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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<title>Core MTD routines</title>
</head>
<body bgcolor="white">
<h1>Core MTD routines</h1>
<UL>
<LI><A NAME="add_mtd_device">
<TT>int add_mtd_device(struct mtd_info *mtd);</TT></A></LI>
<LI><A NAME="del_mtd_device">
<TT>int del_mtd_device(struct mtd_info *mtd);</TT></A></LI>
</UL>
<P>These routines are called by the hardware driver to register and
unregister the device with the MTD subsystem. Each routine
returns zero on success, or -ERRNO on failure.</P>
<UL>
<LI><TT>struct mtd_info *get_mtd_device(struct mtd_info* mtd, int
num);</TT></LI>
<LI><TT>void put_mtd_device(struct mtd_info *mtd);</TT></LI>
</UL>
<P>These routines manipulate the use counts of the MTD devices. An
MTD device <B>must</B> be locked with <TT>get_mtd_device</TT> before
its <TT>struct mtd_info</TT> is dereferenced anywhere outside a
notifier <TT>add</TT> function.</P>
<P><TT>get_mtd_device()</TT> is used to lock devices into memory so that
they cannot be unloaded. If invoked with <TT>mtd == NULL</TT>, it will
return the MTD device with minor number <TT>num</TT>. If invoked with
<TT>num == -1</TT>, it will scan the internal <TT>mtd_table</TT> and
return the device with its <TT>struct mtd_info</TT> at location
<TT>mtd</TT>. If both <TT>num</TT> and <TT>mtd</TT> are specified,
<TT>get_mtd_device</TT> will return successfully only if the entry
at location <TT>num</TT> in the <TT>mtd_table</TT> has its <TT>struct
mtd_info</TT> at <TT>mtd</TT>.</P>
<P>If the requested device has been removed, or if the arguments do
not match, or if the locking fails, then <TT>get_mtd_device</TT> returns
<TT>NULL</TT>. If all is successful, it returns the address of the
<TT>struct mtd_info</TT> for the locked MTD device.</P>
<P><TT>put_mtd_device()</TT> is used to unlock the device so that it
may subsequently be removed.</P>
<UL>
<LI><TT>struct mtd_info *__get_mtd_device(struct mtd_info* mtd, int
num);</TT></LI>
</UL>
<P>This works in a similar fashion to get_mtd_device(), except that
it does not perform the locking. It can be used internally by users
to obtain MTD devices by number when they know that they have already
locked the device in question. It is provided for use by the mtdblock
module, and it is not expected to be used anywhere else.</P>
<UL>
<LI><A NAME="register_mtd_user">
<TT>int register_mtd_user (struct mtd_notifier *new);</TT></A></LI>
<LI><A NAME="unregister_mtd_user">
<TT>int unregister_mtd_user (struct mtd_notifier *old);</TT></A></LI>
</UL>
<P>These routines are called by the <I>user</I> modules, such as the FTL
filesystem, which wish to be notified of the addition or removal of
physical devices, so they can check for the existence of a filesystem
on the device and present or remove the appropriate interface to the user.
</P>
<P>They return zero on success, or -ERRNO on failure.</P>
<P>The <TT>struct mtd_notifier</TT> is a simple linked list entry:</P>
<A NAME="mtd_notifier"></A>
<PRE>
struct mtd_notifier {
void (*add)(struct mtd_info *mtd);
void (*remove)(struct mtd_info *mtd);
struct mtd_notifier *next;
};
</PRE>
<P>Upon calling <TT>register_mtd_user</TT>, the <TT>add</TT> function of
the user will be called for any driver already present in the system.
The <TT>add</TT> function will then be called to notify the user of the
addition of any further MTD drivers to the system.</P>
<P>Similarly, the <TT>remove</TT> function will be called whenever a
driver is removed from the system, and upon calling
<TT>unregister_mtd_user</TT>, the <TT>remove</TT> function will be called
for any devices which are still present in the system.
</P>
<P>The <TT>add</TT> and <TT>remove</TT> functions may sleep, and may
call other functions of the MTD device.</P>
<P><B>NB:</B> Outside the <TT>add</TT> routine, the user may <B>not</B>
dereference the <TT>struct mtd_info</TT> about which they have been
notified unless they first use <TT>get_mtd_device()</TT> to check
that it still exists and increase its use count.</P>
<P>Also note that there is currently no exclusive locking of devices -
they may be accessed simultaneously by multiple <I>user</I> modules.
An allocation system based on the Linux 2.3 resource trees may be
implemented at a later date.</P>
<hr>
<address><a href="mailto:dwmw2@infradead.org">David Woodhouse</a></address>
$Id: core.html,v 1.2 2000/05/03 11:44:50 dwmw2 Exp $
</body>
</html>
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