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 (*select_disc)(struct cdrom_device_info *, int); 222 int (*get_last_session) (struct cdrom_device_info *, 223 struct cdrom_multisession *); 224 int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *); 225 int (*reset)(struct cdrom_device_info *); 226 int (*audio_ioctl)(struct cdrom_device_info *, 227 unsigned int, void *); 228 const int capability; /* capability flags */ 229 int (*generic_packet)(struct cdrom_device_info *, 230 struct packet_command *); 231 }; 232 233When a low-level device driver implements one of these capabilities, 234it should add a function pointer to this *struct*. When a particular 235function is not implemented, however, this *struct* should contain a 236NULL instead. The *capability* flags specify the capabilities of the 237CD-ROM hardware and/or low-level CD-ROM driver when a CD-ROM drive 238is registered with the Uniform CD-ROM Driver. 239 240Note that most functions have fewer parameters than their 241*blkdev_fops* counterparts. This is because very little of the 242information in the structures *inode* and *file* is used. For most 243drivers, the main parameter is the *struct* *cdrom_device_info*, from 244which the major and minor number can be extracted. (Most low-level 245CD-ROM drivers don't even look at the major and minor number though, 246since many of them only support one device.) This will be available 247through *dev* in *cdrom_device_info* described below. 248 249The drive-specific, minor-like information that is registered with 250`cdrom.c`, currently contains the following fields:: 251 252 struct cdrom_device_info { 253 const struct cdrom_device_ops * ops; /* device operations for this major */ 254 struct list_head list; /* linked list of all device_info */ 255 struct gendisk * disk; /* matching block layer disk */ 256 void * handle; /* driver-dependent data */ 257 258 int mask; /* mask of capability: disables them */ 259 int speed; /* maximum speed for reading data */ 260 int capacity; /* number of discs in a jukebox */ 261 262 unsigned int options:30; /* options flags */ 263 unsigned mc_flags:2; /* media-change buffer flags */ 264 unsigned int vfs_events; /* cached events for vfs path */ 265 unsigned int ioctl_events; /* cached events for ioctl path */ 266 int use_count; /* number of times device is opened */ 267 char name[20]; /* name of the device type */ 268 269 __u8 sanyo_slot : 2; /* Sanyo 3-CD changer support */ 270 __u8 keeplocked : 1; /* CDROM_LOCKDOOR status */ 271 __u8 reserved : 5; /* not used yet */ 272 int cdda_method; /* see CDDA_* flags */ 273 __u8 last_sense; /* saves last sense key */ 274 __u8 media_written; /* dirty flag, DVD+RW bookkeeping */ 275 unsigned short mmc3_profile; /* current MMC3 profile */ 276 int for_data; /* unknown:TBD */ 277 int (*exit)(struct cdrom_device_info *);/* unknown:TBD */ 278 int mrw_mode_page; /* which MRW mode page is in use */ 279 }; 280 281Using this *struct*, a linked list of the registered minor devices is 282built, using the *next* field. The device number, the device operations 283struct and specifications of properties of the drive are stored in this 284structure. 285 286The *mask* flags can be used to mask out some of the capabilities listed 287in *ops->capability*, if a specific drive doesn't support a feature 288of the driver. The value *speed* specifies the maximum head-rate of the 289drive, measured in units of normal audio speed (176kB/sec raw data or 290150kB/sec file system data). The parameters are declared *const* 291because they describe properties of the drive, which don't change after 292registration. 293 294A few registers contain variables local to the CD-ROM drive. The 295flags *options* are used to specify how the general CD-ROM routines 296should behave. These various flags registers should provide enough 297flexibility to adapt to the different users' wishes (and **not** the 298`arbitrary` wishes of the author of the low-level device driver, as is 299the case in the old scheme). The register *mc_flags* is used to buffer 300the information from *media_changed()* to two separate queues. Other 301data that is specific to a minor drive, can be accessed through *handle*, 302which can point to a data structure specific to the low-level driver. 303The fields *use_count*, *next*, *options* and *mc_flags* need not be 304initialized. 305 306The intermediate software layer that `cdrom.c` forms will perform some 307additional bookkeeping. The use count of the device (the number of 308processes that have the device opened) is registered in *use_count*. The 309function *cdrom_ioctl()* will verify the appropriate user-memory regions 310for read and write, and in case a location on the CD is transferred, 311it will `sanitize` the format by making requests to the low-level 312drivers in a standard format, and translating all formats between the 313user-software and low level drivers. This relieves much of the drivers' 314memory checking and format checking and translation. Also, the necessary 315structures will be declared on the program stack. 316 317The implementation of the functions should be as defined in the 318following sections. Two functions **must** be implemented, namely 319*open()* and *release()*. Other functions may be omitted, their 320corresponding capability flags will be cleared upon registration. 321Generally, a function returns zero on success and negative on error. A 322function call should return only after the command has completed, but of 323course waiting for the device should not use processor time. 324 325:: 326 327 int open(struct cdrom_device_info *cdi, int purpose) 328 329*Open()* should try to open the device for a specific *purpose*, which 330can be either: 331 332- Open for reading data, as done by `mount()` (2), or the 333 user commands `dd` or `cat`. 334- Open for *ioctl* commands, as done by audio-CD playing programs. 335 336Notice that any strategic code (closing tray upon *open()*, etc.) is 337done by the calling routine in `cdrom.c`, so the low-level routine 338should only be concerned with proper initialization, such as spinning 339up the disc, etc. 340 341:: 342 343 void release(struct cdrom_device_info *cdi) 344 345Device-specific actions should be taken such as spinning down the device. 346However, strategic actions such as ejection of the tray, or unlocking 347the door, should be left over to the general routine *cdrom_release()*. 348This is the only function returning type *void*. 349 350.. _cdrom_drive_status: 351 352:: 353 354 int drive_status(struct cdrom_device_info *cdi, int slot_nr) 355 356The function *drive_status*, if implemented, should provide 357information on the status of the drive (not the status of the disc, 358which may or may not be in the drive). If the drive is not a changer, 359*slot_nr* should be ignored. In `cdrom.h` the possibilities are listed:: 360 361 362 CDS_NO_INFO /* no information available */ 363 CDS_NO_DISC /* no disc is inserted, tray is closed */ 364 CDS_TRAY_OPEN /* tray is opened */ 365 CDS_DRIVE_NOT_READY /* something is wrong, tray is moving? */ 366 CDS_DISC_OK /* a disc is loaded and everything is fine */ 367 368:: 369 370 int tray_move(struct cdrom_device_info *cdi, int position) 371 372This function, if implemented, should control the tray movement. (No 373other function should control this.) The parameter *position* controls 374the desired direction of movement: 375 376- 0 Close tray 377- 1 Open tray 378 379This function returns 0 upon success, and a non-zero value upon 380error. Note that if the tray is already in the desired position, no 381action need be taken, and the return value should be 0. 382 383:: 384 385 int lock_door(struct cdrom_device_info *cdi, int lock) 386 387This function (and no other code) controls locking of the door, if the 388drive allows this. The value of *lock* controls the desired locking 389state: 390 391- 0 Unlock door, manual opening is allowed 392- 1 Lock door, tray cannot be ejected manually 393 394This function returns 0 upon success, and a non-zero value upon 395error. Note that if the door is already in the requested state, no 396action need be taken, and the return value should be 0. 397 398:: 399 400 int select_speed(struct cdrom_device_info *cdi, int speed) 401 402Some CD-ROM drives are capable of changing their head-speed. There 403are several reasons for changing the speed of a CD-ROM drive. Badly 404pressed CD-ROM s may benefit from less-than-maximum head rate. Modern 405CD-ROM drives can obtain very high head rates (up to *24x* is 406common). It has been reported that these drives can make reading 407errors at these high speeds, reducing the speed can prevent data loss 408in these circumstances. Finally, some of these drives can 409make an annoyingly loud noise, which a lower speed may reduce. 410 411This function specifies the speed at which data is read or audio is 412played back. The value of *speed* specifies the head-speed of the 413drive, measured in units of standard cdrom speed (176kB/sec raw data 414or 150kB/sec file system data). So to request that a CD-ROM drive 415operate at 300kB/sec you would call the CDROM_SELECT_SPEED *ioctl* 416with *speed=2*. The special value `0` means `auto-selection`, i. e., 417maximum data-rate or real-time audio rate. If the drive doesn't have 418this `auto-selection` capability, the decision should be made on the 419current disc loaded and the return value should be positive. A negative 420return value indicates an error. 421 422:: 423 424 int select_disc(struct cdrom_device_info *cdi, int number) 425 426If the drive can store multiple discs (a juke-box) this function 427will perform disc selection. It should return the number of the 428selected disc on success, a negative value on error. Currently, only 429the ide-cd driver supports this functionality. 430 431:: 432 433 int get_last_session(struct cdrom_device_info *cdi, 434 struct cdrom_multisession *ms_info) 435 436This function should implement the old corresponding *ioctl()*. For 437device *cdi->dev*, the start of the last session of the current disc 438should be returned in the pointer argument *ms_info*. Note that 439routines in `cdrom.c` have sanitized this argument: its requested 440format will **always** be of the type *CDROM_LBA* (linear block 441addressing mode), whatever the calling software requested. But 442sanitization goes even further: the low-level implementation may 443return the requested information in *CDROM_MSF* format if it wishes so 444(setting the *ms_info->addr_format* field appropriately, of 445course) and the routines in `cdrom.c` will make the transformation if 446necessary. The return value is 0 upon success. 447 448:: 449 450 int get_mcn(struct cdrom_device_info *cdi, 451 struct cdrom_mcn *mcn) 452 453Some discs carry a `Media Catalog Number` (MCN), also called 454`Universal Product Code` (UPC). This number should reflect the number 455that is generally found in the bar-code on the product. Unfortunately, 456the few discs that carry such a number on the disc don't even use the 457same format. The return argument to this function is a pointer to a 458pre-declared memory region of type *struct cdrom_mcn*. The MCN is 459expected as a 13-character string, terminated by a null-character. 460 461:: 462 463 int reset(struct cdrom_device_info *cdi) 464 465This call should perform a hard-reset on the drive (although in 466circumstances that a hard-reset is necessary, a drive may very well not 467listen to commands anymore). Preferably, control is returned to the 468caller only after the drive has finished resetting. If the drive is no 469longer listening, it may be wise for the underlying low-level cdrom 470driver to time out. 471 472:: 473 474 int audio_ioctl(struct cdrom_device_info *cdi, 475 unsigned int cmd, void *arg) 476 477Some of the CD-ROM-\ *ioctl()*\ 's defined in `cdrom.h` can be 478implemented by the routines described above, and hence the function 479*cdrom_ioctl* will use those. However, most *ioctl()*\ 's deal with 480audio-control. We have decided to leave these to be accessed through a 481single function, repeating the arguments *cmd* and *arg*. Note that 482the latter is of type *void*, rather than *unsigned long int*. 483The routine *cdrom_ioctl()* does do some useful things, 484though. It sanitizes the address format type to *CDROM_MSF* (Minutes, 485Seconds, Frames) for all audio calls. It also verifies the memory 486location of *arg*, and reserves stack-memory for the argument. This 487makes implementation of the *audio_ioctl()* much simpler than in the 488old driver scheme. For example, you may look up the function 489*cm206_audio_ioctl()* `cm206.c` that should be updated with 490this documentation. 491 492An unimplemented ioctl should return *-ENOSYS*, but a harmless request 493(e. g., *CDROMSTART*) may be ignored by returning 0 (success). Other 494errors should be according to the standards, whatever they are. When 495an error is returned by the low-level driver, the Uniform CD-ROM Driver 496tries whenever possible to return the error code to the calling program. 497(We may decide to sanitize the return value in *cdrom_ioctl()* though, in 498order to guarantee a uniform interface to the audio-player software.) 499 500:: 501 502 int dev_ioctl(struct cdrom_device_info *cdi, 503 unsigned int cmd, unsigned long arg) 504 505Some *ioctl()'s* seem to be specific to certain CD-ROM drives. That is, 506they are introduced to service some capabilities of certain drives. In 507fact, there are 6 different *ioctl()'s* for reading data, either in some 508particular kind of format, or audio data. Not many drives support 509reading audio tracks as data, I believe this is because of protection 510of copyrights of artists. Moreover, I think that if audio-tracks are 511supported, it should be done through the VFS and not via *ioctl()'s*. A 512problem here could be the fact that audio-frames are 2352 bytes long, 513so either the audio-file-system should ask for 75264 bytes at once 514(the least common multiple of 512 and 2352), or the drivers should 515bend their backs to cope with this incoherence (to which I would be 516opposed). Furthermore, it is very difficult for the hardware to find 517the exact frame boundaries, since there are no synchronization headers 518in audio frames. Once these issues are resolved, this code should be 519standardized in `cdrom.c`. 520 521Because there are so many *ioctl()'s* that seem to be introduced to 522satisfy certain drivers [#f2]_, any non-standard *ioctl()*\ s 523are routed through the call *dev_ioctl()*. In principle, `private` 524*ioctl()*\ 's should be numbered after the device's major number, and not 525the general CD-ROM *ioctl* number, `0x53`. Currently the 526non-supported *ioctl()'s* are: 527 528 CDROMREADMODE1, CDROMREADMODE2, CDROMREADAUDIO, CDROMREADRAW, 529 CDROMREADCOOKED, CDROMSEEK, CDROMPLAY-BLK and CDROM-READALL 530 531.. [#f2] 532 533 Is there software around that actually uses these? I'd be interested! 534 535.. _cdrom_capabilities: 536 537CD-ROM capabilities 538------------------- 539 540Instead of just implementing some *ioctl* calls, the interface in 541`cdrom.c` supplies the possibility to indicate the **capabilities** 542of a CD-ROM drive. This can be done by ORing any number of 543capability-constants that are defined in `cdrom.h` at the registration 544phase. Currently, the capabilities are any of:: 545 546 CDC_CLOSE_TRAY /* can close tray by software control */ 547 CDC_OPEN_TRAY /* can open tray */ 548 CDC_LOCK /* can lock and unlock the door */ 549 CDC_SELECT_SPEED /* can select speed, in units of * sim*150 ,kB/s */ 550 CDC_SELECT_DISC /* drive is juke-box */ 551 CDC_MULTI_SESSION /* can read sessions *> rm1* */ 552 CDC_MCN /* can read Media Catalog Number */ 553 CDC_MEDIA_CHANGED /* can report if disc has changed */ 554 CDC_PLAY_AUDIO /* can perform audio-functions (play, pause, etc) */ 555 CDC_RESET /* hard reset device */ 556 CDC_IOCTLS /* driver has non-standard ioctls */ 557 CDC_DRIVE_STATUS /* driver implements drive status */ 558 559The capability flag is declared *const*, to prevent drivers from 560accidentally tampering with the contents. The capability flags actually 561inform `cdrom.c` of what the driver can do. If the drive found 562by the driver does not have the capability, is can be masked out by 563the *cdrom_device_info* variable *mask*. For instance, the SCSI CD-ROM 564driver has implemented the code for loading and ejecting CD-ROM's, and 565hence its corresponding flags in *capability* will be set. But a SCSI 566CD-ROM drive might be a caddy system, which can't load the tray, and 567hence for this drive the *cdrom_device_info* struct will have set 568the *CDC_CLOSE_TRAY* bit in *mask*. 569 570In the file `cdrom.c` you will encounter many constructions of the type:: 571 572 if (cdo->capability & ∼cdi->mask & CDC _⟨capability⟩) ... 573 574There is no *ioctl* to set the mask... The reason is that 575I think it is better to control the **behavior** rather than the 576**capabilities**. 577 578Options 579------- 580 581A final flag register controls the **behavior** of the CD-ROM 582drives, in order to satisfy different users' wishes, hopefully 583independently of the ideas of the respective author who happened to 584have made the drive's support available to the Linux community. The 585current behavior options are:: 586 587 CDO_AUTO_CLOSE /* try to close tray upon device open() */ 588 CDO_AUTO_EJECT /* try to open tray on last device close() */ 589 CDO_USE_FFLAGS /* use file_pointer->f_flags to indicate purpose for open() */ 590 CDO_LOCK /* try to lock door if device is opened */ 591 CDO_CHECK_TYPE /* ensure disc type is data if opened for data */ 592 593The initial value of this register is 594`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK`, reflecting my own view on user 595interface and software standards. Before you protest, there are two 596new *ioctl()'s* implemented in `cdrom.c`, that allow you to control the 597behavior by software. These are:: 598 599 CDROM_SET_OPTIONS /* set options specified in (int)arg */ 600 CDROM_CLEAR_OPTIONS /* clear options specified in (int)arg */ 601 602One option needs some more explanation: *CDO_USE_FFLAGS*. In the next 603newsection we explain what the need for this option is. 604 605A software package `setcd`, available from the Debian distribution 606and `sunsite.unc.edu`, allows user level control of these flags. 607 608 609The need to know the purpose of opening the CD-ROM device 610========================================================= 611 612Traditionally, Unix devices can be used in two different `modes`, 613either by reading/writing to the device file, or by issuing 614controlling commands to the device, by the device's *ioctl()* 615call. The problem with CD-ROM drives, is that they can be used for 616two entirely different purposes. One is to mount removable 617file systems, CD-ROM's, the other is to play audio CD's. Audio commands 618are implemented entirely through *ioctl()\'s*, presumably because the 619first implementation (SUN?) has been such. In principle there is 620nothing wrong with this, but a good control of the `CD player` demands 621that the device can **always** be opened in order to give the 622*ioctl* commands, regardless of the state the drive is in. 623 624On the other hand, when used as a removable-media disc drive (what the 625original purpose of CD-ROM s is) we would like to make sure that the 626disc drive is ready for operation upon opening the device. In the old 627scheme, some CD-ROM drivers don't do any integrity checking, resulting 628in a number of i/o errors reported by the VFS to the kernel when an 629attempt for mounting a CD-ROM on an empty drive occurs. This is not a 630particularly elegant way to find out that there is no CD-ROM inserted; 631it more-or-less looks like the old IBM-PC trying to read an empty floppy 632drive for a couple of seconds, after which the system complains it 633can't read from it. Nowadays we can **sense** the existence of a 634removable medium in a drive, and we believe we should exploit that 635fact. An integrity check on opening of the device, that verifies the 636availability of a CD-ROM and its correct type (data), would be 637desirable. 638 639These two ways of using a CD-ROM drive, principally for data and 640secondarily for playing audio discs, have different demands for the 641behavior of the *open()* call. Audio use simply wants to open the 642device in order to get a file handle which is needed for issuing 643*ioctl* commands, while data use wants to open for correct and 644reliable data transfer. The only way user programs can indicate what 645their *purpose* of opening the device is, is through the *flags* 646parameter (see `open(2)`). For CD-ROM devices, these flags aren't 647implemented (some drivers implement checking for write-related flags, 648but this is not strictly necessary if the device file has correct 649permission flags). Most option flags simply don't make sense to 650CD-ROM devices: *O_CREAT*, *O_NOCTTY*, *O_TRUNC*, *O_APPEND*, and 651*O_SYNC* have no meaning to a CD-ROM. 652 653We therefore propose to use the flag *O_NONBLOCK* to indicate 654that the device is opened just for issuing *ioctl* 655commands. Strictly, the meaning of *O_NONBLOCK* is that opening and 656subsequent calls to the device don't cause the calling process to 657wait. We could interpret this as don't wait until someone has 658inserted some valid data-CD-ROM. Thus, our proposal of the 659implementation for the *open()* call for CD-ROM s is: 660 661- If no other flags are set than *O_RDONLY*, the device is opened 662 for data transfer, and the return value will be 0 only upon successful 663 initialization of the transfer. The call may even induce some actions 664 on the CD-ROM, such as closing the tray. 665- If the option flag *O_NONBLOCK* is set, opening will always be 666 successful, unless the whole device doesn't exist. The drive will take 667 no actions whatsoever. 668 669And what about standards? 670------------------------- 671 672You might hesitate to accept this proposal as it comes from the 673Linux community, and not from some standardizing institute. What 674about SUN, SGI, HP and all those other Unix and hardware vendors? 675Well, these companies are in the lucky position that they generally 676control both the hardware and software of their supported products, 677and are large enough to set their own standard. They do not have to 678deal with a dozen or more different, competing hardware 679configurations\ [#f3]_. 680 681.. [#f3] 682 683 Incidentally, I think that SUN's approach to mounting CD-ROM s is very 684 good in origin: under Solaris a volume-daemon automatically mounts a 685 newly inserted CD-ROM under `/cdrom/*<volume-name>*`. 686 687 In my opinion they should have pushed this 688 further and have **every** CD-ROM on the local area network be 689 mounted at the similar location, i. e., no matter in which particular 690 machine you insert a CD-ROM, it will always appear at the same 691 position in the directory tree, on every system. When I wanted to 692 implement such a user-program for Linux, I came across the 693 differences in behavior of the various drivers, and the need for an 694 *ioctl* informing about media changes. 695 696We believe that using *O_NONBLOCK* to indicate that a device is being opened 697for *ioctl* commands only can be easily introduced in the Linux 698community. All the CD-player authors will have to be informed, we can 699even send in our own patches to the programs. The use of *O_NONBLOCK* 700has most likely no influence on the behavior of the CD-players on 701other operating systems than Linux. Finally, a user can always revert 702to old behavior by a call to 703*ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, CDO_USE_FFLAGS)*. 704 705The preferred strategy of *open()* 706---------------------------------- 707 708The routines in `cdrom.c` are designed in such a way that run-time 709configuration of the behavior of CD-ROM devices (of **any** type) 710can be carried out, by the *CDROM_SET/CLEAR_OPTIONS* *ioctls*. Thus, various 711modes of operation can be set: 712 713`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK` 714 This is the default setting. (With *CDO_CHECK_TYPE* it will be better, in 715 the future.) If the device is not yet opened by any other process, and if 716 the device is being opened for data (*O_NONBLOCK* is not set) and the 717 tray is found to be open, an attempt to close the tray is made. Then, 718 it is verified that a disc is in the drive and, if *CDO_CHECK_TYPE* is 719 set, that it contains tracks of type `data mode 1`. Only if all tests 720 are passed is the return value zero. The door is locked to prevent file 721 system corruption. If the drive is opened for audio (*O_NONBLOCK* is 722 set), no actions are taken and a value of 0 will be returned. 723 724`CDO_AUTO_CLOSE | CDO_AUTO_EJECT | CDO_LOCK` 725 This mimics the behavior of the current sbpcd-driver. The option flags are 726 ignored, the tray is closed on the first open, if necessary. Similarly, 727 the tray is opened on the last release, i. e., if a CD-ROM is unmounted, 728 it is automatically ejected, such that the user can replace it. 729 730We hope that these option can convince everybody (both driver 731maintainers and user program developers) to adopt the new CD-ROM 732driver scheme and option flag interpretation. 733 734Description of routines in `cdrom.c` 735==================================== 736 737Only a few routines in `cdrom.c` are exported to the drivers. In this 738new section we will discuss these, as well as the functions that `take 739over` the CD-ROM interface to the kernel. The header file belonging 740to `cdrom.c` is called `cdrom.h`. Formerly, some of the contents of this 741file were placed in the file `ucdrom.h`, but this file has now been 742merged back into `cdrom.h`. 743 744:: 745 746 struct file_operations cdrom_fops 747 748The contents of this structure were described in cdrom_api_. 749A pointer to this structure is assigned to the *fops* field 750of the *struct gendisk*. 751 752:: 753 754 int register_cdrom(struct cdrom_device_info *cdi) 755 756This function is used in about the same way one registers *cdrom_fops* 757with the kernel, the device operations and information structures, 758as described in cdrom_api_, should be registered with the 759Uniform CD-ROM Driver:: 760 761 register_cdrom(&<device>_info); 762 763 764This function returns zero upon success, and non-zero upon 765failure. The structure *<device>_info* should have a pointer to the 766driver's *<device>_dops*, as in:: 767 768 struct cdrom_device_info <device>_info = { 769 <device>_dops; 770 ... 771 } 772 773Note that a driver must have one static structure, *<device>_dops*, while 774it may have as many structures *<device>_info* as there are minor devices 775active. *Register_cdrom()* builds a linked list from these. 776 777 778:: 779 780 void unregister_cdrom(struct cdrom_device_info *cdi) 781 782Unregistering device *cdi* with minor number *MINOR(cdi->dev)* removes 783the minor device from the list. If it was the last registered minor for 784the low-level driver, this disconnects the registered device-operation 785routines from the CD-ROM interface. This function returns zero upon 786success, and non-zero upon failure. 787 788:: 789 790 int cdrom_open(struct inode * ip, struct file * fp) 791 792This function is not called directly by the low-level drivers, it is 793listed in the standard *cdrom_fops*. If the VFS opens a file, this 794function becomes active. A strategy is implemented in this routine, 795taking care of all capabilities and options that are set in the 796*cdrom_device_ops* connected to the device. Then, the program flow is 797transferred to the device_dependent *open()* call. 798 799:: 800 801 void cdrom_release(struct inode *ip, struct file *fp) 802 803This function implements the reverse-logic of *cdrom_open()*, and then 804calls the device-dependent *release()* routine. When the use-count has 805reached 0, the allocated buffers are flushed by calls to *sync_dev(dev)* 806and *invalidate_buffers(dev)*. 807 808 809.. _cdrom_ioctl: 810 811:: 812 813 int cdrom_ioctl(struct inode *ip, struct file *fp, 814 unsigned int cmd, unsigned long arg) 815 816This function handles all the standard *ioctl* requests for CD-ROM 817devices in a uniform way. The different calls fall into three 818categories: *ioctl()'s* that can be directly implemented by device 819operations, ones that are routed through the call *audio_ioctl()*, and 820the remaining ones, that are presumable device-dependent. Generally, a 821negative return value indicates an error. 822 823Directly implemented *ioctl()'s* 824-------------------------------- 825 826The following `old` CD-ROM *ioctl()*\ 's are implemented by directly 827calling device-operations in *cdrom_device_ops*, if implemented and 828not masked: 829 830`CDROMMULTISESSION` 831 Requests the last session on a CD-ROM. 832`CDROMEJECT` 833 Open tray. 834`CDROMCLOSETRAY` 835 Close tray. 836`CDROMEJECT_SW` 837 If *arg\not=0*, set behavior to auto-close (close 838 tray on first open) and auto-eject (eject on last release), otherwise 839 set behavior to non-moving on *open()* and *release()* calls. 840`CDROM_GET_MCN` 841 Get the Media Catalog Number from a CD. 842 843*Ioctl*s routed through *audio_ioctl()* 844--------------------------------------- 845 846The following set of *ioctl()'s* are all implemented through a call to 847the *cdrom_fops* function *audio_ioctl()*. Memory checks and 848allocation are performed in *cdrom_ioctl()*, and also sanitization of 849address format (*CDROM_LBA*/*CDROM_MSF*) is done. 850 851`CDROMSUBCHNL` 852 Get sub-channel data in argument *arg* of type 853 `struct cdrom_subchnl *`. 854`CDROMREADTOCHDR` 855 Read Table of Contents header, in *arg* of type 856 `struct cdrom_tochdr *`. 857`CDROMREADTOCENTRY` 858 Read a Table of Contents entry in *arg* and specified by *arg* 859 of type `struct cdrom_tocentry *`. 860`CDROMPLAYMSF` 861 Play audio fragment specified in Minute, Second, Frame format, 862 delimited by *arg* of type `struct cdrom_msf *`. 863`CDROMPLAYTRKIND` 864 Play audio fragment in track-index format delimited by *arg* 865 of type `struct cdrom_ti *`. 866`CDROMVOLCTRL` 867 Set volume specified by *arg* of type `struct cdrom_volctrl *`. 868`CDROMVOLREAD` 869 Read volume into by *arg* of type `struct cdrom_volctrl *`. 870`CDROMSTART` 871 Spin up disc. 872`CDROMSTOP` 873 Stop playback of audio fragment. 874`CDROMPAUSE` 875 Pause playback of audio fragment. 876`CDROMRESUME` 877 Resume playing. 878 879New *ioctl()'s* in `cdrom.c` 880---------------------------- 881 882The following *ioctl()'s* have been introduced to allow user programs to 883control the behavior of individual CD-ROM devices. New *ioctl* 884commands can be identified by the underscores in their names. 885 886`CDROM_SET_OPTIONS` 887 Set options specified by *arg*. Returns the option flag register 888 after modification. Use *arg = \rm0* for reading the current flags. 889`CDROM_CLEAR_OPTIONS` 890 Clear options specified by *arg*. Returns the option flag register 891 after modification. 892`CDROM_SELECT_SPEED` 893 Select head-rate speed of disc specified as by *arg* in units 894 of standard cdrom speed (176\,kB/sec raw data or 895 150kB/sec file system data). The value 0 means `auto-select`, 896 i. e., play audio discs at real time and data discs at maximum speed. 897 The value *arg* is checked against the maximum head rate of the 898 drive found in the *cdrom_dops*. 899`CDROM_SELECT_DISC` 900 Select disc numbered *arg* from a juke-box. 901 902 First disc is numbered 0. The number *arg* is checked against the 903 maximum number of discs in the juke-box found in the *cdrom_dops*. 904`CDROM_MEDIA_CHANGED` 905 Returns 1 if a disc has been changed since the last call. 906 For juke-boxes, an extra argument *arg* 907 specifies the slot for which the information is given. The special 908 value *CDSL_CURRENT* requests that information about the currently 909 selected slot be returned. 910`CDROM_DRIVE_STATUS` 911 Returns the status of the drive by a call to 912 *drive_status()*. Return values are defined in cdrom_drive_status_. 913 Note that this call doesn't return information on the 914 current playing activity of the drive; this can be polled through 915 an *ioctl* call to *CDROMSUBCHNL*. For juke-boxes, an extra argument 916 *arg* specifies the slot for which (possibly limited) information is 917 given. The special value *CDSL_CURRENT* requests that information 918 about the currently selected slot be returned. 919`CDROM_DISC_STATUS` 920 Returns the type of the disc currently in the drive. 921 It should be viewed as a complement to *CDROM_DRIVE_STATUS*. 922 This *ioctl* can provide *some* information about the current 923 disc that is inserted in the drive. This functionality used to be 924 implemented in the low level drivers, but is now carried out 925 entirely in Uniform CD-ROM Driver. 926 927 The history of development of the CD's use as a carrier medium for 928 various digital information has lead to many different disc types. 929 This *ioctl* is useful only in the case that CDs have \emph {only 930 one} type of data on them. While this is often the case, it is 931 also very common for CDs to have some tracks with data, and some 932 tracks with audio. Because this is an existing interface, rather 933 than fixing this interface by changing the assumptions it was made 934 under, thereby breaking all user applications that use this 935 function, the Uniform CD-ROM Driver implements this *ioctl* as 936 follows: If the CD in question has audio tracks on it, and it has 937 absolutely no CD-I, XA, or data tracks on it, it will be reported 938 as *CDS_AUDIO*. If it has both audio and data tracks, it will 939 return *CDS_MIXED*. If there are no audio tracks on the disc, and 940 if the CD in question has any CD-I tracks on it, it will be 941 reported as *CDS_XA_2_2*. Failing that, if the CD in question 942 has any XA tracks on it, it will be reported as *CDS_XA_2_1*. 943 Finally, if the CD in question has any data tracks on it, 944 it will be reported as a data CD (*CDS_DATA_1*). 945 946 This *ioctl* can return:: 947 948 CDS_NO_INFO /* no information available */ 949 CDS_NO_DISC /* no disc is inserted, or tray is opened */ 950 CDS_AUDIO /* Audio disc (2352 audio bytes/frame) */ 951 CDS_DATA_1 /* data disc, mode 1 (2048 user bytes/frame) */ 952 CDS_XA_2_1 /* mixed data (XA), mode 2, form 1 (2048 user bytes) */ 953 CDS_XA_2_2 /* mixed data (XA), mode 2, form 1 (2324 user bytes) */ 954 CDS_MIXED /* mixed audio/data disc */ 955 956 For some information concerning frame layout of the various disc 957 types, see a recent version of `cdrom.h`. 958 959`CDROM_CHANGER_NSLOTS` 960 Returns the number of slots in a juke-box. 961`CDROMRESET` 962 Reset the drive. 963`CDROM_GET_CAPABILITY` 964 Returns the *capability* flags for the drive. Refer to section 965 cdrom_capabilities_ for more information on these flags. 966`CDROM_LOCKDOOR` 967 Locks the door of the drive. `arg == 0` unlocks the door, 968 any other value locks it. 969`CDROM_DEBUG` 970 Turns on debugging info. Only root is allowed to do this. 971 Same semantics as CDROM_LOCKDOOR. 972 973 974Device dependent *ioctl()'s* 975---------------------------- 976 977Finally, all other *ioctl()'s* are passed to the function *dev_ioctl()*, 978if implemented. No memory allocation or verification is carried out. 979 980How to update your driver 981========================= 982 983- Make a backup of your current driver. 984- Get hold of the files `cdrom.c` and `cdrom.h`, they should be in 985 the directory tree that came with this documentation. 986- Make sure you include `cdrom.h`. 987- Change the 3rd argument of *register_blkdev* from `&<your-drive>_fops` 988 to `&cdrom_fops`. 989- Just after that line, add the following to register with the Uniform 990 CD-ROM Driver:: 991 992 register_cdrom(&<your-drive>_info);* 993 994 Similarly, add a call to *unregister_cdrom()* at the appropriate place. 995- Copy an example of the device-operations *struct* to your 996 source, e. g., from `cm206.c` *cm206_dops*, and change all 997 entries to names corresponding to your driver, or names you just 998 happen to like. If your driver doesn't support a certain function, 999 make the entry *NULL*. At the entry *capability* you should list all 1000 capabilities your driver currently supports. If your driver 1001 has a capability that is not listed, please send me a message. 1002- Copy the *cdrom_device_info* declaration from the same example 1003 driver, and modify the entries according to your needs. If your 1004 driver dynamically determines the capabilities of the hardware, this 1005 structure should also be declared dynamically. 1006- Implement all functions in your `<device>_dops` structure, 1007 according to prototypes listed in `cdrom.h`, and specifications given 1008 in cdrom_api_. Most likely you have already implemented 1009 the code in a large part, and you will almost certainly need to adapt the 1010 prototype and return values. 1011- Rename your `<device>_ioctl()` function to *audio_ioctl* and 1012 change the prototype a little. Remove entries listed in the first 1013 part in cdrom_ioctl_, if your code was OK, these are 1014 just calls to the routines you adapted in the previous step. 1015- You may remove all remaining memory checking code in the 1016 *audio_ioctl()* function that deals with audio commands (these are 1017 listed in the second part of cdrom_ioctl_. There is no 1018 need for memory allocation either, so most *case*s in the *switch* 1019 statement look similar to:: 1020 1021 case CDROMREADTOCENTRY: 1022 get_toc_entry\bigl((struct cdrom_tocentry *) arg); 1023 1024- All remaining *ioctl* cases must be moved to a separate 1025 function, *<device>_ioctl*, the device-dependent *ioctl()'s*. Note that 1026 memory checking and allocation must be kept in this code! 1027- Change the prototypes of *<device>_open()* and 1028 *<device>_release()*, and remove any strategic code (i. e., tray 1029 movement, door locking, etc.). 1030- Try to recompile the drivers. We advise you to use modules, both 1031 for `cdrom.o` and your driver, as debugging is much easier this 1032 way. 1033 1034Thanks 1035====== 1036 1037Thanks to all the people involved. First, Erik Andersen, who has 1038taken over the torch in maintaining `cdrom.c` and integrating much 1039CD-ROM-related code in the 2.1-kernel. Thanks to Scott Snyder and 1040Gerd Knorr, who were the first to implement this interface for SCSI 1041and IDE-CD drivers and added many ideas for extension of the data 1042structures relative to kernel~2.0. Further thanks to Heiko Eißfeldt, 1043Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard Mönkeberg and Andrew Kroll, 1044the Linux CD-ROM device driver developers who were kind 1045enough to give suggestions and criticisms during the writing. Finally 1046of course, I want to thank Linus Torvalds for making this possible in 1047the first place. 1048