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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<title>MTD internal API documentation - overview</title>
</head>
<body bgcolor="white">
<h1 align="center">MTD internal API documentation - overview</h1>
<H2>Structure</H2>
<P>The MTD system is divided into two types of module:
<I>"users"</I> and <I>"drivers".</I></P>
<P><I>Drivers</I> are the modules which provide raw read/write/erase
access to physical memory devices.</P>
<P><I>Users</I> are the modules which use MTD drivers and provide a
higher-level interface to user-space.</P>
<P>We currently have four 'user'
modules available: FTL, NFTL, JFFS and MTDBLOCK. FTL and NFTL both
provide a pseudo-block device on which a 'normal' filesystem is
placed. JFFS is a filesystem which runs directly on the flash, and
MTDBLOCK performs no translation - just provides a block device
interface directly to the underlying MTD driver.
</P>
<P>Just because I use the word 'module', it doesn't mean that these
have to be loadable modules. You can link them statically into your
kernel.</P>
<H2>Writing a driver module</H2>
<P>Instructions for writing a driver are very simple:</P>
<UL>
<LI>Allocate and populate a <A HREF="mtd_info.html"><TT>struct
mtd_info</TT></A> with information
about your device, and pointers to your access routines.</LI>
<LI>Register it by calling <A HREF="core.html#add_mtd_device">
<TT>add_mtd_device</TT></A></LI>
</UL>
<P>Oh yes - you have to actually write the access routines too, which
have to conform to <A HREF="mtd_info.html#read">the rules</A>.</P>
<H2>Writing a user module</H2>
<P>This is only slightly more complex:</P>
<UL>
<LI>Write a pair of <A HREF="core.html#mtd_notifier">
<TT>notifier</TT></A>
<TT>add</TT> and <TT>remove</TT> functions, which will be called
whenever a driver is added to, or removed from, the system,
respectively.</LI>
<LI>Register them by calling <A HREF="core.html#register_mtd_notifier">
<TT>register_mtd_notifier</TT></A></LI>
</UL>
<P>This <EM>ought</EM> to call your notifier function immediately for
all drivers which are already present in the system. But it doesn't
yet. Currently, drivers scan through calling <TT>get_mtd_device()</TT>
to find previously-loaded drivers. This is bad and will be fixed soon.
</P>
<address><a href="mailto:dwmw2@infradead.org">David Woodhouse</a></address>
$Id: overview.html,v 1.1 2000/03/30 10:38:14 dwmw2 Exp $
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