closed on the first open, if necessary. Similarly, 741 the tray is opened on the last release, i. e., if a CD-ROM is unmounted, 742 it is automatically ejected, such that the user can replace it. 743 744We hope that these option can convince everybody (both driver 745maintainers and user program developers) to adopt the new CD-ROM 746driver scheme and option flag interpretation. 747 748Description of routines in `cdrom.c` 749==================================== 750 751Only a few routines in `cdrom.c` are exported to the drivers. In this 752new section we will discuss these, as well as the functions that `take 753over' the CD-ROM interface to the kernel. The header file belonging 754to `cdrom.c` is called `cdrom.h`. Formerly, some of the contents of this 755file were placed in the file `ucdrom.h`, but this file has now been 756merged back into `cdrom.h`. 757 758:: 759 760 struct file_operations cdrom_fops 761 762The contents of this structure were described in cdrom_api_. 763A pointer to this structure is assigned to the *fops* field 764of the *struct gendisk*. 765 766:: 767 768 int register_cdrom(struct cdrom_device_info *cdi) 769 770This function is used in about the same way one registers *cdrom_fops* 771with the kernel, the device operations and information structures, 772as described in cdrom_api_, should be registered with the 773Uniform CD-ROM Driver:: 774 775 register_cdrom(&<device>_info); 776 777 778This function returns zero upon success, and non-zero upon 779failure. The structure *<device>_info* should have a pointer to the 780driver's *<device>_dops*, as in:: 781 782 struct cdrom_device_info <device>_info = { 783 <device>_dops; 784 ... 785 } 786 787Note that a driver must have one static structure, *<device>_dops*, while 788it may have as many structures *<device>_info* as there are minor devices 789active. *Register_cdrom()* builds a linked list from these. 790 791 792:: 793 794 void unregister_cdrom(struct cdrom_device_info *cdi) 795 796Unregistering device *cdi* with minor number *MINOR(cdi->dev)* removes 797the minor device from the list. If it was the last registered minor for 798the low-level driver, this disconnects the registered device-operation 799routines from the CD-ROM interface. This function returns zero upon 800success, and non-zero upon failure. 801 802:: 803 804 int cdrom_open(struct inode * ip, struct file * fp) 805 806This function is not called directly by the low-level drivers, it is 807listed in the standard *cdrom_fops*. If the VFS opens a file, this 808function becomes active. A strategy is implemented in this routine, 809taking care of all capabilities and options that are set in the 810*cdrom_device_ops* connected to the device. Then, the program flow is 811transferred to the device_dependent *open()* call. 812 813:: 814 815 void cdrom_release(struct inode *ip, struct file *fp) 816 817This function implements the reverse-logic of *cdrom_open()*, and then 818calls the device-dependent *release()* routine. When the use-count has 819reached 0, the allocated buffers are flushed by calls to *sync_dev(dev)* 820and *invalidate_buffers(dev)*. 821 822 823.. _cdrom_ioctl: 824 825:: 826 827 int cdrom_ioctl(struct inode *ip, struct file *fp, 828 unsigned int cmd, unsigned long arg) 829 830This function handles all the standard *ioctl* requests for CD-ROM 831devices in a uniform way. The different calls fall into three 832categories: *ioctl()'s* that can be directly implemented by device 833operations, ones that are routed through the call *audio_ioctl()*, and 834the remaining ones, that are presumable device-dependent. Generally, a 835negative return value indicates an error. 836 837Directly implemented *ioctl()'s* 838-------------------------------- 839 840The following `old` CD-ROM *ioctl()*\ 's are implemented by directly 841calling device-operations in *cdrom_device_ops*, if implemented and 842not masked: 843 844`CDROMMULTISESSION` 845 Requests the last session on a CD-ROM. 846`CDROMEJECT` 847 Open tray. 848`CDROMCLOSETRAY` 849 Close tray. 850`CDROMEJECT_SW` 851 If *arg\not=0*, set behavior to auto-close (close 852 tray on first open) and auto-eject (eject on last release), otherwise 853 set behavior to non-moving on *open()* and *release()* calls. 854`CDROM_GET_MCN` 855 Get the Media Catalog Number from a CD. 856 857*Ioctl*s routed through *audio_ioctl()* 858--------------------------------------- 859 860The following set of *ioctl()'s* are all implemented through a call to 861the *cdrom_fops* function *audio_ioctl()*. Memory checks and 862allocation are performed in *cdrom_ioctl()*, and also sanitization of 863address format (*CDROM_LBA*/*CDROM_MSF*) is done. 864 865`CDROMSUBCHNL` 866 Get sub-channel data in argument *arg* of type 867 `struct cdrom_subchnl *`. 868`CDROMREADTOCHDR` 869 Read Table of Contents header, in *arg* of type 870 `struct cdrom_tochdr *`. 871`CDROMREADTOCENTRY` 872 Read a Table of Contents entry in *arg* and specified by *arg* 873 of type `struct cdrom_tocentry *`. 874`CDROMPLAYMSF` 875 Play audio fragment specified in Minute, Second, Frame format, 876 delimited by *arg* of type `struct cdrom_msf *`. 877`CDROMPLAYTRKIND` 878 Play audio fragment in track-index format delimited by *arg* 879 of type `struct cdrom_ti *`. 880`CDROMVOLCTRL` 881 Set volume specified by *arg* of type `struct cdrom_volctrl *`. 882`CDROMVOLREAD` 883 Read volume into by *arg* of type `struct cdrom_volctrl *`. 884`CDROMSTART` 885 Spin up disc. 886`CDROMSTOP` 887 Stop playback of audio fragment. 888`CDROMPAUSE` 889 Pause playback of audio fragment. 890`CDROMRESUME` 891 Resume playing. 892 893New *ioctl()'s* in `cdrom.c` 894---------------------------- 895 896The following *ioctl()'s* have been introduced to allow user programs to 897control the behavior of individual CD-ROM devices. New *ioctl* 898commands can be identified by the underscores in their names. 899 900`CDROM_SET_OPTIONS` 901 Set options specified by *arg*. Returns the option flag register 902 after modification. Use *arg = \rm0* for reading the current flags. 903`CDROM_CLEAR_OPTIONS` 904 Clear options specified by *arg*. Returns the option flag register 905 after modification. 906`CDROM_SELECT_SPEED` 907 Select head-rate speed of disc specified as by *arg* in units 908 of standard cdrom speed (176\,kB/sec raw data or 909 150kB/sec file system data). The value 0 means `auto-select`, 910 i. e., play audio discs at real time and data discs at maximum speed. 911 The value *arg* is checked against the maximum head rate of the 912 drive found in the *cdrom_dops*. 913`CDROM_SELECT_DISC` 914 Select disc numbered *arg* from a juke-box. 915 916 First disc is numbered 0. The number *arg* is checked against the 917 maximum number of discs in the juke-box found in the *cdrom_dops*. 918`CDROM_MEDIA_CHANGED` 919 Returns 1 if a disc has been changed since the last call. 920 Note that calls to *cdrom_media_changed* by the VFS are treated 921 by an independent queue, so both mechanisms will detect a 922 media change once. For juke-boxes, an extra argument *arg* 923 specifies the slot for which the information is given. The special 924 value *CDSL_CURRENT* requests that information about the currently 925 selected slot be returned. 926`CDROM_DRIVE_STATUS` 927 Returns the status of the drive by a call to 928 *drive_status()*. Return values are defined in cdrom_drive_status_. 929 Note that this call doesn't return information on the 930 current playing activity of the drive; this can be polled through 931 an *ioctl* call to *CDROMSUBCHNL*. For juke-boxes, an extra argument 932 *arg* specifies the slot for which (possibly limited) information is 933 given. The special value *CDSL_CURRENT* requests that information 934 about the currently selected slot be returned. 935`CDROM_DISC_STATUS` 936 Returns the type of the disc currently in the drive. 937 It should be viewed as a complement to *CDROM_DRIVE_STATUS*. 938 This *ioctl* can provide *some* information about the current 939 disc that is inserted in the drive. This functionality used to be 940 implemented in the low level drivers, but is now carried out 941 entirely in Uniform CD-ROM Driver. 942 943 The history of development of the CD's use as a carrier medium for 944 various digital information has lead to many different disc types. 945 This *ioctl* is useful only in the case that CDs have \emph {only 946 one} type of data on them. While this is often the case, it is 947 also very common for CDs to have some tracks with data, and some 948 tracks with audio. Because this is an existing interface, rather 949 than fixing this interface by changing the assumptions it was made 950 under, thereby breaking all user applications that use this 951 function, the Uniform CD-ROM Driver implements this *ioctl* as 952 follows: If the CD in question has audio tracks on it, and it has 953 absolutely no CD-I, XA, or data tracks on it, it will be reported 954 as *CDS_AUDIO*. If it has both audio and data tracks, it will 955 return *CDS_MIXED*. If there are no audio tracks on the disc, and 956 if the CD in question has any CD-I tracks on it, it will be 957 reported as *CDS_XA_2_2*. Failing that, if the CD in question 958 has any XA tracks on it, it will be reported as *CDS_XA_2_1*. 959 Finally, if the CD in question has any data tracks on it, 960 it will be reported as a data CD (*CDS_DATA_1*). 961 962 This *ioctl* can return:: 963 964 CDS_NO_INFO /* no information available */ 965 CDS_NO_DISC /* no disc is inserted, or tray is opened */ 966 CDS_AUDIO /* Audio disc (2352 audio bytes/frame) */ 967 CDS_DATA_1 /* data disc, mode 1 (2048 user bytes/frame) */ 968 CDS_XA_2_1 /* mixed data (XA), mode 2, form 1 (2048 user bytes) */ 969 CDS_XA_2_2 /* mixed data (XA), mode 2, form 1 (2324 user bytes) */ 970 CDS_MIXED /* mixed audio/data disc */ 971 972 For some information concerning frame layout of the various disc 973 types, see a recent version of `cdrom.h`. 974 975`CDROM_CHANGER_NSLOTS` 976 Returns the number of slots in a juke-box. 977`CDROMRESET` 978 Reset the drive. 979`CDROM_GET_CAPABILITY` 980 Returns the *capability* flags for the drive. Refer to section 981 cdrom_capabilities_ for more information on these flags. 982`CDROM_LOCKDOOR` 983 Locks the door of the drive. `arg == 0` unlocks the door, 984 any other value locks it. 985`CDROM_DEBUG` 986 Turns on debugging info. Only root is allowed to do this. 987 Same semantics as CDROM_LOCKDOOR. 988 989 990Device dependent *ioctl()'s* 991---------------------------- 992 993Finally, all other *ioctl()'s* are passed to the function *dev_ioctl()*, 994if implemented. No memory allocation or verification is carried out. 995 996How to update your driver 997========================= 998 999- Make a backup of your current driver. 1000- Get hold of the files `cdrom.c` and `cdrom.h`, they should be in 1001 the directory tree that came with this documentation. 1002- Make sure you include `cdrom.h`. 1003- Change the 3rd argument of *register_blkdev* from `&<your-drive>_fops` 1004 to `&cdrom_fops`. 1005- Just after that line, add the following to register with the Uniform 1006 CD-ROM Driver:: 1007 1008 register_cdrom(&<your-drive>_info);* 1009 1010 Similarly, add a call to *unregister_cdrom()* at the appropriate place. 1011- Copy an example of the device-operations *struct* to your 1012 source, e. g., from `cm206.c` *cm206_dops*, and change all 1013 entries to names corresponding to your driver, or names you just 1014 happen to like. If your driver doesn't support a certain function, 1015 make the entry *NULL*. At the entry *capability* you should list all 1016 capabilities your driver currently supports. If your driver 1017 has a capability that is not listed, please send me a message. 1018- Copy the *cdrom_device_info* declaration from the same example 1019 driver, and modify the entries according to your needs. If your 1020 driver dynamically determines the capabilities of the hardware, this 1021 structure should also be declared dynamically. 1022- Implement all functions in your `<device>_dops` structure, 1023 according to prototypes listed in `cdrom.h`, and specifications given 1024 in cdrom_api_. Most likely you have already implemented 1025 the code in a large part, and you will almost certainly need to adapt the 1026 prototype and return values. 1027- Rename your `<device>_ioctl()` function to *audio_ioctl* and 1028 change the prototype a little. Remove entries listed in the first 1029 part in cdrom_ioctl_, if your code was OK, these are 1030 just calls to the routines you adapted in the previous step. 1031- You may remove all remaining memory checking code in the 1032 *audio_ioctl()* function that deals with audio commands (these are 1033 listed in the second part of cdrom_ioctl_. There is no 1034 need for memory allocation either, so most *case*s in the *switch* 1035 statement look similar to:: 1036 1037 case CDROMREADTOCENTRY: 1038 get_toc_entry\bigl((struct cdrom_tocentry *) arg); 1039 1040- All remaining *ioctl* cases must be moved to a separate 1041 function, *<device>_ioctl*, the device-dependent *ioctl()'s*. Note that 1042 memory checking and allocation must be kept in this code! 1043- Change the prototypes of *<device>_open()* and 1044 *<device>_release()*, and remove any strategic code (i. e., tray 1045 movement, door locking, etc.). 1046- Try to recompile the drivers. We advise you to use modules, both 1047 for `cdrom.o` and your driver, as debugging is much easier this 1048 way. 1049 1050Thanks 1051====== 1052 1053Thanks to all the people involved. First, Erik Andersen, who has 1054taken over the torch in maintaining `cdrom.c` and integrating much 1055CD-ROM-related code in the 2.1-kernel. Thanks to Scott Snyder and 1056Gerd Knorr, who were the first to implement this interface for SCSI 1057and IDE-CD drivers and added many ideas for extension of the data 1058structures relative to kernel~2.0. Further thanks to Heiko Eißfeldt, 1059Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard Mönkeberg and Andrew Kroll, 1060the Linux CD-ROM device driver developers who were kind 1061enough to give suggestions and criticisms during the writing. Finally 1062of course, I want to thank Linus Torvalds for making this possible in 1063the first place. 1064