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  \def\version{$Id: cdrom-standard.tex,v 1.9 1997/12/28 15:42:49 david Exp $}
  
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  \def\linux{{\sc Linux}}
  \def\cdrom{{\sc cd-rom}}
  \def\UCD{{\sc Uniform cd-rom Driver}}
  \def\cdromc{{\tt {cdrom.c}}}
  \def\cdromh{{\tt {cdrom.h}}}
  \def\fo{\sl}                    % foreign words
  \def\ie{{\fo i.e.}}
  \def\eg{{\fo e.g.}}
  
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  \begin{document}
  \title{A \linux\ \cdrom\ standard}
  \author{David van Leeuwen\\{
  ormalsize\tt david@ElseWare.cistron.nl}
  \\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}}
  \\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}}
  \date{12 March 1999}
  
  \maketitle
  
  
  ewsection{Introduction}
  
  \linux\ is probably the Unix-like operating system that supports
  the widest variety of hardware devices. The reasons for this are
  presumably 
  \begin{itemize} 
  \item 
    The large list of hardware devices available for the many platforms
    that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.)
  \item 
    The open design of the operating system, such that anybody can write a
    driver for \linux.
  \item 
    There is plenty of source code around as examples of how to write a driver.
  \end{itemize}
  The openness of \linux, and the many different types of available
  hardware has allowed \linux\ to support many different hardware devices.
  Unfortunately, the very openness that has allowed \linux\ to support
  all these different devices has also allowed the behavior of each
  device driver to differ significantly from one device to another.
  This divergence of behavior has been very significant for \cdrom\
  devices; the way a particular drive reacts to a `standard' $ioctl()$
  call varies greatly from one device driver to another. To avoid making
  their drivers totally inconsistent, the writers of \linux\ \cdrom\
  drivers generally created new device drivers by understanding, copying,
  and then changing an existing one. Unfortunately, this practice did not
  maintain uniform behavior across all the \linux\ \cdrom\ drivers. 
  
  This document describes an effort to establish Uniform behavior across
  all the different \cdrom\ device drivers for \linux. This document also
  defines the various $ioctl$s, and how the low-level \cdrom\ device
  drivers should implement them. Currently (as of the \linux\ 2.1.$x$
  development kernels) several low-level \cdrom\ device drivers, including
  both IDE/ATAPI and SCSI, now use this Uniform interface.
  
  When the \cdrom\ was developed, the interface between the \cdrom\ drive
  and the computer was not specified in the standards. As a result, many
  different \cdrom\ interfaces were developed. Some of them had their
  own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
  manufacturers adopted an existing electrical interface and changed
  the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
  adapted their drives to one or more of the already existing electrical
  interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
  most of the `NoName' manufacturers). In cases where a new drive really
  brought its own interface or used its own command set and flow control
  scheme, either a separate driver had to be written, or an existing
  driver had to be enhanced. History has delivered us \cdrom\ support for
  many of these different interfaces. Nowadays, almost all new \cdrom\
  drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
  manufacturer will create a new interface. Even finding drives for the
  old proprietary interfaces is getting difficult.
  
  When (in the 1.3.70's) I looked at the existing software interface,
  which was expressed through \cdromh, it appeared to be a rather wild
  set of commands and data formats.\footnote{I cannot recollect what
  kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
  latest kernel that I was indirectly involved in.} It seemed that many
  features of the software interface had been added to accommodate the
  capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
  importantly, it appeared that the behavior of the `standard' commands
  was different for most of the different drivers: \eg, some drivers
  close the tray if an $open()$ call occurs when the tray is open, while
  others do not. Some drivers lock the door upon opening the device, to
  prevent an incoherent file system, but others don't, to allow software
  ejection. Undoubtedly, the capabilities of the different drives vary,
  but even when two drives have the same capability their drivers'
  behavior was usually different.
  
  I decided to start a discussion on how to make all the \linux\ \cdrom\
  drivers behave more uniformly. I began by contacting the developers of
  the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
  encouraged me to write the \UCD\ which this document is intended to
  describe. The implementation of the \UCD\ is in the file \cdromc. This
  driver is intended to be an additional software layer that sits on top
  of the low-level device drivers for each \cdrom\ drive. By adding this
  additional layer, it is possible to have all the different \cdrom\
  devices behave {\em exactly\/} the same (insofar as the underlying
  hardware will allow).
  
  The goal of the \UCD\ is {\em not\/} to alienate driver developers who
  have not yet taken steps to support this effort. The goal of \UCD\ is
  simply to give people writing application programs for \cdrom\ drives
  {\em one\/} \linux\ \cdrom\ interface with consistent behavior for all
  \cdrom\ devices. In addition, this also provides a consistent interface
  between the low-level device driver code and the \linux\ kernel. Care
  is taken that 100\,\% compatibility exists with the data structures and
  programmer's interface defined in \cdromh. This guide was written to
  help \cdrom\ driver developers adapt their code to use the \UCD\ code
  defined in \cdromc.
  
  Personally, I think that the most important hardware interfaces are
  the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
  of hardware drop continuously, it is also likely that people may have
  more than one \cdrom\ drive, possibly of mixed types. It is important
  that these drives behave in the same way. In December 1994, one of the
  cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
  drive. In the months that I was busy writing a \linux\ driver for it,
  proprietary drives became obsolete and IDE/ATAPI drives became the
  standard. At the time of the last update to this document (November
  1997) it is becoming difficult to even {\em find} anything less than a
  16 speed \cdrom\ drive, and 24 speed drives are common.
  
  
  ewsection{Standardizing through another software level}
  \label{cdrom.c}
  
  At the time this document was conceived, all drivers directly
  implemented the \cdrom\ $ioctl()$ calls through their own routines. This
  led to the danger of different drivers forgetting to do important things
  like checking that the user was giving the driver valid data. More
  importantly, this led to the divergence of behavior, which has already
  been discussed.
  
  For this reason, the \UCD\ was created to enforce consistent \cdrom\
  drive behavior, and to provide a common set of services to the various
  low-level \cdrom\ device drivers. The \UCD\ now provides another
  software-level, that separates the $ioctl()$ and $open()$ implementation
  from the actual hardware implementation. Note that this effort has
  made few changes which will affect a user's application programs. The
  greatest change involved moving the contents of the various low-level
  \cdrom\ drivers' header files to the kernel's cdrom directory. This was
  done to help ensure that the user is only presented with only one cdrom
  interface, the interface defined in \cdromh.
  
  \cdrom\ drives are specific enough (\ie, different from other
  block-devices such as floppy or hard disc drives), to define a set
  of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
  These operations are different from the classical block-device file
  operations, $<block-device>_fops$.
  
  The routines for the \UCD\ interface level are implemented in the file
  \cdromc. In this file, the \UCD\ interfaces with the kernel as a block
  device by registering the following general $struct\ file_operations$:
  $$
  \halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
  struct& file_operations\ cdrom_fops = \{\hidewidth\cr
          &NULL,                  & lseek \cr
          &block_read,            & read---general block-dev read \cr
          &block_write,           & write---general block-dev write \cr
          &NULL,                  & readdir \cr
          &NULL,                  & select \cr
          &cdrom_ioctl,           & ioctl \cr
          &NULL,                  & mmap \cr
          &cdrom_open,            & open \cr
          &cdrom_release,         & release \cr
          &NULL,                  & fsync \cr
          &NULL,                  & fasync \cr
          &cdrom_media_changed,   & media change \cr
          &NULL                   & revalidate \cr
  \};\cr
  }
  $$ 
  
  Every active \cdrom\ device shares this $struct$. The routines
  declared above are all implemented in \cdromc, since this file is the
  place where the behavior of all \cdrom-devices is defined and
  standardized. The actual interface to the various types of \cdrom\ 
  hardware is still performed by various low-level \cdrom-device
  drivers. These routines simply implement certain {\em capabilities\/}
  that are common to all \cdrom\ (and really, all removable-media
  devices).
  
  Registration of a low-level \cdrom\ device driver is now done through
  the general routines in \cdromc, not through the Virtual File System
  (VFS) any more. The interface implemented in \cdromc\ is carried out
  through two general structures that contain information about the
  capabilities of the driver, and the specific drives on which the
  driver operates. The structures are:
  \begin{description}
  \item[$cdrom_device_ops$] 
    This structure contains information about the low-level driver for a
    \cdrom\ device. This structure is conceptually connected to the major
    number of the device (although some drivers may have different
    major numbers, as is the case for the IDE driver).
  \item[$cdrom_device_info$] 
    This structure contains information about a particular \cdrom\ drive,
    such as its device name, speed, etc. This structure is conceptually
    connected to the minor number of the device.
  \end{description}
  
  Registering a particular \cdrom\ drive with the \UCD\ is done by the
  low-level device driver though a call to:
  $$register_cdrom(struct\ cdrom_device_info * <device>_info)  
  $$
  The device information structure, $<device>_info$, contains all the
  information needed for the kernel to interface with the low-level
  \cdrom\ device driver. One of the most important entries in this
  structure is a pointer to the $cdrom_device_ops$ structure of the
  low-level driver.
  
  The device operations structure, $cdrom_device_ops$, contains a list
  of pointers to the functions which are implemented in the low-level
  device driver. When \cdromc\ accesses a \cdrom\ device, it does it
  through the functions in this structure. It is impossible to know all
  the capabilities of future \cdrom\ drives, so it is expected that this
  list may need to be expanded from time to time as new technologies are
  developed. For example, CD-R and CD-R/W drives are beginning to become
  popular, and support will soon need to be added for them. For now, the
  current $struct$ is:
  $$
  \halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
    $/*$ \rm# $*/$\hfil\cr
  struct& cdrom_device_ops\ \{ \hidewidth\cr
    &int& (* open)(struct\ cdrom_device_info *, int)\cr
    &void& (* release)(struct\ cdrom_device_info *);\cr 
    &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr     
    &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr 
    &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
    &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
    &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
    &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
    &int& (* get_last_session) (struct\ cdrom_device_info *, 
          struct\ cdrom_multisession *{});\cr
    &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
    &int& (* reset)(struct\ cdrom_device_info *);\cr
    &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
          void *{});\cr 
    &int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int, 
          unsigned\ long);\cr
  
  oalign{\medskip}
    &const\ int& capability;& capability flags \cr
    &int& n_minors;& number of active minor devices \cr
  \};\cr
  }
  $$
  When a low-level device driver implements one of these capabilities,
  it should add a function pointer to this $struct$. When a particular
  function is not implemented, however, this $struct$ should contain a
  NULL instead. The $capability$ flags specify the capabilities of the
  \cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
  is registered with the \UCD. The value $n_minors$ should be a positive
  value indicating the number of minor devices that are supported by
  the low-level device driver, normally~1. Although these two variables
  are `informative' rather than `operational,' they are included in
  $cdrom_device_ops$ because they describe the capability of the {\em
  driver\/} rather than the {\em drive}. Nomenclature has always been
  difficult in computer programming.
  
  Note that most functions have fewer parameters than their
  $blkdev_fops$ counterparts. This is because very little of the
  information in the structures $inode$ and $file$ is used. For most
  drivers, the main parameter is the $struct$ $cdrom_device_info$, from
  which the major and minor number can be extracted. (Most low-level
  \cdrom\ drivers don't even look at the major and minor number though,
  since many of them only support one device.) This will be available
  through $dev$ in $cdrom_device_info$ described below.
  
  The drive-specific, minor-like information that is registered with
  \cdromc, currently contains the following fields:
  $$
  \halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
    $/*$ \rm# $*/$\hfil\cr
  struct& cdrom_device_info\ \{ \hidewidth\cr
    & struct\ cdrom_device_ops *& ops;& device operations for this major\cr
    & struct\ cdrom_device_info *& next;& next device_info for this major\cr
    & void *&  handle;& driver-dependent data\cr
  
  oalign{\medskip}
    & kdev_t&  dev;& device number (incorporates minor)\cr
    & int& mask;& mask of capability: disables them \cr
    & int& speed;& maximum speed for reading data \cr
    & int& capacity;& number of discs in a jukebox \cr
  
  oalign{\medskip}
    &int& options : 30;& options flags \cr
    &unsigned& mc_flags : 2;& media-change buffer flags \cr
    & int& use_count;& number of times device is opened\cr
    & char& name[20];& name of the device type\cr
  \}\cr
  }$$
  Using this $struct$, a linked list of the registered minor devices is
  built, using the $next$ field. The device number, the device operations
  struct and specifications of properties of the drive are stored in this
  structure.
  
  The $mask$ flags can be used to mask out some of the capabilities listed
  in $ops\to capability$, if a specific drive doesn't support a feature
  of the driver. The value $speed$ specifies the maximum head-rate of the
  drive, measured in units of normal audio speed (176\,kB/sec raw data or
  150\,kB/sec file system data). The value $n_discs$ should reflect the
  number of discs the drive can hold simultaneously, if it is designed
  as a juke-box, or otherwise~1. The parameters are declared $const$
  because they describe properties of the drive, which don't change after
  registration.
  
  A few registers contain variables local to the \cdrom\ drive. The
  flags $options$ are used to specify how the general \cdrom\ routines
  should behave. These various flags registers should provide enough
  flexibility to adapt to the different users' wishes (and {\em not\/} the
  `arbitrary' wishes of the author of the low-level device driver, as is
  the case in the old scheme). The register $mc_flags$ is used to buffer
  the information from $media_changed()$ to two separate queues. Other
  data that is specific to a minor drive, can be accessed through $handle$,
  which can point to a data structure specific to the low-level driver.
  The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
  initialized.
  
  The intermediate software layer that \cdromc\ forms will perform some
  additional bookkeeping. The use count of the device (the number of
  processes that have the device opened) is registered in $use_count$. The
  function $cdrom_ioctl()$ will verify the appropriate user-memory regions
  for read and write, and in case a location on the CD is transferred,
  it will `sanitize' the format by making requests to the low-level
  drivers in a standard format, and translating all formats between the
  user-software and low level drivers. This relieves much of the drivers'
  memory checking and format checking and translation. Also, the necessary
  structures will be declared on the program stack.
  
  The implementation of the functions should be as defined in the
  following sections. Two functions {\em must\/} be implemented, namely
  $open()$ and $release()$. Other functions may be omitted, their
  corresponding capability flags will be cleared upon registration.
  Generally, a function returns zero on success and negative on error. A
  function call should return only after the command has completed, but of
  course waiting for the device should not use processor time.
  
  \subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
  
  $Open()$ should try to open the device for a specific $purpose$, which
  can be either:
  \begin{itemize}
  \item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
  user commands {\tt {dd}} or {\tt {cat}}.  
  \item[1] Open for $ioctl$ commands, as done by audio-CD playing
  programs.
  \end{itemize}
  Notice that any strategic code (closing tray upon $open()$, etc.)\ is
  done by the calling routine in \cdromc, so the low-level routine
  should only be concerned with proper initialization, such as spinning
  up the disc, etc. % and device-use count
  
  
  \subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
  
  
  Device-specific actions should be taken such as spinning down the device.
  However, strategic actions such as ejection of the tray, or unlocking
  the door, should be left over to the general routine $cdrom_release()$.
  This is the only function returning type $void$.
  
  \subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
  \label{drive status}
  
  The function $drive_status$, if implemented, should provide
  information on the status of the drive (not the status of the disc,
  which may or may not be in the drive). If the drive is not a changer,
  $slot_nr$ should be ignored. In \cdromh\ the possibilities are listed: 
  $$
  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
  CDS_NO_INFO& no information available\cr
  CDS_NO_DISC& no disc is inserted, tray is closed\cr
  CDS_TRAY_OPEN& tray is opened\cr
  CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
  CDS_DISC_OK& a disc is loaded and everything is fine\cr
  }
  $$
  
  \subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
  
  This function is very similar to the original function in $struct\ 
  file_operations$. It returns 1 if the medium of the device $cdi\to
  dev$ has changed since the last call, and 0 otherwise. The parameter
  $disc_nr$ identifies a specific slot in a juke-box, it should be
  ignored for single-disc drives.  Note that by `re-routing' this
  function through $cdrom_media_changed()$, we can implement separate
  queues for the VFS and a new $ioctl()$ function that can report device
  changes to software (\eg, an auto-mounting daemon).
  
  \subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
  
  This function, if implemented, should control the tray movement. (No
  other function should control this.) The parameter $position$ controls
  the desired direction of movement:
  \begin{itemize}
  \item[0] Close tray
  \item[1] Open tray
  \end{itemize}
  This function returns 0 upon success, and a non-zero value upon
  error. Note that if the tray is already in the desired position, no
  action need be taken, and the return value should be 0. 
  
  \subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
  
  This function (and no other code) controls locking of the door, if the
  drive allows this. The value of $lock$ controls the desired locking
  state:
  \begin{itemize}
  \item[0] Unlock door, manual opening is allowed
  \item[1] Lock door, tray cannot be ejected manually
  \end{itemize}
  This function returns 0 upon success, and a non-zero value upon
  error. Note that if the door is already in the requested state, no
  action need be taken, and the return value should be 0. 
  
  \subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
  
  Some \cdrom\ drives are capable of changing their head-speed. There
  are several reasons for changing the speed of a \cdrom\ drive. Badly
  pressed \cdrom s may benefit from less-than-maximum head rate. Modern
  \cdrom\ drives can obtain very high head rates (up to $24\times$ is
  common).  It has been reported that these drives can make reading
  errors at these high speeds, reducing the speed can prevent data loss
  in these circumstances.  Finally, some of these drives can
  make an annoyingly loud noise, which a lower speed may reduce. %Finally,
  %although the audio-low-pass filters probably aren't designed for it,
  %more than real-time playback of audio might be used for high-speed
  %copying of audio tracks.
  
  This function specifies the speed at which data is read or audio is
  played back. The value of $speed$ specifies the head-speed of the
  drive, measured in units of standard cdrom speed (176\,kB/sec raw data
  or 150\,kB/sec file system data). So to request that a \cdrom\ drive
  operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
  with $speed=2$. The special value `0' means `auto-selection', \ie,
  maximum data-rate or real-time audio rate. If the drive doesn't have
  this `auto-selection' capability, the decision should be made on the
  current disc loaded and the return value should be positive. A negative
  return value indicates an error.
  
  \subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
  
  If the drive can store multiple discs (a juke-box) this function
  will perform disc selection. It should return the number of the
  selected disc on success, a negative value on error. Currently, only
  the ide-cd driver supports this functionality.
  
  \subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\
    cdrom_multisession * ms_info)$}
  
  This function should implement the old corresponding $ioctl()$. For
  device $cdi\to dev$, the start of the last session of the current disc
  should be returned in the pointer argument $ms_info$. Note that
  routines in \cdromc\ have sanitized this argument: its requested
  format will {\em always\/} be of the type $CDROM_LBA$ (linear block
  addressing mode), whatever the calling software requested. But
  sanitization goes even further: the low-level implementation may
  return the requested information in $CDROM_MSF$ format if it wishes so
  (setting the $ms_info\rightarrow addr_format$ field appropriately, of
  course) and the routines in \cdromc\ will make the transformation if
  necessary. The return value is 0 upon success.
  
  \subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
    cdrom_mcn * mcn)$}
  
  Some discs carry a `Media Catalog Number' (MCN), also called
  `Universal Product Code' (UPC). This number should reflect the number
  that is generally found in the bar-code on the product. Unfortunately,
  the few discs that carry such a number on the disc don't even use the
  same format. The return argument to this function is a pointer to a
  pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
  expected as a 13-character string, terminated by a null-character.
  
  \subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
  
  This call should perform a hard-reset on the drive (although in
  circumstances that a hard-reset is necessary, a drive may very well not
  listen to commands anymore). Preferably, control is returned to the
  caller only after the drive has finished resetting. If the drive is no
  longer listening, it may be wise for the underlying low-level cdrom
  driver to time out.
  
  \subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
    int\ cmd, void * arg)$}
  
  Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
  implemented by the routines described above, and hence the function
  $cdrom_ioctl$ will use those. However, most $ioctl$s deal with
  audio-control. We have decided to leave these to be accessed through a
  single function, repeating the arguments $cmd$ and $arg$. Note that
  the latter is of type $void*{}$, rather than $unsigned\ long\
  int$. The routine $cdrom_ioctl()$ does do some useful things,
  though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
  Seconds, Frames) for all audio calls. It also verifies the memory
  location of $arg$, and reserves stack-memory for the argument. This
  makes implementation of the $audio_ioctl()$ much simpler than in the
  old driver scheme. For example, you may look up the function
  $cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
  this documentation. 
  
  An unimplemented ioctl should return $-ENOSYS$, but a harmless request
  (\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
  errors should be according to the standards, whatever they are. When
  an error is returned by the low-level driver, the \UCD\ tries whenever
  possible to return the error code to the calling program. (We may decide
  to sanitize the return value in $cdrom_ioctl()$ though, in order to
  guarantee a uniform interface to the audio-player software.)
  
  \subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\
    cmd, unsigned\ long\ arg)$}
  
  Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
  they are introduced to service some capabilities of certain drives. In
  fact, there are 6 different $ioctl$s for reading data, either in some
  particular kind of format, or audio data. Not many drives support
  reading audio tracks as data, I believe this is because of protection
  of copyrights of artists. Moreover, I think that if audio-tracks are
  supported, it should be done through the VFS and not via $ioctl$s. A
  problem here could be the fact that audio-frames are 2352 bytes long,
  so either the audio-file-system should ask for 75264 bytes at once
  (the least common multiple of 512 and 2352), or the drivers should
  bend their backs to cope with this incoherence (to which I would be
  opposed).  Furthermore, it is very difficult for the hardware to find
  the exact frame boundaries, since there are no synchronization headers
  in audio frames.  Once these issues are resolved, this code should be
  standardized in \cdromc.
  
  Because there are so many $ioctl$s that seem to be introduced to
  satisfy certain drivers,\footnote{Is there software around that
    actually uses these? I'd be interested!} any `non-standard' $ioctl$s
  are routed through the call $dev_ioctl()$. In principle, `private'
  $ioctl$s should be numbered after the device's major number, and not
  the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
  non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2,
    CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK,
    CDROMPLAY\-BLK and CDROM\-READALL}.
  
  
  \subsection{\cdrom\ capabilities}
  \label{capability}
  
  Instead of just implementing some $ioctl$ calls, the interface in
  \cdromc\ supplies the possibility to indicate the {\em capabilities\/}
  of a \cdrom\ drive. This can be done by ORing any number of
  capability-constants that are defined in \cdromh\ at the registration
  phase. Currently, the capabilities are any of:
  $$
  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
  CDC_CLOSE_TRAY& can close tray by software control\cr
  CDC_OPEN_TRAY& can open tray\cr
  CDC_LOCK& can lock and unlock the door\cr
  CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
  CDC_SELECT_DISC& drive is juke-box\cr
  CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
  CDC_MCN& can read Media Catalog Number\cr
  CDC_MEDIA_CHANGED& can report if disc has changed\cr
  CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
  CDC_RESET& hard reset device\cr
  CDC_IOCTLS& driver has non-standard ioctls\cr
  CDC_DRIVE_STATUS& driver implements drive status\cr
  }
  $$
  The capability flag is declared $const$, to prevent drivers from
  accidentally tampering with the contents. The capability fags actually
  inform \cdromc\ of what the driver can do. If the drive found
  by the driver does not have the capability, is can be masked out by
  the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
  driver has implemented the code for loading and ejecting \cdrom's, and
  hence its corresponding flags in $capability$ will be set. But a SCSI
  \cdrom\ drive might be a caddy system, which can't load the tray, and
  hence for this drive the $cdrom_device_info$ struct will have set
  the $CDC_CLOSE_TRAY$ bit in $mask$.
  
  In the file \cdromc\ you will encounter many constructions of the type
  $$\it
  if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask 
     \mathrel{\&} CDC_<capability>) \ldots
  $$
  There is no $ioctl$ to set the mask\dots The reason is that
  I think it is better to control the {\em behavior\/} rather than the
  {\em capabilities}.
  
  \subsection{Options}
  
  A final flag register controls the {\em behavior\/} of the \cdrom\
  drives, in order to satisfy different users' wishes, hopefully
  independently of the ideas of the respective author who happened to
  have made the drive's support available to the \linux\ community. The
  current behavior options are:
  $$
  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
  CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
  CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
  CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
   purpose for $open()$\cr
  CDO_LOCK& try to lock door if device is opened\cr
  CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
  }
  $$
  
  The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
  CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
  interface and software standards. Before you protest, there are two
  new $ioctl$s implemented in \cdromc, that allow you to control the
  behavior by software. These are:
  $$
  \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
  CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
  CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
  }
  $$
  One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
  newsection we explain what the need for this option is.
  
  A software package {\tt setcd}, available from the Debian distribution
  and {\tt sunsite.unc.edu}, allows user level control of these flags. 
  
  
  ewsection{The need to know the purpose of opening the \cdrom\ device}
  
  Traditionally, Unix devices can be used in two different `modes',
  either by reading/writing to the device file, or by issuing
  controlling commands to the device, by the device's $ioctl()$
  call. The problem with \cdrom\ drives, is that they can be used for
  two entirely different purposes. One is to mount removable
  file systems, \cdrom s, the other is to play audio CD's. Audio commands
  are implemented entirely through $ioctl$s, presumably because the
  first implementation (SUN?) has been such. In principle there is
  nothing wrong with this, but a good control of the `CD player' demands
  that the device can {\em always\/} be opened in order to give the
  $ioctl$ commands, regardless of the state the drive is in. 
  
  On the other hand, when used as a removable-media disc drive (what the
  original purpose of \cdrom s is) we would like to make sure that the
  disc drive is ready for operation upon opening the device. In the old
  scheme, some \cdrom\ drivers don't do any integrity checking, resulting
  in a number of i/o errors reported by the VFS to the kernel when an
  attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
  particularly elegant way to find out that there is no \cdrom\ inserted;
  it more-or-less looks like the old IBM-PC trying to read an empty floppy
  drive for a couple of seconds, after which the system complains it
  can't read from it. Nowadays we can {\em sense\/} the existence of a
  removable medium in a drive, and we believe we should exploit that
  fact. An integrity check on opening of the device, that verifies the
  availability of a \cdrom\ and its correct type (data), would be
  desirable.
  
  These two ways of using a \cdrom\ drive, principally for data and
  secondarily for playing audio discs, have different demands for the
  behavior of the $open()$ call. Audio use simply wants to open the
  device in order to get a file handle which is needed for issuing
  $ioctl$ commands, while data use wants to open for correct and
  reliable data transfer. The only way user programs can indicate what
  their {\em purpose\/} of opening the device is, is through the $flags$
  parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
  implemented (some drivers implement checking for write-related flags,
  but this is not strictly necessary if the device file has correct
  permission flags). Most option flags simply don't make sense to
  \cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and
  $O_SYNC$ have no meaning to a \cdrom. 
  
  We therefore propose to use the flag $O_NONBLOCK$ to indicate
  that the device is opened just for issuing $ioctl$
  commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
  subsequent calls to the device don't cause the calling process to
  wait. We could interpret this as ``don't wait until someone has
  inserted some valid data-\cdrom.'' Thus, our proposal of the
  implementation for the $open()$ call for \cdrom s is:
  \begin{itemize}
  \item If no other flags are set than $O_RDONLY$, the device is opened
  for data transfer, and the return value will be 0 only upon successful
  initialization of the transfer. The call may even induce some actions
  on the \cdrom, such as closing the tray.  
  \item If the option flag $O_NONBLOCK$ is set, opening will always be
  successful, unless the whole device doesn't exist. The drive will take
  no actions whatsoever. 
  \end{itemize}
  
  \subsection{And what about standards?}
  
  You might hesitate to accept this proposal as it comes from the
  \linux\ community, and not from some standardizing institute. What
  about SUN, SGI, HP and all those other Unix and hardware vendors?
  Well, these companies are in the lucky position that they generally
  control both the hardware and software of their supported products,
  and are large enough to set their own standard. They do not have to
  deal with a dozen or more different, competing hardware
  configurations.\footnote{Incidentally, I think that SUN's approach to
  mounting \cdrom s is very good in origin: under Solaris a
  volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
  {/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
  further and have {\em every\/} \cdrom\ on the local area network be
  mounted at the similar location, \ie, no matter in which particular
  machine you insert a \cdrom, it will always appear at the same
  position in the directory tree, on every system. When I wanted to
  implement such a user-program for \linux, I came across the
  differences in behavior of the various drivers, and the need for an
  $ioctl$ informing about media changes.}
  
  We believe that using $O_NONBLOCK$ to indicate that a device is being opened
  for $ioctl$ commands only can be easily introduced in the \linux\
  community. All the CD-player authors will have to be informed, we can
  even send in our own patches to the programs. The use of $O_NONBLOCK$
  has most likely no influence on the behavior of the CD-players on
  other operating systems than \linux. Finally, a user can always revert
  to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
  CDO_USE_FFLAGS)$. 
  
  \subsection{The preferred strategy of $open()$}
  
  The routines in \cdromc\ are designed in such a way that run-time
  configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
  can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
  modes of operation can be set:
  \begin{description}
  \item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
  is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
  future.) If the device is not yet opened by any other process, and if
  the device is being opened for data ($O_NONBLOCK$ is not set) and the
  tray is found to be open, an attempt to close the tray is made. Then,
  it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
  set, that it contains tracks of type `data mode 1.' Only if all tests
  are passed is the return value zero. The door is locked to prevent file
  system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
  set), no actions are taken and a value of 0 will be returned. 
  \item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This
  mimics the behavior of the current sbpcd-driver. The option flags are
  ignored, the tray is closed on the first open, if necessary. Similarly,
  the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
  it is automatically ejected, such that the user can replace it.
  \end{description} 
  We hope that these option can convince everybody (both driver
  maintainers and user program developers) to adopt the new \cdrom\
  driver scheme and option flag interpretation.
  
  
  ewsection{Description of routines in \cdromc}
  
  Only a few routines in \cdromc\ are exported to the drivers. In this
  new section we will discuss these, as well as the functions that `take
  over' the \cdrom\ interface to the kernel. The header file belonging
  to \cdromc\ is called \cdromh. Formerly, some of the contents of this
  file were placed in the file {\tt {ucdrom.h}}, but this file has now been
  merged back into \cdromh.
  
  \subsection{$Struct\ file_operations\ cdrom_fops$}
  
  The contents of this structure were described in section~\ref{cdrom.c}.
  A pointer to this structure is assigned to the $fops$ field
  of the $struct gendisk$.
  
  \subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
  
  This function is used in about the same way one registers $cdrom_fops$
  with the kernel, the device operations and information structures,
  as described in section~\ref{cdrom.c}, should be registered with the
  \UCD:
  $$
  register_cdrom(\&<device>_info));
  $$
  This function returns zero upon success, and non-zero upon
  failure. The structure $<device>_info$ should have a pointer to the
  driver's $<device>_dops$, as in 
  $$
  \vbox{\halign{&$#$\hfil\cr
  struct\ &cdrom_device_info\ <device>_info = \{\cr
  & <device>_dops;\cr
  &\ldots\cr
  \}\cr
  }}$$
  Note that a driver must have one static structure, $<device>_dops$, while
  it may have as many structures $<device>_info$ as there are minor devices
  active. $Register_cdrom()$ builds a linked list from these. 
  
  \subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
  
  Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
  the minor device from the list. If it was the last registered minor for
  the low-level driver, this disconnects the registered device-operation
  routines from the \cdrom\ interface. This function returns zero upon
  success, and non-zero upon failure.
  
  \subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
  
  This function is not called directly by the low-level drivers, it is
  listed in the standard $cdrom_fops$. If the VFS opens a file, this
  function becomes active. A strategy is implemented in this routine,
  taking care of all capabilities and options that are set in the
  $cdrom_device_ops$ connected to the device. Then, the program flow is
  transferred to the device_dependent $open()$ call.
  
  \subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
  *fp)$}
  
  This function implements the reverse-logic of $cdrom_open()$, and then
  calls the device-dependent $release()$ routine. When the use-count has
  reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
  and $invalidate_buffers(dev)$.
  
  
  \subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
  unsigned\ int\ cmd, unsigned\ long\ arg)$}
  \label{cdrom-ioctl}
  
  This function handles all the standard $ioctl$ requests for \cdrom\
  devices in a uniform way. The different calls fall into three
  categories: $ioctl$s that can be directly implemented by device
  operations, ones that are routed through the call $audio_ioctl()$, and
  the remaining ones, that are presumable device-dependent. Generally, a
  negative return value indicates an error.
  
  \subsubsection{Directly implemented $ioctl$s}
  \label{ioctl-direct}
  
  The following `old' \cdrom-$ioctl$s are implemented by directly
  calling device-operations in $cdrom_device_ops$, if implemented and
  not masked:
  \begin{description}
  \item[CDROMMULTISESSION] Requests the last session on a \cdrom.
  \item[CDROMEJECT] Open tray. 
  \item[CDROMCLOSETRAY] Close tray.
  \item[CDROMEJECT_SW] If $arg
  ot=0$, set behavior to auto-close (close
  tray on first open) and auto-eject (eject on last release), otherwise
  set behavior to non-moving on $open()$ and $release()$ calls.
  \item[CDROM_GET_MCN] Get the Media Catalog Number from a CD.
  \end{description}
  
  \subsubsection{$Ioctl$s routed through $audio_ioctl()$}
  \label{ioctl-audio}
  
  The following set of $ioctl$s are all implemented through a call to
  the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
  allocation are performed in $cdrom_ioctl()$, and also sanitization of
  address format ($CDROM_LBA$/$CDROM_MSF$) is done.
  \begin{description}
  \item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
  cdrom_subchnl *{}$.
  \item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type
  $struct\ cdrom_tochdr *{}$. 
  \item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and
  specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
  \item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
  Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
  \item[CDROMPLAYTRKIND] Play audio fragment in track-index format
  delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
  \item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
  cdrom_volctrl *{}$.
  \item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
  cdrom_volctrl *{}$.
  \item[CDROMSTART] Spin up disc.
  \item[CDROMSTOP] Stop playback of audio fragment.
  \item[CDROMPAUSE] Pause playback of audio fragment.
  \item[CDROMRESUME] Resume playing.
  \end{description}
  
  \subsubsection{New $ioctl$s in \cdromc}
  
  The following $ioctl$s have been introduced to allow user programs to
  control the behavior of individual \cdrom\ devices. New $ioctl$
  commands can be identified by the underscores in their names.
  \begin{description}
  \item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
  option flag register after modification. Use  $arg = \rm0$ for reading
  the current flags.
  \item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns
    the option flag register after modification.
  \item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as
    by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or
    150\,kB/sec file system data). The value 0 means `auto-select', \ie,
    play audio discs at real time and data discs at maximum speed. The value
    $arg$ is checked against the maximum head rate of the drive found in the
    $cdrom_dops$.
  \item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box.
    First disc is numbered 0. The number $arg$ is checked against the
    maximum number of discs in the juke-box found in the $cdrom_dops$.
  \item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since
    the last call. Note that calls to $cdrom_media_changed$ by the VFS
    are treated by an independent queue, so both mechanisms will detect
    a media change once. For juke-boxes, an extra argument $arg$
    specifies the slot for which the information is given. The special
    value $CDSL_CURRENT$ requests that information about the currently
    selected slot be returned.
  \item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to
    $drive_status()$. Return values are defined in section~\ref{drive
     status}. Note that this call doesn't return information on the
    current playing activity of the drive; this can be polled through an
    $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument
    $arg$ specifies the slot for which (possibly limited) information is
    given. The special value $CDSL_CURRENT$ requests that information
    about the currently selected slot be returned.
  \item[CDROM_DISC_STATUS] Returns the type of the disc currently in the
    drive.  It should be viewed as a complement to $CDROM_DRIVE_STATUS$.
    This $ioctl$ can provide \emph {some} information about the current
    disc that is inserted in the drive.  This functionality used to be
    implemented in the low level drivers, but is now carried out
    entirely in \UCD.
    
    The history of development of the CD's use as a carrier medium for
    various digital information has lead to many different disc types.
    This $ioctl$ is useful only in the case that CDs have \emph {only
      one} type of data on them.  While this is often the case, it is
    also very common for CDs to have some tracks with data, and some
    tracks with audio.  Because this is an existing interface, rather
    than fixing this interface by changing the assumptions it was made
    under, thereby breaking all user applications that use this
    function, the \UCD\ implements this $ioctl$ as follows: If the CD in
    question has audio tracks on it, and it has absolutely no CD-I, XA,
    or data tracks on it, it will be reported as $CDS_AUDIO$.  If it has
    both audio and data tracks, it will return $CDS_MIXED$.  If there
    are no audio tracks on the disc, and if the CD in question has any
    CD-I tracks on it, it will be reported as $CDS_XA_2_2$.  Failing
    that, if the CD in question has any XA tracks on it, it will be
    reported as $CDS_XA_2_1$.  Finally, if the CD in question has any
    data tracks on it, it will be reported as a data CD ($CDS_DATA_1$).
  
    This $ioctl$ can return:
    $$
    \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
      CDS_NO_INFO& no information available\cr
      CDS_NO_DISC& no disc is inserted, or tray is opened\cr
      CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr
      CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr
      CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr
      CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324  user bytes)\cr
      CDS_MIXED& mixed audio/data disc\cr
      }
    $$
    For some information concerning frame layout of the various disc
    types, see a recent version of \cdromh.
  
  \item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a
    juke-box. 
  \item[CDROMRESET] Reset the drive. 
  \item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the
    drive. Refer to section \ref{capability} for more information on
    these flags.
  \item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$
    unlocks the door, any other value locks it.
  \item[CDROM_DEBUG] Turns on debugging info. Only root is allowed
    to do this. Same semantics as CDROM_LOCKDOOR.
  \end{description}
  
  \subsubsection{Device dependent $ioctl$s}
  
  Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
  if implemented. No memory allocation or verification is carried out. 
  
  
  ewsection{How to update your driver}
  
  \begin{enumerate}
  \item Make a backup of your current driver. 
  \item Get hold of the files \cdromc\ and \cdromh, they should be in
    the directory tree that came with this documentation.
  \item Make sure you include \cdromh.
  \item Change the 3rd argument of $register_blkdev$ from
  $\&<your-drive>_fops$ to $\&cdrom_fops$. 
  \item Just after that line, add the following to register with the \UCD:
    $$register_cdrom(\&<your-drive>_info);$$
    Similarly, add a call to $unregister_cdrom()$ at the appropriate place.
  \item Copy an example of the device-operations $struct$ to your
    source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all
    entries to names corresponding to your driver, or names you just
    happen to like. If your driver doesn't support a certain function,
    make the entry $NULL$. At the entry $capability$ you should list all
    capabilities your driver currently supports. If your driver
    has a capability that is not listed, please send me a message.
  \item Copy the $cdrom_device_info$ declaration from the same example
    driver, and modify the entries according to your needs. If your
    driver dynamically determines the capabilities of the hardware, this
    structure should also be declared dynamically. 
  \item Implement all functions in your $<device>_dops$ structure,
    according to prototypes listed in \cdromh, and specifications given
    in section~\ref{cdrom.c}. Most likely you have already implemented
    the code in a large part, and you will almost certainly need to adapt the
    prototype and return values.
  \item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and
    change the prototype a little. Remove entries listed in the first
    part in section~\ref{cdrom-ioctl}, if your code was OK, these are
    just calls to the routines you adapted in the previous step.
  \item You may remove all remaining memory checking code in the
    $audio_ioctl()$ function that deals with audio commands (these are
    listed in the second part of section~\ref{cdrom-ioctl}). There is no
    need for memory allocation either, so most $case$s in the $switch$
    statement look similar to:
    $$
    case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\ 
    cdrom_tocentry *{})\ arg\bigr);
    $$
  \item All remaining $ioctl$ cases must be moved to a separate
    function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that
    memory checking and allocation must be kept in this code!
  \item Change the prototypes of $<device>_open()$ and
    $<device>_release()$, and remove any strategic code (\ie, tray
    movement, door locking, etc.).
  \item Try to recompile the drivers. We advise you to use modules, both
    for {\tt {cdrom.o}} and your driver, as debugging is much easier this
    way.
  \end{enumerate} 
  
  
  ewsection{Thanks}
  
  Thanks to all the people involved.  First, Erik Andersen, who has
  taken over the torch in maintaining \cdromc\ and integrating much
  \cdrom-related code in the 2.1-kernel.  Thanks to Scott Snyder and
  Gerd Knorr, who were the first to implement this interface for SCSI
  and IDE-CD drivers and added many ideas for extension of the data
  structures relative to kernel~2.0.  Further thanks to Heiko Ei{\sz}feldt,
  Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
  Kroll, the \linux\ \cdrom\ device driver developers who were kind
  enough to give suggestions and criticisms during the writing. Finally
  of course, I want to thank Linus Torvalds for making this possible in
  the first place.
  
  \vfill
  $ \version\ $
  \eject
  \end{document}