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proc: remove docbook and example

Browse source 
Example is outdated, it still uses old ->read_proc interfaces and "fb"
example is plain racy.  There are better examples all over the tree.

Docbook itself says almost nothing about /proc and contain quite a number
of simply wrong facts, e.g.  device nodes support.  What it does is
describing at great length interface which are going to be removed.

There are Documentation/filesystems/seq_file.txt in exchange.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Erik Mouw <mouw@nl.linux.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexey Dobriyan 2009-12-15 16:46:59 -08:00 committed by Linus Torvalds
parent 7de3369c14
commit 82c1e49ccb
3 changed files with 3 additions and 841 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

17
Documentation/DocBook/Makefile
View file

@ -8,7 +8,7 @@
DOCBOOKS := z8530book.xml mcabook.xml device-drivers.xml \
kernel-hacking.xml kernel-locking.xml deviceiobook.xml \
procfs-guide.xml writing_usb_driver.xml networking.xml \
writing_usb_driver.xml networking.xml \
kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
@ -65,7 +65,7 @@ KERNELDOC = $(srctree)/scripts/kernel-doc
DOCPROC = $(objtree)/scripts/basic/docproc
XMLTOFLAGS = -m $(srctree)/Documentation/DocBook/stylesheet.xsl
#XMLTOFLAGS += --skip-validation
XMLTOFLAGS += --skip-validation
###
# DOCPROC is used for two purposes:
@ -101,17 +101,6 @@ endif
# Changes in kernel-doc force a rebuild of all documentation
$(BOOKS): $(KERNELDOC)
###
# procfs guide uses a .c file as example code.
# This requires an explicit dependency
C-procfs-example = procfs_example.xml
C-procfs-example2 = $(addprefix $(obj)/,$(C-procfs-example))
$(obj)/procfs-guide.xml: $(C-procfs-example2)
# List of programs to build
##oops, this is a kernel module::hostprogs-y := procfs_example
obj-m += procfs_example.o
# Tell kbuild to always build the programs
always := $(hostprogs-y)
@ -238,7 +227,7 @@ clean-files := $(DOCBOOKS) \
$(patsubst %.xml, %.pdf, $(DOCBOOKS)) \
$(patsubst %.xml, %.html, $(DOCBOOKS)) \
$(patsubst %.xml, %.9, $(DOCBOOKS)) \
$(C-procfs-example) $(index)
$(index)
clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS)) man

626
Documentation/DocBook/procfs-guide.tmpl
View file

@ -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 &lt;linux/proc_fs.h&gt;
</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>

201
Documentation/DocBook/procfs_example.c
View file

@ -1,201 +0,0 @@
/*
* 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");