+++ /dev/null
-<?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>
+++ /dev/null
-/*
- * procfs_example.c: an example proc interface
- *
- * Copyright (C) 2001, Erik Mouw (mouw@nl.linux.org)
- *
- * This file accompanies the procfs-guide in the Linux kernel
- * source. Its main use is to demonstrate the concepts and
- * functions described in the guide.
- *
- * This software has been developed while working on the LART
- * computing board (http://www.lartmaker.nl), which was sponsored
- * by the Delt University of Technology projects Mobile Multi-media
- * Communications and Ubiquitous Communications.
- *
- * This program 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.
- *
- * This program 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.
- *
- * 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
- *
- */
-
-#include <linux/module.h>
-#include <linux/kernel.h>
-#include <linux/init.h>
-#include <linux/proc_fs.h>
-#include <linux/jiffies.h>
-#include <asm/uaccess.h>
-
-
-#define MODULE_VERS "1.0"
-#define MODULE_NAME "procfs_example"
-
-#define FOOBAR_LEN 8
-
-struct fb_data_t {
- char name[FOOBAR_LEN + 1];
- char value[FOOBAR_LEN + 1];
-};
-
-
-static struct proc_dir_entry *example_dir, *foo_file,
- *bar_file, *jiffies_file, *symlink;
-
-
-struct fb_data_t foo_data, bar_data;
-
-
-static int proc_read_jiffies(char *page, char **start,
- off_t off, int count,
- int *eof, void *data)
-{
- int len;
-
- len = sprintf(page, "jiffies = %ld\n",
- jiffies);
-
- return len;
-}
-
-
-static int proc_read_foobar(char *page, char **start,
- off_t off, int count,
- int *eof, void *data)
-{
- int len;
- struct fb_data_t *fb_data = (struct fb_data_t *)data;
-
- /* DON'T DO THAT - buffer overruns are bad */
- len = sprintf(page, "%s = '%s'\n",
- fb_data->name, fb_data->value);
-
- return len;
-}
-
-
-static int proc_write_foobar(struct file *file,
- const char *buffer,
- unsigned long count,
- void *data)
-{
- int len;
- struct fb_data_t *fb_data = (struct fb_data_t *)data;
-
- if(count > FOOBAR_LEN)
- len = FOOBAR_LEN;
- else
- len = count;
-
- if(copy_from_user(fb_data->value, buffer, len))
- return -EFAULT;
-
- fb_data->value[len] = '\0';
-
- return len;
-}
-
-
-static int __init init_procfs_example(void)
-{
- int rv = 0;
-
- /* create directory */
- example_dir = proc_mkdir(MODULE_NAME, NULL);
- if(example_dir == NULL) {
- rv = -ENOMEM;
- goto out;
- }
- /* create jiffies using convenience function */
- jiffies_file = create_proc_read_entry("jiffies",
- 0444, example_dir,
- proc_read_jiffies,
- NULL);
- if(jiffies_file == NULL) {
- rv = -ENOMEM;
- goto no_jiffies;
- }
-
- /* create foo and bar files using same callback
- * functions
- */
- foo_file = create_proc_entry("foo", 0644, example_dir);
- if(foo_file == NULL) {
- rv = -ENOMEM;
- goto no_foo;
- }
-
- strcpy(foo_data.name, "foo");
- strcpy(foo_data.value, "foo");
- foo_file->data = &foo_data;
- foo_file->read_proc = proc_read_foobar;
- foo_file->write_proc = proc_write_foobar;
-
- bar_file = create_proc_entry("bar", 0644, example_dir);
- if(bar_file == NULL) {
- rv = -ENOMEM;
- goto no_bar;
- }
-
- strcpy(bar_data.name, "bar");
- strcpy(bar_data.value, "bar");
- bar_file->data = &bar_data;
- bar_file->read_proc = proc_read_foobar;
- bar_file->write_proc = proc_write_foobar;
-
- /* create symlink */
- symlink = proc_symlink("jiffies_too", example_dir,
- "jiffies");
- if(symlink == NULL) {
- rv = -ENOMEM;
- goto no_symlink;
- }
-
- /* everything OK */
- printk(KERN_INFO "%s %s initialised\n",
- MODULE_NAME, MODULE_VERS);
- return 0;
-
-no_symlink:
- remove_proc_entry("bar", example_dir);
-no_bar:
- remove_proc_entry("foo", example_dir);
-no_foo:
- remove_proc_entry("jiffies", example_dir);
-no_jiffies:
- remove_proc_entry(MODULE_NAME, NULL);
-out:
- return rv;
-}
-
-
-static void __exit cleanup_procfs_example(void)
-{
- remove_proc_entry("jiffies_too", example_dir);
- remove_proc_entry("bar", example_dir);
- remove_proc_entry("foo", example_dir);
- remove_proc_entry("jiffies", example_dir);
- remove_proc_entry(MODULE_NAME, NULL);
-
- printk(KERN_INFO "%s %s removed\n",
- MODULE_NAME, MODULE_VERS);
-}
-
-
-module_init(init_procfs_example);
-module_exit(cleanup_procfs_example);
-
-MODULE_AUTHOR("Erik Mouw");
-MODULE_DESCRIPTION("procfs examples");
-MODULE_LICENSE("GPL");
projects / mirror_ubuntu-kernels.git / commitdiff