1016 lines
50 KiB
TeX
1016 lines
50 KiB
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\documentclass{article}
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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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\newcommand{\newsection}[1]{\newpage\section{#1}}
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\evensidemargin=0pt
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\oddsidemargin=0pt
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\topmargin=-\headheight \advance\topmargin by -\headsep
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\textwidth=15.99cm \textheight=24.62cm % normal A4, 1'' margin
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\def\linux{{\sc Linux}}
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\def\cdrom{{\sc cd-rom}}
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\def\UCD{{\sc Uniform cd-rom Driver}}
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\def\cdromc{{\tt {cdrom.c}}}
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\def\cdromh{{\tt {cdrom.h}}}
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\def\fo{\sl} % foreign words
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\def\ie{{\fo i.e.}}
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\def\eg{{\fo e.g.}}
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\everymath{\it} \everydisplay{\it}
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\catcode `\_=\active \def_{\_\penalty100 }
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\catcode`\<=\active \def<#1>{{\langle\hbox{\rm#1}\rangle}}
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\begin{document}
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\title{A \linux\ \cdrom\ standard}
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\author{David van Leeuwen\\{\normalsize\tt david@ElseWare.cistron.nl}
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\\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}}
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\\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}}
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\date{12 March 1999}
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\maketitle
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\newsection{Introduction}
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\linux\ is probably the Unix-like operating system that supports
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the widest variety of hardware devices. The reasons for this are
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presumably
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\begin{itemize}
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\item
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The large list of hardware devices available for the many platforms
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that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.)
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\item
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The open design of the operating system, such that anybody can write a
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driver for \linux.
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\item
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There is plenty of source code around as examples of how to write a driver.
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\end{itemize}
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The openness of \linux, and the many different types of available
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hardware has allowed \linux\ to support many different hardware devices.
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Unfortunately, the very openness that has allowed \linux\ to support
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all these different devices has also allowed the behavior of each
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device driver to differ significantly from one device to another.
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This divergence of behavior has been very significant for \cdrom\
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devices; the way a particular drive reacts to a `standard' $ioctl()$
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call varies greatly from one device driver to another. To avoid making
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their drivers totally inconsistent, the writers of \linux\ \cdrom\
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drivers generally created new device drivers by understanding, copying,
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and then changing an existing one. Unfortunately, this practice did not
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maintain uniform behavior across all the \linux\ \cdrom\ drivers.
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This document describes an effort to establish Uniform behavior across
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all the different \cdrom\ device drivers for \linux. This document also
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defines the various $ioctl$s, and how the low-level \cdrom\ device
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drivers should implement them. Currently (as of the \linux\ 2.1.$x$
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development kernels) several low-level \cdrom\ device drivers, including
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both IDE/ATAPI and SCSI, now use this Uniform interface.
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When the \cdrom\ was developed, the interface between the \cdrom\ drive
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and the computer was not specified in the standards. As a result, many
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different \cdrom\ interfaces were developed. Some of them had their
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own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
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manufacturers adopted an existing electrical interface and changed
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the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
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adapted their drives to one or more of the already existing electrical
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interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
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most of the `NoName' manufacturers). In cases where a new drive really
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brought its own interface or used its own command set and flow control
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scheme, either a separate driver had to be written, or an existing
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driver had to be enhanced. History has delivered us \cdrom\ support for
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many of these different interfaces. Nowadays, almost all new \cdrom\
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drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
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manufacturer will create a new interface. Even finding drives for the
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old proprietary interfaces is getting difficult.
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When (in the 1.3.70's) I looked at the existing software interface,
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which was expressed through \cdromh, it appeared to be a rather wild
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set of commands and data formats.\footnote{I cannot recollect what
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kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
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latest kernel that I was indirectly involved in.} It seemed that many
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features of the software interface had been added to accommodate the
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capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
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importantly, it appeared that the behavior of the `standard' commands
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was different for most of the different drivers: \eg, some drivers
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close the tray if an $open()$ call occurs when the tray is open, while
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others do not. Some drivers lock the door upon opening the device, to
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prevent an incoherent file system, but others don't, to allow software
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ejection. Undoubtedly, the capabilities of the different drives vary,
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but even when two drives have the same capability their drivers'
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behavior was usually different.
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I decided to start a discussion on how to make all the \linux\ \cdrom\
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drivers behave more uniformly. I began by contacting the developers of
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the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
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encouraged me to write the \UCD\ which this document is intended to
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describe. The implementation of the \UCD\ is in the file \cdromc. This
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driver is intended to be an additional software layer that sits on top
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of the low-level device drivers for each \cdrom\ drive. By adding this
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additional layer, it is possible to have all the different \cdrom\
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devices behave {\em exactly\/} the same (insofar as the underlying
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hardware will allow).
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The goal of the \UCD\ is {\em not\/} to alienate driver developers who
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have not yet taken steps to support this effort. The goal of \UCD\ is
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simply to give people writing application programs for \cdrom\ drives
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{\em one\/} \linux\ \cdrom\ interface with consistent behavior for all
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\cdrom\ devices. In addition, this also provides a consistent interface
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between the low-level device driver code and the \linux\ kernel. Care
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is taken that 100\,\% compatibility exists with the data structures and
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programmer's interface defined in \cdromh. This guide was written to
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help \cdrom\ driver developers adapt their code to use the \UCD\ code
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defined in \cdromc.
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Personally, I think that the most important hardware interfaces are
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the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
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of hardware drop continuously, it is also likely that people may have
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more than one \cdrom\ drive, possibly of mixed types. It is important
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that these drives behave in the same way. In December 1994, one of the
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cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
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drive. In the months that I was busy writing a \linux\ driver for it,
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proprietary drives became obsolete and IDE/ATAPI drives became the
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standard. At the time of the last update to this document (November
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1997) it is becoming difficult to even {\em find} anything less than a
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16 speed \cdrom\ drive, and 24 speed drives are common.
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\newsection{Standardizing through another software level}
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\label{cdrom.c}
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At the time this document was conceived, all drivers directly
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implemented the \cdrom\ $ioctl()$ calls through their own routines. This
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led to the danger of different drivers forgetting to do important things
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like checking that the user was giving the driver valid data. More
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importantly, this led to the divergence of behavior, which has already
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been discussed.
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For this reason, the \UCD\ was created to enforce consistent \cdrom\
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drive behavior, and to provide a common set of services to the various
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low-level \cdrom\ device drivers. The \UCD\ now provides another
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software-level, that separates the $ioctl()$ and $open()$ implementation
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from the actual hardware implementation. Note that this effort has
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made few changes which will affect a user's application programs. The
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greatest change involved moving the contents of the various low-level
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\cdrom\ drivers' header files to the kernel's cdrom directory. This was
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done to help ensure that the user is only presented with only one cdrom
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interface, the interface defined in \cdromh.
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\cdrom\ drives are specific enough (\ie, different from other
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block-devices such as floppy or hard disc drives), to define a set
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of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
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These operations are different from the classical block-device file
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operations, $<block-device>_fops$.
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The routines for the \UCD\ interface level are implemented in the file
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\cdromc. In this file, the \UCD\ interfaces with the kernel as a block
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device by registering the following general $struct\ file_operations$:
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$$
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\halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
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struct& file_operations\ cdrom_fops = \{\hidewidth\cr
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&NULL, & lseek \cr
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&block_read, & read---general block-dev read \cr
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&block_write, & write---general block-dev write \cr
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&NULL, & readdir \cr
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&NULL, & select \cr
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&cdrom_ioctl, & ioctl \cr
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&NULL, & mmap \cr
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&cdrom_open, & open \cr
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&cdrom_release, & release \cr
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&NULL, & fsync \cr
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&NULL, & fasync \cr
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&cdrom_media_changed, & media change \cr
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&NULL & revalidate \cr
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\};\cr
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}
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$$
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Every active \cdrom\ device shares this $struct$. The routines
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declared above are all implemented in \cdromc, since this file is the
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place where the behavior of all \cdrom-devices is defined and
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standardized. The actual interface to the various types of \cdrom\
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hardware is still performed by various low-level \cdrom-device
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drivers. These routines simply implement certain {\em capabilities\/}
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that are common to all \cdrom\ (and really, all removable-media
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devices).
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Registration of a low-level \cdrom\ device driver is now done through
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the general routines in \cdromc, not through the Virtual File System
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(VFS) any more. The interface implemented in \cdromc\ is carried out
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through two general structures that contain information about the
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capabilities of the driver, and the specific drives on which the
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driver operates. The structures are:
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\begin{description}
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\item[$cdrom_device_ops$]
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This structure contains information about the low-level driver for a
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\cdrom\ device. This structure is conceptually connected to the major
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number of the device (although some drivers may have different
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major numbers, as is the case for the IDE driver).
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\item[$cdrom_device_info$]
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This structure contains information about a particular \cdrom\ drive,
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such as its device name, speed, etc. This structure is conceptually
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connected to the minor number of the device.
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\end{description}
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Registering a particular \cdrom\ drive with the \UCD\ is done by the
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low-level device driver though a call to:
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$$register_cdrom(struct\ cdrom_device_info * <device>_info)
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$$
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The device information structure, $<device>_info$, contains all the
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information needed for the kernel to interface with the low-level
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\cdrom\ device driver. One of the most important entries in this
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structure is a pointer to the $cdrom_device_ops$ structure of the
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low-level driver.
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The device operations structure, $cdrom_device_ops$, contains a list
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of pointers to the functions which are implemented in the low-level
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device driver. When \cdromc\ accesses a \cdrom\ device, it does it
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through the functions in this structure. It is impossible to know all
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the capabilities of future \cdrom\ drives, so it is expected that this
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list may need to be expanded from time to time as new technologies are
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developed. For example, CD-R and CD-R/W drives are beginning to become
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popular, and support will soon need to be added for them. For now, the
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current $struct$ is:
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$$
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\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
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$/*$ \rm# $*/$\hfil\cr
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struct& cdrom_device_ops\ \{ \hidewidth\cr
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&int& (* open)(struct\ cdrom_device_info *, int)\cr
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&void& (* release)(struct\ cdrom_device_info *);\cr
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&int& (* drive_status)(struct\ cdrom_device_info *, int);\cr
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&int& (* media_changed)(struct\ cdrom_device_info *, int);\cr
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&int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
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&int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
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&int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
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&int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
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&int& (* get_last_session) (struct\ cdrom_device_info *,
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struct\ cdrom_multisession *{});\cr
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&int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
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&int& (* reset)(struct\ cdrom_device_info *);\cr
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&int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int,
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void *{});\cr
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&int& (* dev_ioctl)(struct\ cdrom_device_info *, unsigned\ int,
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unsigned\ long);\cr
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\noalign{\medskip}
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&const\ int& capability;& capability flags \cr
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\};\cr
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}
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$$
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When a low-level device driver implements one of these capabilities,
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it should add a function pointer to this $struct$. When a particular
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function is not implemented, however, this $struct$ should contain a
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NULL instead. The $capability$ flags specify the capabilities of the
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\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
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is registered with the \UCD.
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Note that most functions have fewer parameters than their
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$blkdev_fops$ counterparts. This is because very little of the
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information in the structures $inode$ and $file$ is used. For most
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drivers, the main parameter is the $struct$ $cdrom_device_info$, from
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which the major and minor number can be extracted. (Most low-level
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\cdrom\ drivers don't even look at the major and minor number though,
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since many of them only support one device.) This will be available
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through $dev$ in $cdrom_device_info$ described below.
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The drive-specific, minor-like information that is registered with
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\cdromc, currently contains the following fields:
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$$
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\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
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$/*$ \rm# $*/$\hfil\cr
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struct& cdrom_device_info\ \{ \hidewidth\cr
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& struct\ cdrom_device_ops *& ops;& device operations for this major\cr
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& struct\ cdrom_device_info *& next;& next device_info for this major\cr
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& void *& handle;& driver-dependent data\cr
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\noalign{\medskip}
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& kdev_t& dev;& device number (incorporates minor)\cr
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& int& mask;& mask of capability: disables them \cr
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& int& speed;& maximum speed for reading data \cr
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& int& capacity;& number of discs in a jukebox \cr
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\noalign{\medskip}
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&int& options : 30;& options flags \cr
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&unsigned& mc_flags : 2;& media-change buffer flags \cr
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& int& use_count;& number of times device is opened\cr
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& char& name[20];& name of the device type\cr
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\}\cr
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}$$
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Using this $struct$, a linked list of the registered minor devices is
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built, using the $next$ field. The device number, the device operations
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struct and specifications of properties of the drive are stored in this
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structure.
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The $mask$ flags can be used to mask out some of the capabilities listed
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in $ops\to capability$, if a specific drive doesn't support a feature
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of the driver. The value $speed$ specifies the maximum head-rate of the
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drive, measured in units of normal audio speed (176\,kB/sec raw data or
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150\,kB/sec file system data). The value $n_discs$ should reflect the
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number of discs the drive can hold simultaneously, if it is designed
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as a juke-box, or otherwise~1. The parameters are declared $const$
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because they describe properties of the drive, which don't change after
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registration.
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A few registers contain variables local to the \cdrom\ drive. The
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flags $options$ are used to specify how the general \cdrom\ routines
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should behave. These various flags registers should provide enough
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flexibility to adapt to the different users' wishes (and {\em not\/} the
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`arbitrary' wishes of the author of the low-level device driver, as is
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the case in the old scheme). The register $mc_flags$ is used to buffer
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the information from $media_changed()$ to two separate queues. Other
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data that is specific to a minor drive, can be accessed through $handle$,
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which can point to a data structure specific to the low-level driver.
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The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
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initialized.
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The intermediate software layer that \cdromc\ forms will perform some
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additional bookkeeping. The use count of the device (the number of
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processes that have the device opened) is registered in $use_count$. The
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function $cdrom_ioctl()$ will verify the appropriate user-memory regions
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for read and write, and in case a location on the CD is transferred,
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it will `sanitize' the format by making requests to the low-level
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drivers in a standard format, and translating all formats between the
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user-software and low level drivers. This relieves much of the drivers'
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memory checking and format checking and translation. Also, the necessary
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structures will be declared on the program stack.
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The implementation of the functions should be as defined in the
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following sections. Two functions {\em must\/} be implemented, namely
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$open()$ and $release()$. Other functions may be omitted, their
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corresponding capability flags will be cleared upon registration.
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Generally, a function returns zero on success and negative on error. A
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function call should return only after the command has completed, but of
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course waiting for the device should not use processor time.
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\subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
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$Open()$ should try to open the device for a specific $purpose$, which
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can be either:
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\begin{itemize}
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\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
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user commands {\tt {dd}} or {\tt {cat}}.
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\item[1] Open for $ioctl$ commands, as done by audio-CD playing
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programs.
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\end{itemize}
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Notice that any strategic code (closing tray upon $open()$, etc.)\ is
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done by the calling routine in \cdromc, so the low-level routine
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should only be concerned with proper initialization, such as spinning
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up the disc, etc. % and device-use count
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\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
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Device-specific actions should be taken such as spinning down the device.
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However, strategic actions such as ejection of the tray, or unlocking
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the door, should be left over to the general routine $cdrom_release()$.
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This is the only function returning type $void$.
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\subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
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\label{drive status}
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The function $drive_status$, if implemented, should provide
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information on the status of the drive (not the status of the disc,
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which may or may not be in the drive). If the drive is not a changer,
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$slot_nr$ should be ignored. In \cdromh\ the possibilities are listed:
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$$
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\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
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CDS_NO_INFO& no information available\cr
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CDS_NO_DISC& no disc is inserted, tray is closed\cr
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CDS_TRAY_OPEN& tray is opened\cr
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CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
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CDS_DISC_OK& a disc is loaded and everything is fine\cr
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}
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$$
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\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
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This function is very similar to the original function in $struct\
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file_operations$. It returns 1 if the medium of the device $cdi\to
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dev$ has changed since the last call, and 0 otherwise. The parameter
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$disc_nr$ identifies a specific slot in a juke-box, it should be
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ignored for single-disc drives. Note that by `re-routing' this
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function through $cdrom_media_changed()$, we can implement separate
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queues for the VFS and a new $ioctl()$ function that can report device
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changes to software (\eg, an auto-mounting daemon).
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\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
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This function, if implemented, should control the tray movement. (No
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other function should control this.) The parameter $position$ controls
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the desired direction of movement:
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\begin{itemize}
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\item[0] Close tray
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\item[1] Open tray
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\end{itemize}
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This function returns 0 upon success, and a non-zero value upon
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error. Note that if the tray is already in the desired position, no
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action need be taken, and the return value should be 0.
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\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
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This function (and no other code) controls locking of the door, if the
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drive allows this. The value of $lock$ controls the desired locking
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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.
|
|
|
|
\newsection{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.
|
|
|
|
\newsection{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 $arg\not=0$, 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.
|
|
|
|
\newsection{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}
|
|
|
|
\newsection{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}
|