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diff --git a/Documentation/DocBook/procfs-guide.tmpl b/Documentation/DocBook/procfs-guide.tmpl deleted file mode 100644 index 9eba4b7af73..00000000000 --- a/Documentation/DocBook/procfs-guide.tmpl +++ /dev/null @@ -1,626 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [ -<!ENTITY procfsexample SYSTEM "procfs_example.xml"> -]> - -<book id="LKProcfsGuide"> - <bookinfo> - <title>Linux Kernel Procfs Guide</title> - - <authorgroup> - <author> - <firstname>Erik</firstname> - <othername>(J.A.K.)</othername> - <surname>Mouw</surname> - <affiliation> - <address> - <email>mouw@nl.linux.org</email> - </address> - </affiliation> - </author> - <othercredit> - <contrib> - This software and documentation were written while working on the - LART computing board - (<ulink url="http://www.lartmaker.nl/">http://www.lartmaker.nl/</ulink>), - which was sponsored by the Delt University of Technology projects - Mobile Multi-media Communications and Ubiquitous Communications. - </contrib> - </othercredit> - </authorgroup> - - <revhistory> - <revision> - <revnumber>1.0</revnumber> - <date>May 30, 2001</date> - <revremark>Initial revision posted to linux-kernel</revremark> - </revision> - <revision> - <revnumber>1.1</revnumber> - <date>June 3, 2001</date> - <revremark>Revised after comments from linux-kernel</revremark> - </revision> - </revhistory> - - <copyright> - <year>2001</year> - <holder>Erik Mouw</holder> - </copyright> - - - <legalnotice> - <para> - This documentation is free software; you can redistribute it - and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later - version. - </para> - - <para> - This documentation is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR - PURPOSE. See the GNU General Public License for more details. - </para> - - <para> - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - </para> - - <para> - For more details see the file COPYING in the source - distribution of Linux. - </para> - </legalnotice> - </bookinfo> - - - - - <toc> - </toc> - - - - - <preface id="Preface"> - <title>Preface</title> - - <para> - This guide describes the use of the procfs file system from - within the Linux kernel. The idea to write this guide came up on - the #kernelnewbies IRC channel (see <ulink - url="http://www.kernelnewbies.org/">http://www.kernelnewbies.org/</ulink>), - when Jeff Garzik explained the use of procfs and forwarded me a - message Alexander Viro wrote to the linux-kernel mailing list. I - agreed to write it up nicely, so here it is. - </para> - - <para> - I'd like to thank Jeff Garzik - <email>jgarzik@pobox.com</email> and Alexander Viro - <email>viro@parcelfarce.linux.theplanet.co.uk</email> for their input, - Tim Waugh <email>twaugh@redhat.com</email> for his <ulink - url="http://people.redhat.com/twaugh/docbook/selfdocbook/">Selfdocbook</ulink>, - and Marc Joosen <email>marcj@historia.et.tudelft.nl</email> for - proofreading. - </para> - - <para> - Erik - </para> - </preface> - - - - - <chapter id="intro"> - <title>Introduction</title> - - <para> - The <filename class="directory">/proc</filename> file system - (procfs) is a special file system in the linux kernel. It's a - virtual file system: it is not associated with a block device - but exists only in memory. The files in the procfs are there to - allow userland programs access to certain information from the - kernel (like process information in <filename - class="directory">/proc/[0-9]+/</filename>), but also for debug - purposes (like <filename>/proc/ksyms</filename>). - </para> - - <para> - This guide describes the use of the procfs file system from - within the Linux kernel. It starts by introducing all relevant - functions to manage the files within the file system. After that - it shows how to communicate with userland, and some tips and - tricks will be pointed out. Finally a complete example will be - shown. - </para> - - <para> - Note that the files in <filename - class="directory">/proc/sys</filename> are sysctl files: they - don't belong to procfs and are governed by a completely - different API described in the Kernel API book. - </para> - </chapter> - - - - - <chapter id="managing"> - <title>Managing procfs entries</title> - - <para> - This chapter describes the functions that various kernel - components use to populate the procfs with files, symlinks, - device nodes, and directories. - </para> - - <para> - A minor note before we start: if you want to use any of the - procfs functions, be sure to include the correct header file! - This should be one of the first lines in your code: - </para> - - <programlisting> -#include <linux/proc_fs.h> - </programlisting> - - - - - <sect1 id="regularfile"> - <title>Creating a regular file</title> - - <funcsynopsis> - <funcprototype> - <funcdef>struct proc_dir_entry* <function>create_proc_entry</function></funcdef> - <paramdef>const char* <parameter>name</parameter></paramdef> - <paramdef>mode_t <parameter>mode</parameter></paramdef> - <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - This function creates a regular file with the name - <parameter>name</parameter>, file mode - <parameter>mode</parameter> in the directory - <parameter>parent</parameter>. To create a file in the root of - the procfs, use <constant>NULL</constant> as - <parameter>parent</parameter> parameter. When successful, the - function will return a pointer to the freshly created - <structname>struct proc_dir_entry</structname>; otherwise it - will return <constant>NULL</constant>. <xref - linkend="userland"/> describes how to do something useful with - regular files. - </para> - - <para> - Note that it is specifically supported that you can pass a - path that spans multiple directories. For example - <function>create_proc_entry</function>(<parameter>"drivers/via0/info"</parameter>) - will create the <filename class="directory">via0</filename> - directory if necessary, with standard - <constant>0755</constant> permissions. - </para> - - <para> - If you only want to be able to read the file, the function - <function>create_proc_read_entry</function> described in <xref - linkend="convenience"/> may be used to create and initialise - the procfs entry in one single call. - </para> - </sect1> - - - - - <sect1 id="Creating_a_symlink"> - <title>Creating a symlink</title> - - <funcsynopsis> - <funcprototype> - <funcdef>struct proc_dir_entry* - <function>proc_symlink</function></funcdef> <paramdef>const - char* <parameter>name</parameter></paramdef> - <paramdef>struct proc_dir_entry* - <parameter>parent</parameter></paramdef> <paramdef>const - char* <parameter>dest</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - This creates a symlink in the procfs directory - <parameter>parent</parameter> that points from - <parameter>name</parameter> to - <parameter>dest</parameter>. This translates in userland to - <literal>ln -s</literal> <parameter>dest</parameter> - <parameter>name</parameter>. - </para> - </sect1> - - <sect1 id="Creating_a_directory"> - <title>Creating a directory</title> - - <funcsynopsis> - <funcprototype> - <funcdef>struct proc_dir_entry* <function>proc_mkdir</function></funcdef> - <paramdef>const char* <parameter>name</parameter></paramdef> - <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - Create a directory <parameter>name</parameter> in the procfs - directory <parameter>parent</parameter>. - </para> - </sect1> - - - - - <sect1 id="Removing_an_entry"> - <title>Removing an entry</title> - - <funcsynopsis> - <funcprototype> - <funcdef>void <function>remove_proc_entry</function></funcdef> - <paramdef>const char* <parameter>name</parameter></paramdef> - <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - Removes the entry <parameter>name</parameter> in the directory - <parameter>parent</parameter> from the procfs. Entries are - removed by their <emphasis>name</emphasis>, not by the - <structname>struct proc_dir_entry</structname> returned by the - various create functions. Note that this function doesn't - recursively remove entries. - </para> - - <para> - Be sure to free the <structfield>data</structfield> entry from - the <structname>struct proc_dir_entry</structname> before - <function>remove_proc_entry</function> is called (that is: if - there was some <structfield>data</structfield> allocated, of - course). See <xref linkend="usingdata"/> for more information - on using the <structfield>data</structfield> entry. - </para> - </sect1> - </chapter> - - - - - <chapter id="userland"> - <title>Communicating with userland</title> - - <para> - Instead of reading (or writing) information directly from - kernel memory, procfs works with <emphasis>call back - functions</emphasis> for files: functions that are called when - a specific file is being read or written. Such functions have - to be initialised after the procfs file is created by setting - the <structfield>read_proc</structfield> and/or - <structfield>write_proc</structfield> fields in the - <structname>struct proc_dir_entry*</structname> that the - function <function>create_proc_entry</function> returned: - </para> - - <programlisting> -struct proc_dir_entry* entry; - -entry->read_proc = read_proc_foo; -entry->write_proc = write_proc_foo; - </programlisting> - - <para> - If you only want to use a the - <structfield>read_proc</structfield>, the function - <function>create_proc_read_entry</function> described in <xref - linkend="convenience"/> may be used to create and initialise the - procfs entry in one single call. - </para> - - - - <sect1 id="Reading_data"> - <title>Reading data</title> - - <para> - The read function is a call back function that allows userland - processes to read data from the kernel. The read function - should have the following format: - </para> - - <funcsynopsis> - <funcprototype> - <funcdef>int <function>read_func</function></funcdef> - <paramdef>char* <parameter>buffer</parameter></paramdef> - <paramdef>char** <parameter>start</parameter></paramdef> - <paramdef>off_t <parameter>off</parameter></paramdef> - <paramdef>int <parameter>count</parameter></paramdef> - <paramdef>int* <parameter>peof</parameter></paramdef> - <paramdef>void* <parameter>data</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - The read function should write its information into the - <parameter>buffer</parameter>, which will be exactly - <literal>PAGE_SIZE</literal> bytes long. - </para> - - <para> - The parameter - <parameter>peof</parameter> should be used to signal that the - end of the file has been reached by writing - <literal>1</literal> to the memory location - <parameter>peof</parameter> points to. - </para> - - <para> - The <parameter>data</parameter> - parameter can be used to create a single call back function for - several files, see <xref linkend="usingdata"/>. - </para> - - <para> - The rest of the parameters and the return value are described - by a comment in <filename>fs/proc/generic.c</filename> as follows: - </para> - - <blockquote> - <para> - You have three ways to return data: - </para> - <orderedlist> - <listitem> - <para> - Leave <literal>*start = NULL</literal>. (This is the default.) - Put the data of the requested offset at that - offset within the buffer. Return the number (<literal>n</literal>) - of bytes there are from the beginning of the - buffer up to the last byte of data. If the - number of supplied bytes (<literal>= n - offset</literal>) is - greater than zero and you didn't signal eof - and the reader is prepared to take more data - you will be called again with the requested - offset advanced by the number of bytes - absorbed. This interface is useful for files - no larger than the buffer. - </para> - </listitem> - <listitem> - <para> - Set <literal>*start</literal> to an unsigned long value less than - the buffer address but greater than zero. - Put the data of the requested offset at the - beginning of the buffer. Return the number of - bytes of data placed there. If this number is - greater than zero and you didn't signal eof - and the reader is prepared to take more data - you will be called again with the requested - offset advanced by <literal>*start</literal>. This interface is - useful when you have a large file consisting - of a series of blocks which you want to count - and return as wholes. - (Hack by Paul.Russell@rustcorp.com.au) - </para> - </listitem> - <listitem> - <para> - Set <literal>*start</literal> to an address within the buffer. - Put the data of the requested offset at <literal>*start</literal>. - Return the number of bytes of data placed there. - If this number is greater than zero and you - didn't signal eof and the reader is prepared to - take more data you will be called again with the - requested offset advanced by the number of bytes - absorbed. - </para> - </listitem> - </orderedlist> - </blockquote> - - <para> - <xref linkend="example"/> shows how to use a read call back - function. - </para> - </sect1> - - - - - <sect1 id="Writing_data"> - <title>Writing data</title> - - <para> - The write call back function allows a userland process to write - data to the kernel, so it has some kind of control over the - kernel. The write function should have the following format: - </para> - - <funcsynopsis> - <funcprototype> - <funcdef>int <function>write_func</function></funcdef> - <paramdef>struct file* <parameter>file</parameter></paramdef> - <paramdef>const char* <parameter>buffer</parameter></paramdef> - <paramdef>unsigned long <parameter>count</parameter></paramdef> - <paramdef>void* <parameter>data</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - The write function should read <parameter>count</parameter> - bytes at maximum from the <parameter>buffer</parameter>. Note - that the <parameter>buffer</parameter> doesn't live in the - kernel's memory space, so it should first be copied to kernel - space with <function>copy_from_user</function>. The - <parameter>file</parameter> parameter is usually - ignored. <xref linkend="usingdata"/> shows how to use the - <parameter>data</parameter> parameter. - </para> - - <para> - Again, <xref linkend="example"/> shows how to use this call back - function. - </para> - </sect1> - - - - - <sect1 id="usingdata"> - <title>A single call back for many files</title> - - <para> - When a large number of almost identical files is used, it's - quite inconvenient to use a separate call back function for - each file. A better approach is to have a single call back - function that distinguishes between the files by using the - <structfield>data</structfield> field in <structname>struct - proc_dir_entry</structname>. First of all, the - <structfield>data</structfield> field has to be initialised: - </para> - - <programlisting> -struct proc_dir_entry* entry; -struct my_file_data *file_data; - -file_data = kmalloc(sizeof(struct my_file_data), GFP_KERNEL); -entry->data = file_data; - </programlisting> - - <para> - The <structfield>data</structfield> field is a <type>void - *</type>, so it can be initialised with anything. - </para> - - <para> - Now that the <structfield>data</structfield> field is set, the - <function>read_proc</function> and - <function>write_proc</function> can use it to distinguish - between files because they get it passed into their - <parameter>data</parameter> parameter: - </para> - - <programlisting> -int foo_read_func(char *page, char **start, off_t off, - int count, int *eof, void *data) -{ - int len; - - if(data == file_data) { - /* special case for this file */ - } else { - /* normal processing */ - } - - return len; -} - </programlisting> - - <para> - Be sure to free the <structfield>data</structfield> data field - when removing the procfs entry. - </para> - </sect1> - </chapter> - - - - - <chapter id="tips"> - <title>Tips and tricks</title> - - - - - <sect1 id="convenience"> - <title>Convenience functions</title> - - <funcsynopsis> - <funcprototype> - <funcdef>struct proc_dir_entry* <function>create_proc_read_entry</function></funcdef> - <paramdef>const char* <parameter>name</parameter></paramdef> - <paramdef>mode_t <parameter>mode</parameter></paramdef> - <paramdef>struct proc_dir_entry* <parameter>parent</parameter></paramdef> - <paramdef>read_proc_t* <parameter>read_proc</parameter></paramdef> - <paramdef>void* <parameter>data</parameter></paramdef> - </funcprototype> - </funcsynopsis> - - <para> - This function creates a regular file in exactly the same way - as <function>create_proc_entry</function> from <xref - linkend="regularfile"/> does, but also allows to set the read - function <parameter>read_proc</parameter> in one call. This - function can set the <parameter>data</parameter> as well, like - explained in <xref linkend="usingdata"/>. - </para> - </sect1> - - - - <sect1 id="Modules"> - <title>Modules</title> - - <para> - If procfs is being used from within a module, be sure to set - the <structfield>owner</structfield> field in the - <structname>struct proc_dir_entry</structname> to - <constant>THIS_MODULE</constant>. - </para> - - <programlisting> -struct proc_dir_entry* entry; - -entry->owner = THIS_MODULE; - </programlisting> - </sect1> - - - - - <sect1 id="Mode_and_ownership"> - <title>Mode and ownership</title> - - <para> - Sometimes it is useful to change the mode and/or ownership of - a procfs entry. Here is an example that shows how to achieve - that: - </para> - - <programlisting> -struct proc_dir_entry* entry; - -entry->mode = S_IWUSR |S_IRUSR | S_IRGRP | S_IROTH; -entry->uid = 0; -entry->gid = 100; - </programlisting> - - </sect1> - </chapter> - - - - - <chapter id="example"> - <title>Example</title> - - <!-- be careful with the example code: it shouldn't be wider than - approx. 60 columns, or otherwise it won't fit properly on a page - --> - -&procfsexample; - - </chapter> -</book> |