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 NULL /* revalidate */ 161 }; 162 163Every active CD-ROM device shares this *struct*. The routines 164declared above are all implemented in `cdrom.c`, since this file is the 165place where the behavior of all CD-ROM-devices is defined and 166standardized. The actual interface to the various types of CD-ROM 167hardware is still performed by various low-level CD-ROM-device 168drivers. These routines simply implement certain **capabilities** 169that are common to all CD-ROM (and really, all removable-media 170devices). 171 172Registration of a low-level CD-ROM device driver is now done through 173the general routines in `cdrom.c`, not through the Virtual File System 174(VFS) any more. The interface implemented in `cdrom.c` is carried out 175through two general structures that contain information about the 176capabilities of the driver, and the specific drives on which the 177driver operates. The structures are: 178 179cdrom_device_ops 180 This structure contains information about the low-level driver for a 181 CD-ROM device. This structure is conceptually connected to the major 182 number of the device (although some drivers may have different 183 major numbers, as is the case for the IDE driver). 184 185cdrom_device_info 186 This structure contains information about a particular CD-ROM drive, 187 such as its device name, speed, etc. This structure is conceptually 188 connected to the minor number of the device. 189 190Registering a particular CD-ROM drive with the Uniform CD-ROM Driver 191is done by the low-level device driver though a call to:: 192 193 register_cdrom(struct cdrom_device_info * <device>_info) 194 195The device information structure, *<device>_info*, contains all the 196information needed for the kernel to interface with the low-level 197CD-ROM device driver. One of the most important entries in this 198structure is a pointer to the *cdrom_device_ops* structure of the 199low-level driver. 200 201The device operations structure, *cdrom_device_ops*, contains a list 202of pointers to the functions which are implemented in the low-level 203device driver. When `cdrom.c` accesses a CD-ROM device, it does it 204through the functions in this structure. It is impossible to know all 205the capabilities of future CD-ROM drives, so it is expected that this 206list may need to be expanded from time to time as new technologies are 207developed. For example, CD-R and CD-R/W drives are beginning to become 208popular, and support will soon need to be added for them. For now, the 209current *struct* is:: 210 211 struct cdrom_device_ops { 212 int (*open)(struct cdrom_device_info *, int) 213 void (*release)(struct cdrom_device_info *); 214 int (*drive_status)(struct cdrom_device_info *, int); 215 unsigned int (*check_events)(struct cdrom_device_info *, 216 unsigned int, int); 217 int (*media_changed)(struct cdrom_device_info *, int); 218 int (*tray_move)(struct cdrom_device_info *, int); 219 int (*lock_door)(struct cdrom_device_info *, int); 220 int (*select_speed)(struct cdrom_device_info *, int); 221 int (*get_last_session) (struct cdrom_device_info *, 222 struct cdrom_multisession *); 223 int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *); 224 int (*reset)(struct cdrom_device_info *); 225 int (*audio_ioctl)(struct cdrom_device_info *, 226 unsigned int, void *); 227 const int capability; /* capability flags */ 228 int (*generic_packet)(struct cdrom_device_info *, 229 struct packet_command *); 230 }; 231 232When a low-level device driver implements one of these capabilities, 233it should add a function pointer to this *struct*. When a particular 234function is not implemented, however, this *struct* should contain a 235NULL instead. The *capability* flags specify the capabilities of the 236CD-ROM hardware and/or low-level CD-ROM driver when a CD-ROM drive 237is registered with the Uniform CD-ROM Driver. 238 239Note that most functions have fewer parameters than their 240*blkdev_fops* counterparts. This is because very little of the 241information in the structures *inode* and *file* is used. For most 242drivers, the main parameter is the *struct* *cdrom_device_info*, from 243which the major and minor number can be extracted. (Most low-level 244CD-ROM drivers don't even look at the major and minor number though, 245since many of them only support one device.) This will be available 246through *dev* in *cdrom_device_info* described below. 247 248The drive-specific, minor-like information that is registered with 249`cdrom.c`, currently contains the following fields:: 250 251 struct cdrom_device_info { 252 const struct cdrom_device_ops * ops; /* device operations for this major */ 253 struct list_head list; /* linked list of all device_info */ 254 struct gendisk * disk; /* matching block layer disk */ 255 void * handle; /* driver-dependent data */ 256 257 int mask; /* mask of capability: disables them */ 258 int speed; /* maximum speed for reading data */ 259 int capacity; /* number of discs in a jukebox */ 260 261 unsigned int options:30; /* options flags */ 262 unsigned mc_flags:2; /* media-change buffer flags */ 263 unsigned int vfs_events; /* cached events for vfs path */ 264 unsigned int ioctl_events; /* cached events for ioctl path */ 265 int use_count; /* number of times device is opened */ 266 char name[20]; /* name of the device type */ 267 268 __u8 sanyo_slot : 2; /* Sanyo 3-CD changer support */ 269 __u8 keeplocked : 1; /* CDROM_LOCKDOOR status */ 270 __u8 reserved : 5; /* not used yet */ 271 int cdda_method; /* see CDDA_* flags */ 272 __u8 last_sense; /* saves last sense key */ 273 __u8 media_written; /* dirty flag, DVD+RW bookkeeping */ 274 unsigned short mmc3_profile; /* current MMC3 profile */ 275 int for_data; /* unknown:TBD */ 276 int (*exit)(struct cdrom_device_info *);/* unknown:TBD */ 277 int mrw_mode_page; /* which MRW mode page is in use */ 278 }; 279 280Using this *struct*, a linked list of the registered minor devices is 281built, using the *next* field. The device number, the device operations 282struct and specifications of properties of the drive are stored in this 283structure. 284 285The *mask* flags can be used to mask out some of the capabilities listed 286in *ops->capability*, if a specific drive doesn't support a feature 287of the driver. The value *speed* specifies the maximum head-rate of the 288drive, measured in units of normal audio speed (176kB/sec raw data or 289150kB/sec file system data). The parameters are declared *const* 290because they describe properties of the drive, which don't change after 291registration. 292 293A few registers contain variables local to the CD-ROM drive. The 294flags *options* are used to specify how the general CD-ROM routines 295should behave. These various flags registers should provide enough 296flexibility to adapt to the different users' wishes (and **not** the 297`arbitrary` wishes of the author of the low-level device driver, as is 298the case in the old scheme). The register *mc_flags* is used to buffer 299the information from *media_changed()* to two separate queues. Other 300data that is specific to a minor drive, can be accessed through *handle*, 301which can point to a data structure specific to the low-level driver. 302The fields *use_count*, *next*, *options* and *mc_flags* need not be 303initialized. 304 305The intermediate software layer that `cdrom.c` forms will perform some 306additional bookkeeping. The use count of the device (the number of 307processes that have the device opened) is registered in *use_count*. The 308function *cdrom_ioctl()* will verify the appropriate user-memory regions 309for read and write, and in case a location on the CD is transferred, 310it will `sanitize` the format by making requests to the low-level 311drivers in a standard format, and translating all formats between the 312user-software and low level drivers. This relieves much of the drivers' 313memory checking and format checking and translation. Also, the necessary 314structures will be declared on the program stack. 315 316The implementation of the functions should be as defined in the 317following sections. Two functions **must** be implemented, namely 318*open()* and *release()*. Other functions may be omitted, their 319corresponding capability flags will be cleared upon registration. 320Generally, a function returns zero on success and negative on error. A 321function call should return only after the command has completed, but of 322course waiting for the device should not use processor time. 323 324:: 325 326 int open(struct cdrom_device_info *cdi, int purpose) 327 328*Open()* should try to open the device for a specific *purpose*, which 329can be either: 330 331- Open for reading data, as done by `mount()` (2), or the 332 user commands `dd` or `cat`. 333- Open for *ioctl* commands, as done by audio-CD playing programs. 334 335Notice that any strategic code (closing tray upon *open()*, etc.) is 336done by the calling routine in `cdrom.c`, so the low-level routine 337should only be concerned with proper initialization, such as spinning 338up the disc, etc. 339 340:: 341 342 void release(struct cdrom_device_info *cdi) 343 344Device-specific actions should be taken such as spinning down the device. 345However, strategic actions such as ejection of the tray, or unlocking 346the door, should be left over to the general routine *cdrom_release()*. 347This is the only function returning type *void*. 348 349.. _cdrom_drive_status: 350 351:: 352 353 int drive_status(struct cdrom_device_info *cdi, int slot_nr) 354 355The function *drive_status*, if implemented, should provide 356information on the status of the drive (not the status of the disc, 357which may or may not be in the drive). If the drive is not a changer, 358*slot_nr* should be ignored. In `cdrom.h` the possibilities are listed:: 359 360 361 CDS_NO_INFO /* no information available */ 362 CDS_NO_DISC /* no disc is inserted, tray is closed */ 363 CDS_TRAY_OPEN /* tray is opened */ 364 CDS_DRIVE_NOT_READY /* something is wrong, tray is moving? */ 365 CDS_DISC_OK /* a disc is loaded and everything is fine */ 366 367:: 368 369 int tray_move(struct cdrom_device_info *cdi, int position) 370 371This function, if implemented, should control the tray movement. (No 372other function should control this.) The parameter *position* controls 373the desired direction of movement: 374 375- 0 Close tray 376- 1 Open tray 377 378This function returns 0 upon success, and a non-zero value upon 379error. Note that if the tray is already in the desired position, no 380action need be taken, and the return value should be 0. 381 382:: 383 384 int lock_door(struct cdrom_device_info *cdi, int lock) 385 386This function (and no other code) controls locking of the door, if the 387drive allows this. The value of *lock* controls the desired locking 388state: 389 390- 0 Unlock door, manual opening is allowed 391- 1 Lock door, tray cannot be ejected manually 392 393This function returns 0 upon success, and a non-zero value upon 394error. Note that if the door is already in the requested state, no 395action need be taken, and the return value should be 0. 396 397:: 398 399 int select_speed(struct cdrom_device_info *cdi, int speed) 400 401Some CD-ROM drives are capable of changing their head-speed. There 402are several reasons for changing the speed of a CD-ROM drive. Badly 403pressed CD-ROM s may benefit from less-than-maximum head rate. Modern 404CD-ROM drives can obtain very high head rates (up to *24x* is 405common). It has been reported that these drives can make reading 406errors at these high speeds, reducing the speed can prevent data loss 407in these circumstances. Finally, some of these drives can 408make an annoyingly loud noise, which a lower speed may reduce. 409 410This function specifies the speed at which data is read or audio is 411played back. The value of *speed* specifies the head-speed of the 412drive, measured in units of standard cdrom speed (176kB/sec raw data 413or 150kB/sec file system data). So to request that a CD-ROM drive 414operate at 300kB/sec you would call the CDROM_SELECT_SPEED *ioctl* 415with *speed=2*. The special value `0` means `auto-selection`, i. e., 416maximum data-rate or real-time audio rate. If the drive doesn't have 417this `auto-selection` capability, the decision should be made on the 418current disc loaded and the return value should be positive. A negative 419return value indicates an error. 420 421:: 422 423 int get_last_session(struct cdrom_device_info *cdi, 424 struct cdrom_multisession *ms_info) 425 426This function should implement the old corresponding *ioctl()*. For 427device *cdi->dev*, the start of the last session of the current disc 428should be returned in the pointer argument *ms_info*. Note that 429routines in `cdrom.c` have sanitized this argument: its requested 430format will **always** be of the type *CDROM_LBA* (linear block 431addressing mode), whatever the calling software requested. But 432sanitization goes even further: the low-level implementation may 433return the requested information in *CDROM_MSF* format if it wishes so 434(setting the *ms_info->addr_format* field appropriately, of 435course) and the routines in `cdrom.c` will make the transformation if 436necessary. The return value is 0 upon success. 437 438:: 439 440 int get_mcn(struct cdrom_device_info *cdi, 441 struct cdrom_mcn *mcn) 442 443Some discs carry a `Media Catalog Number` (MCN), also called 444`Universal Product Code` (UPC). This number should reflect the number 445that is generally found in the bar-code on the product. Unfortunately, 446the few discs that carry such a number on the disc don't even use the 447same format. The return argument to this function is a pointer to a 448pre-declared memory region of type *struct cdrom_mcn*. The MCN is 449expected as a 13-character string, terminated by a null-character. 450 451:: 452 453 int reset(struct cdrom_device_info *cdi) 454 455This call should perform a hard-reset on the drive (although in 456circumstances that a hard-reset is necessary, a drive may very well not 457listen to commands anymore). Preferably, control is returned to the 458caller only after the drive has finished resetting. If the drive is no 459longer listening, it may be wise for the underlying low-level cdrom 460driver to time out. 461 462:: 463 464 int audio_ioctl(struct cdrom_device_info *cdi, 465 unsigned int cmd, void *arg) 466 467Some of the CD-ROM-\ *ioctl()*\ 's defined in `cdrom.h` can be 468implemented by the routines described above, and hence the function 469*cdrom_ioctl* will use those. However, most *ioctl()*\ 's deal with 470audio-control. We have decided to leave these to be accessed through a 471single function, repeating the arguments *cmd* and *arg*. Note that 472the latter is of type *void*, rather than *unsigned long int*. 473The routine *cdrom_ioctl()* does do some useful things, 474though. It sanitizes the address format type to *CDROM_MSF* (Minutes, 475Seconds, Frames) for all audio calls. It also verifies the memory 476location of *arg*, and reserves stack-memory for the argument. This 477makes implementation of the *audio_ioctl()* much simpler than in the 478old driver scheme. For example, you may look up the function 479*cm206_audio_ioctl()* `cm206.c` that should be updated with 480this documentation. 481 482An unimplemented ioctl should return *-ENOSYS*, but a harmless request 483(e. g., *CDROMSTART*) may be ignored by returning 0 (success). Other 484errors should be according to the standards, whatever they are. When 485an error is returned by the low-level driver, the Uniform CD-ROM Driver 486tries whenever possible to return the error code to the calling program. 487(We may decide to sanitize the return value in *cdrom_ioctl()* though, in 488order to guarantee a uniform interface to the audio-player software.) 489 490:: 491 492 int dev_ioctl(struct cdrom_device_info *cdi, 493 unsigned int cmd, unsigned long arg) 494 495Some *ioctl()'s* seem to be specific to certain CD-ROM drives. That is, 496they are introduced to service some capabilities of certain drives. In 497fact, there are 6 different *ioctl()'s* for reading data, either in some 498particular kind of format, or audio data. Not many drives support 499reading audio tracks as data, I believe this is because of protection 500of copyrights of artists. Moreover, I think that if audio-tracks are 501supported, it should be done through the VFS and not via *ioctl()'s*. A 502problem here could be the fact that audio-frames are 2352 bytes long, 503so either the audio-file-system should ask for 75264 bytes at once 504(the least common multiple of 512 and 2352), or the drivers should 505bend their backs to cope with this incoherence (to which I would be 506opposed). Furthermore, it is very difficult for the hardware to find 507the exact frame boundaries, since there are no synchronization headers 508in audio frames. Once these issues are resolved, this code should be 509standardized in `cdrom.c`. 510 511Because there are so many *ioctl()'s* that seem to be introduced to 512satisfy certain drivers [#f2]_, any non-standard *ioctl()*\ s 513are routed through the call *dev_ioctl()*. In principle, `private` 514*ioctl()*\ 's should be numbered after the device's major number, and not 515the general CD-ROM *ioctl* number, `0x53`. Currently the 516non-supported *ioctl()'s* are: 517 518 CDROMREADMODE1, CDROMREADMODE2, CDROMREADAUDIO, CDROMREADRAW, 519 CDROMREADCOOKED, CDROMSEEK, CDROMPLAY-BLK and CDROM-READALL 520 521.. [#f2] 522 523 Is there software around that actually uses these? I'd be interested! 524 525.. _cdrom_capabilities: 526 527CD-ROM capabilities 528------------------- 529 530Instead of just implementing some *ioctl* calls, the interface in 531`cdrom.c` supplies the possibility to indicate the **capabilities** 532of a CD-ROM drive. This can be done by ORing any number of 533capability-constants that are defined in `cdrom.h` at the registration 534phase. Currently, the capabilities are any of:: 535 536 CDC_CLOSE_TRAY /* can close tray by software control */ 537 CDC_OPEN_TRAY /* can open tray */ 538 CDC_LOCK /* can lock and unlock the door */ 539 CDC_SELECT_SPEED /* can select speed, in units of * sim*150 ,kB/s */ 540 CDC_SELECT_DISC /* drive is juke-box */ 541 CDC_MULTI_SESSION /* can read sessions *> rm1* */ 542 CDC_MCN /* can read Media Catalog Number */ 543 CDC_MEDIA_CHANGED /* can report if disc has changed */ 544 CDC_PLAY_AUDIO /* can perform audio-functions (play, pause, etc) */ 545 CDC_RESET /* hard reset device */ 546 CDC_IOCTLS /* driver has non-standard ioctls */ 547 CDC_DRIVE_STATUS /* driver implements drive status */ 548 549The capability flag is declared *const*, to prevent drivers from 550accidentally tampering with the contents. The capability flags actually 551inform `cdrom.c` of what the driver can do. If the drive found 552by the driver does not have the capability, is can be masked out by 553the *cdrom_device_info* variable *mask*. For instance, the SCSI CD-ROM 554driver has implemented the code for loading and ejecting CD-ROM's, and 555hence its corresponding flags in *capability* will be set. But a SCSI 556CD-ROM drive might be a caddy system, which can't load the tray, and 557hence for this drive the *cdrom_device_info* struct will have set 558the *CDC_CLOSE_TRAY* bit in *mask*. 559 560In the file `cdrom.c` you will encounter many constructions of the type:: 561 562 if (cdo->capability & ~cdi->mask & CDC _<capability>) ... 563 564There is no *ioctl* to set the mask... The reason is that 565I think it is better to control the **behavior** rather than the 566**capabilities**. 567 568Options 569------- 570 571A final flag register controls the **behavior** of the CD-ROM 572drives, in order to satisfy different users' wishes, hopefully 573independently of the ideas of the respective author who happened to 574have made the drive's support available to the Linux community. The 575current behavior options are:: 576 577 CDO_AUTO_CLOSE /* try to close tray upon device open() */ 578 CDO_AUTO_EJECT /* try to open tray on last device close() */ 579 CDO_USE_FFLAGS /* use file_pointer->f_flags to indicate purpose for open() */ 580 CDO_LOCK /* try to lock door if device is opened */ 581 CDO_CHECK_TYPE /* ensure disc type is data if opened for data */ 582 583The initial value of this register is 584`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK`, reflecting my own view on user 585interface and software standards. Before you protest, there are two 586new *ioctl()'s* implemented in `cdrom.c`, that allow you to control the 587behavior by software. These are:: 588 589 CDROM_SET_OPTIONS /* set options specified in (int)arg */ 590 CDROM_CLEAR_OPTIONS /* clear options specified in (int)arg */ 591 592One option needs some more explanation: *CDO_USE_FFLAGS*. In the next 593newsection we explain what the need for this option is. 594 595A software package `setcd`, available from the Debian distribution 596and `sunsite.unc.edu`, allows user level control of these flags. 597 598 599The need to know the purpose of opening the CD-ROM device 600========================================================= 601 602Traditionally, Unix devices can be used in two different `modes`, 603either by reading/writing to the device file, or by issuing 604controlling commands to the device, by the device's *ioctl()* 605call. The problem with CD-ROM drives, is that they can be used for 606two entirely different purposes. One is to mount removable 607file systems, CD-ROM's, the other is to play audio CD's. Audio commands 608are implemented entirely through *ioctl()\'s*, presumably because the 609first implementation (SUN?) has been such. In principle there is 610nothing wrong with this, but a good control of the `CD player` demands 611that the device can **always** be opened in order to give the 612*ioctl* commands, regardless of the state the drive is in. 613 614On the other hand, when used as a removable-media disc drive (what the 615original purpose of CD-ROM s is) we would like to make sure that the 616disc drive is ready for operation upon opening the device. In the old 617scheme, some CD-ROM drivers don't do any integrity checking, resulting 618in a number of i/o errors reported by the VFS to the kernel when an 619attempt for mounting a CD-ROM on an empty drive occurs. This is not a 620particularly elegant way to find out that there is no CD-ROM inserted; 621it more-or-less looks like the old IBM-PC trying to read an empty floppy 622drive for a couple of seconds, after which the system complains it 623can't read from it. Nowadays we can **sense** the existence of a 624removable medium in a drive, and we believe we should exploit that 625fact. An integrity check on opening of the device, that verifies the 626availability of a CD-ROM and its correct type (data), would be 627desirable. 628 629These two ways of using a CD-ROM drive, principally for data and 630secondarily for playing audio discs, have different demands for the 631behavior of the *open()* call. Audio use simply wants to open the 632device in order to get a file handle which is needed for issuing 633*ioctl* commands, while data use wants to open for correct and 634reliable data transfer. The only way user programs can indicate what 635their *purpose* of opening the device is, is through the *flags* 636parameter (see `open(2)`). For CD-ROM devices, these flags aren't 637implemented (some drivers implement checking for write-related flags, 638but this is not strictly necessary if the device file has correct 639permission flags). Most option flags simply don't make sense to 640CD-ROM devices: *O_CREAT*, *O_NOCTTY*, *O_TRUNC*, *O_APPEND*, and 641*O_SYNC* have no meaning to a CD-ROM. 642 643We therefore propose to use the flag *O_NONBLOCK* to indicate 644that the device is opened just for issuing *ioctl* 645commands. Strictly, the meaning of *O_NONBLOCK* is that opening and 646subsequent calls to the device don't cause the calling process to 647wait. We could interpret this as don't wait until someone has 648inserted some valid data-CD-ROM. Thus, our proposal of the 649implementation for the *open()* call for CD-ROM s is: 650 651- If no other flags are set than *O_RDONLY*, the device is opened 652 for data transfer, and the return value will be 0 only upon successful 653 initialization of the transfer. The call may even induce some actions 654 on the CD-ROM, such as closing the tray. 655- If the option flag *O_NONBLOCK* is set, opening will always be 656 successful, unless the whole device doesn't exist. The drive will take 657 no actions whatsoever. 658 659And what about standards? 660------------------------- 661 662You might hesitate to accept this proposal as it comes from the 663Linux community, and not from some standardizing institute. What 664about SUN, SGI, HP and all those other Unix and hardware vendors? 665Well, these companies are in the lucky position that they generally 666control both the hardware and software of their supported products, 667and are large enough to set their own standard. They do not have to 668deal with a dozen or more different, competing hardware 669configurations\ [#f3]_. 670 671.. [#f3] 672 673 Incidentally, I think that SUN's approach to mounting CD-ROM s is very 674 good in origin: under Solaris a volume-daemon automatically mounts a 675 newly inserted CD-ROM under `/cdrom/*<volume-name>*`. 676 677 In my opinion they should have pushed this 678 further and have **every** CD-ROM on the local area network be 679 mounted at the similar location, i. e., no matter in which particular 680 machine you insert a CD-ROM, it will always appear at the same 681 position in the directory tree, on every system. When I wanted to 682 implement such a user-program for Linux, I came across the 683 differences in behavior of the various drivers, and the need for an 684 *ioctl* informing about media changes. 685 686We believe that using *O_NONBLOCK* to indicate that a device is being opened 687for *ioctl* commands only can be easily introduced in the Linux 688community. All the CD-player authors will have to be informed, we can 689even send in our own patches to the programs. The use of *O_NONBLOCK* 690has most likely no influence on the behavior of the CD-players on 691other operating systems than Linux. Finally, a user can always revert 692to old behavior by a call to 693*ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, CDO_USE_FFLAGS)*. 694 695The preferred strategy of *open()* 696---------------------------------- 697 698The routines in `cdrom.c` are designed in such a way that run-time 699configuration of the behavior of CD-ROM devices (of **any** type) 700can be carried out, by the *CDROM_SET/CLEAR_OPTIONS* *ioctls*. Thus, various 701modes of operation can be set: 702 703`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK` 704 This is the default setting. (With *CDO_CHECK_TYPE* it will be better, in 705 the future.) If the device is not yet opened by any other process, and if 706 the device is being opened for data (*O_NONBLOCK* is not set) and the 707 tray is found to be open, an attempt to close the tray is made. Then, 708 it is verified that a disc is in the drive and, if *CDO_CHECK_TYPE* is 709 set, that it contains tracks of type `data mode 1`. Only if all tests 710 are passed is the return value zero. The door is locked to prevent file 711 system corruption. If the drive is opened for audio (*O_NONBLOCK* is 712 set), no actions are taken and a value of 0 will be returned. 713 714`CDO_AUTO_CLOSE | CDO_AUTO_EJECT | CDO_LOCK` 715 This mimics the behavior of the current sbpcd-driver. The option flags are 716 ignored, the tray is closed on the first open, if necessary. Similarly, 717 the tray is opened on the last release, i. e., if a CD-ROM is unmounted, 718 it is automatically ejected, such that the user can replace it. 719 720We hope that these option can convince everybody (both driver 721maintainers and user program developers) to adopt the new CD-ROM 722driver scheme and option flag interpretation. 723 724Description of routines in `cdrom.c` 725==================================== 726 727Only a few routines in `cdrom.c` are exported to the drivers. In this 728new section we will discuss these, as well as the functions that `take 729over` the CD-ROM interface to the kernel. The header file belonging 730to `cdrom.c` is called `cdrom.h`. Formerly, some of the contents of this 731file were placed in the file `ucdrom.h`, but this file has now been 732merged back into `cdrom.h`. 733 734:: 735 736 struct file_operations cdrom_fops 737 738The contents of this structure were described in cdrom_api_. 739A pointer to this structure is assigned to the *fops* field 740of the *struct gendisk*. 741 742:: 743 744 int register_cdrom(struct cdrom_device_info *cdi) 745 746This function is used in about the same way one registers *cdrom_fops* 747with the kernel, the device operations and information structures, 748as described in cdrom_api_, should be registered with the 749Uniform CD-ROM Driver:: 750 751 register_cdrom(&<device>_info); 752 753 754This function returns zero upon success, and non-zero upon 755failure. The structure *<device>_info* should have a pointer to the 756driver's *<device>_dops*, as in:: 757 758 struct cdrom_device_info <device>_info = { 759 <device>_dops; 760 ... 761 } 762 763Note that a driver must have one static structure, *<device>_dops*, while 764it may have as many structures *<device>_info* as there are minor devices 765active. *Register_cdrom()* builds a linked list from these. 766 767 768:: 769 770 void unregister_cdrom(struct cdrom_device_info *cdi) 771 772Unregistering device *cdi* with minor number *MINOR(cdi->dev)* removes 773the minor device from the list. If it was the last registered minor for 774the low-level driver, this disconnects the registered device-operation 775routines from the CD-ROM interface. This function returns zero upon 776success, and non-zero upon failure. 777 778:: 779 780 int cdrom_open(struct inode * ip, struct file * fp) 781 782This function is not called directly by the low-level drivers, it is 783listed in the standard *cdrom_fops*. If the VFS opens a file, this 784function becomes active. A strategy is implemented in this routine, 785taking care of all capabilities and options that are set in the 786*cdrom_device_ops* connected to the device. Then, the program flow is 787transferred to the device_dependent *open()* call. 788 789:: 790 791 void cdrom_release(struct inode *ip, struct file *fp) 792 793This function implements the reverse-logic of *cdrom_open()*, and then 794calls the device-dependent *release()* routine. When the use-count has 795reached 0, the allocated buffers are flushed by calls to *sync_dev(dev)* 796and *invalidate_buffers(dev)*. 797 798 799.. _cdrom_ioctl: 800 801:: 802 803 int cdrom_ioctl(struct inode *ip, struct file *fp, 804 unsigned int cmd, unsigned long arg) 805 806This function handles all the standard *ioctl* requests for CD-ROM 807devices in a uniform way. The different calls fall into three 808categories: *ioctl()'s* that can be directly implemented by device 809operations, ones that are routed through the call *audio_ioctl()*, and 810the remaining ones, that are presumable device-dependent. Generally, a 811negative return value indicates an error. 812 813Directly implemented *ioctl()'s* 814-------------------------------- 815 816The following `old` CD-ROM *ioctl()*\ 's are implemented by directly 817calling device-operations in *cdrom_device_ops*, if implemented and 818not masked: 819 820`CDROMMULTISESSION` 821 Requests the last session on a CD-ROM. 822`CDROMEJECT` 823 Open tray. 824`CDROMCLOSETRAY` 825 Close tray. 826`CDROMEJECT_SW` 827 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`CDROM_GET_MCN` 831 Get the Media Catalog Number from a CD. 832 833*Ioctl*s routed through *audio_ioctl()* 834--------------------------------------- 835 836The following set of *ioctl()'s* are all implemented through a call to 837the *cdrom_fops* function *audio_ioctl()*. Memory checks and 838allocation are performed in *cdrom_ioctl()*, and also sanitization of 839address format (*CDROM_LBA*/*CDROM_MSF*) is done. 840 841`CDROMSUBCHNL` 842 Get sub-channel data in argument *arg* of type 843 `struct cdrom_subchnl *`. 844`CDROMREADTOCHDR` 845 Read Table of Contents header, in *arg* of type 846 `struct cdrom_tochdr *`. 847`CDROMREADTOCENTRY` 848 Read a Table of Contents entry in *arg* and specified by *arg* 849 of type `struct cdrom_tocentry *`. 850`CDROMPLAYMSF` 851 Play audio fragment specified in Minute, Second, Frame format, 852 delimited by *arg* of type `struct cdrom_msf *`. 853`CDROMPLAYTRKIND` 854 Play audio fragment in track-index format delimited by *arg* 855 of type `struct cdrom_ti *`. 856`CDROMVOLCTRL` 857 Set volume specified by *arg* of type `struct cdrom_volctrl *`. 858`CDROMVOLREAD` 859 Read volume into by *arg* of type `struct cdrom_volctrl *`. 860`CDROMSTART` 861 Spin up disc. 862`CDROMSTOP` 863 Stop playback of audio fragment. 864`CDROMPAUSE` 865 Pause playback of audio fragment. 866`CDROMRESUME` 867 Resume playing. 868 869New *ioctl()'s* in `cdrom.c` 870---------------------------- 871 872The following *ioctl()'s* have been introduced to allow user programs to 873control the behavior of individual CD-ROM devices. New *ioctl* 874commands can be identified by the underscores in their names. 875 876`CDROM_SET_OPTIONS` 877 Set options specified by *arg*. Returns the option flag register 878 after modification. Use *arg = \rm0* for reading the current flags. 879`CDROM_CLEAR_OPTIONS` 880 Clear options specified by *arg*. Returns the option flag register 881 after modification. 882`CDROM_SELECT_SPEED` 883 Select head-rate speed of disc specified as by *arg* in units 884 of standard cdrom speed (176\,kB/sec raw data or 885 150kB/sec file system data). The value 0 means `auto-select`, 886 i. e., play audio discs at real time and data discs at maximum speed. 887 The value *arg* is checked against the maximum head rate of the 888 drive found in the *cdrom_dops*. 889`CDROM_SELECT_DISC` 890 Select disc numbered *arg* from a juke-box. 891 892 First disc is numbered 0. The number *arg* is checked against the 893 maximum number of discs in the juke-box found in the *cdrom_dops*. 894`CDROM_MEDIA_CHANGED` 895 Returns 1 if a disc has been changed since the last call. 896 For juke-boxes, an extra argument *arg* 897 specifies the slot for which the information is given. The special 898 value *CDSL_CURRENT* requests that information about the currently 899 selected slot be returned. 900`CDROM_TIMED_MEDIA_CHANGE` 901 Checks whether the disc has been changed since a user supplied time 902 and returns the time of the last disc change. 903 904 *arg* is a pointer to a *cdrom_timed_media_change_info* struct. 905 *arg->last_media_change* may be set by calling code to signal 906 the timestamp of the last known media change (by the caller). 907 Upon successful return, this ioctl call will set 908 *arg->last_media_change* to the latest media change timestamp (in ms) 909 known by the kernel/driver and set *arg->has_changed* to 1 if 910 that timestamp is more recent than the timestamp set by the caller. 911`CDROM_DRIVE_STATUS` 912 Returns the status of the drive by a call to 913 *drive_status()*. Return values are defined in cdrom_drive_status_. 914 Note that this call doesn't return information on the 915 current playing activity of the drive; this can be polled through 916 an *ioctl* call to *CDROMSUBCHNL*. For juke-boxes, an extra argument 917 *arg* specifies the slot for which (possibly limited) information is 918 given. The special value *CDSL_CURRENT* requests that information 919 about the currently selected slot be returned. 920`CDROM_DISC_STATUS` 921 Returns the type of the disc currently in the drive. 922 It should be viewed as a complement to *CDROM_DRIVE_STATUS*. 923 This *ioctl* can provide *some* information about the current 924 disc that is inserted in the drive. This functionality used to be 925 implemented in the low level drivers, but is now carried out 926 entirely in Uniform CD-ROM Driver. 927 928 The history of development of the CD's use as a carrier medium for 929 various digital information has lead to many different disc types. 930 This *ioctl* is useful only in the case that CDs have \emph {only 931 one} type of data on them. While this is often the case, it is 932 also very common for CDs to have some tracks with data, and some 933 tracks with audio. Because this is an existing interface, rather 934 than fixing this interface by changing the assumptions it was made 935 under, thereby breaking all user applications that use this 936 function, the Uniform CD-ROM Driver implements this *ioctl* as 937 follows: If the CD in question has audio tracks on it, and it has 938 absolutely no CD-I, XA, or data tracks on it, it will be reported 939 as *CDS_AUDIO*. If it has both audio and data tracks, it will 940 return *CDS_MIXED*. If there are no audio tracks on the disc, and 941 if the CD in question has any CD-I tracks on it, it will be 942 reported as *CDS_XA_2_2*. Failing that, if the CD in question 943 has any XA tracks on it, it will be reported as *CDS_XA_2_1*. 944 Finally, if the CD in question has any data tracks on it, 945 it will be reported as a data CD (*CDS_DATA_1*). 946 947 This *ioctl* can return:: 948 949 CDS_NO_INFO /* no information available */ 950 CDS_NO_DISC /* no disc is inserted, or tray is opened */ 951 CDS_AUDIO /* Audio disc (2352 audio bytes/frame) */ 952 CDS_DATA_1 /* data disc, mode 1 (2048 user bytes/frame) */ 953 CDS_XA_2_1 /* mixed data (XA), mode 2, form 1 (2048 user bytes) */ 954 CDS_XA_2_2 /* mixed data (XA), mode 2, form 1 (2324 user bytes) */ 955 CDS_MIXED /* mixed audio/data disc */ 956 957 For some information concerning frame layout of the various disc 958 types, see a recent version of `cdrom.h`. 959 960`CDROM_CHANGER_NSLOTS` 961 Returns the number of slots in a juke-box. 962`CDROMRESET` 963 Reset the drive. 964`CDROM_GET_CAPABILITY` 965 Returns the *capability* flags for the drive. Refer to section 966 cdrom_capabilities_ for more information on these flags. 967`CDROM_LOCKDOOR` 968 Locks the door of the drive. `arg == 0` unlocks the door, 969 any other value locks it. 970`CDROM_DEBUG` 971 Turns on debugging info. Only root is allowed to do this. 972 Same semantics as CDROM_LOCKDOOR. 973 974 975Device dependent *ioctl()'s* 976---------------------------- 977 978Finally, all other *ioctl()'s* are passed to the function *dev_ioctl()*, 979if implemented. No memory allocation or verification is carried out. 980 981How to update your driver 982========================= 983 984- Make a backup of your current driver. 985- Get hold of the files `cdrom.c` and `cdrom.h`, they should be in 986 the directory tree that came with this documentation. 987- Make sure you include `cdrom.h`. 988- Change the 3rd argument of *register_blkdev* from `&<your-drive>_fops` 989 to `&cdrom_fops`. 990- Just after that line, add the following to register with the Uniform 991 CD-ROM Driver:: 992 993 register_cdrom(&<your-drive>_info);* 994 995 Similarly, add a call to *unregister_cdrom()* at the appropriate place. 996- Copy an example of the device-operations *struct* to your 997 source, e. g., from `cm206.c` *cm206_dops*, and change all 998 entries to names corresponding to your driver, or names you just 999 happen to like. If your driver doesn't support a certain function, 1000 make the entry *NULL*. At the entry *capability* you should list all 1001 capabilities your driver currently supports. If your driver 1002 has a capability that is not listed, please send me a message. 1003- Copy the *cdrom_device_info* declaration from the same example 1004 driver, and modify the entries according to your needs. If your 1005 driver dynamically determines the capabilities of the hardware, this 1006 structure should also be declared dynamically. 1007- Implement all functions in your `<device>_dops` structure, 1008 according to prototypes listed in `cdrom.h`, and specifications given 1009 in cdrom_api_. Most likely you have already implemented 1010 the code in a large part, and you will almost certainly need to adapt the 1011 prototype and return values. 1012- Rename your `<device>_ioctl()` function to *audio_ioctl* and 1013 change the prototype a little. Remove entries listed in the first 1014 part in cdrom_ioctl_, if your code was OK, these are 1015 just calls to the routines you adapted in the previous step. 1016- You may remove all remaining memory checking code in the 1017 *audio_ioctl()* function that deals with audio commands (these are 1018 listed in the second part of cdrom_ioctl_. There is no 1019 need for memory allocation either, so most *case*s in the *switch* 1020 statement look similar to:: 1021 1022 case CDROMREADTOCENTRY: 1023 get_toc_entry\bigl((struct cdrom_tocentry *) arg); 1024 1025- All remaining *ioctl* cases must be moved to a separate 1026 function, *<device>_ioctl*, the device-dependent *ioctl()'s*. Note that 1027 memory checking and allocation must be kept in this code! 1028- Change the prototypes of *<device>_open()* and 1029 *<device>_release()*, and remove any strategic code (i. e., tray 1030 movement, door locking, etc.). 1031- Try to recompile the drivers. We advise you to use modules, both 1032 for `cdrom.o` and your driver, as debugging is much easier this 1033 way. 1034 1035Thanks 1036====== 1037 1038Thanks to all the people involved. First, Erik Andersen, who has 1039taken over the torch in maintaining `cdrom.c` and integrating much 1040CD-ROM-related code in the 2.1-kernel. Thanks to Scott Snyder and 1041Gerd Knorr, who were the first to implement this interface for SCSI 1042and IDE-CD drivers and added many ideas for extension of the data 1043structures relative to kernel~2.0. Further thanks to Heiko Eißfeldt, 1044Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard Mönkeberg and Andrew Kroll, 1045the Linux CD-ROM device driver developers who were kind 1046enough to give suggestions and criticisms during the writing. Finally 1047of course, I want to thank Linus Torvalds for making this possible in 1048the first place. 1049