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Subject[PATCH] procfs guide
Hi,

I got some comments on my procfs guide when I posted it a couple of
days ago, so here is a new version. What's new:

- add revision history (Jonathan Lundel)
- remove_proc_entry() is not recursive (Jonathan Lundel)
- numerous spelling corrections (Marc Joosen)
- /proc/sys files are sysctl, not procfs (John Levon)
- add an implicit .c to .sgml rule to the Makefile (me)
- fixed a too long comment in the example code (me)

The patch is against 2.4.5-ac6, but should apply cleanly to 2.4.5-ac7
as well. Please apply.


Erik

--
J.A.K. (Erik) Mouw, Information and Communication Theory Group, Department
of Electrical Engineering, Faculty of Information Technology and Systems,
Delft University of Technology, PO BOX 5031, 2600 GA Delft, The Netherlands
Phone: +31-15-2783635 Fax: +31-15-2781843 Email: J.A.K.Mouw@its.tudelft.nl
WWW: http://www-ict.its.tudelft.nl/~erik/


Index: Documentation/DocBook/Makefile
===================================================================
RCS file: /home/erik/cvsroot/elinux/Documentation/DocBook/Makefile,v
retrieving revision 1.1.1.30
diff -u -r1.1.1.30 Makefile
--- Documentation/DocBook/Makefile 2001/05/15 12:14:07 1.1.1.30
+++ Documentation/DocBook/Makefile 2001/06/03 21:09:27
@@ -1,7 +1,7 @@
BOOKS := wanbook.sgml z8530book.sgml mcabook.sgml videobook.sgml \
kernel-api.sgml parportbook.sgml kernel-hacking.sgml \
kernel-locking.sgml via-audio.sgml mousedrivers.sgml sis900.sgml \
- deviceiobook.sgml
+ deviceiobook.sgml procfs-guide.sgml

PS := $(patsubst %.sgml, %.ps, $(BOOKS))
PDF := $(patsubst %.sgml, %.pdf, $(BOOKS))
@@ -9,6 +9,7 @@
IMG-parportbook := parport-share.fig parport-multi.fig parport-structure.fig
EPS-parportbook := $(patsubst %.fig, %.eps, $(IMG-parportbook))
JPG-parportbook := $(patsubst %.fig, %.jpeg, $(IMG-parportbook))
+C-procfs-example = procfs_example.sgml

books: $(BOOKS)

@@ -28,6 +29,15 @@
%.jpeg: %.fig
-fig2dev -Ljpeg $< $@

+%.sgml: %.c
+ echo "<programlisting>" > $@
+ expand --tabs=8 < $< | \
+ sed -e "s/&/\\&amp;/g" \
+ -e "s/</\\&lt;/g" \
+ -e "s/>/\\&gt;/g" >> $@
+ echo "</programlisting>" >> $@
+
+
$(TOPDIR)/scripts/docproc:
$(MAKE) -C $(TOPDIR)/scripts docproc

@@ -67,6 +77,9 @@
$(TOPDIR)/scripts/docgen $(TOPDIR)/drivers/media/video/videodev.c \
<videobook.tmpl >videobook.sgml

+procfs-guide.sgml: procfs-guide.tmpl procfs_example.sgml
+ $(TOPDIR)/scripts/docgen < procfs-guide.tmpl >$@
+
APISOURCES := $(TOPDIR)/drivers/media/video/videodev.c \
$(TOPDIR)/arch/i386/kernel/irq.c \
$(TOPDIR)/arch/i386/kernel/mca.c \
@@ -128,6 +141,7 @@
-$(RM) $(BOOKS)
-$(RM) $(DVI) $(AUX) $(TEX) $(LOG) $(OUT)
-$(RM) $(JPG-parportbook) $(EPS-parportbook)
+ -$(RM) $(C-procfs-example)

mrproper: clean
-$(RM) $(PS) $(PDF)
Index: Documentation/DocBook/procfs-guide.tmpl
===================================================================
RCS file: procfs-guide.tmpl
diff -N procfs-guide.tmpl
--- /dev/null Thu Mar 22 14:04:47 2001
+++ Documentation/DocBook/procfs-guide.tmpl Sun Jun 3 23:39:23 2001
@@ -0,0 +1,625 @@
+<!-- -*- sgml -*- -->
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN"[
+<!ENTITY procfsexample SYSTEM "procfs_example.sgml">
+]>
+
+<book id="LKProcfsGuide">
+ <bookinfo>
+ <title>Linux Kernel Procfs Guide</title>
+
+ <authorgroup>
+ <author>
+ <firstname>Erik</firstname>
+ <othername>(J.A.K.)</othername>
+ <surname>Mouw</surname>
+ <affiliation>
+ <orgname>Delft University of Technology</orgname>
+ <orgdiv>Faculty of Information Technology and Systems</orgdiv>
+ <address>
+ <email>J.A.K.Mouw@its.tudelft.nl</email>
+ <pob>PO BOX 5031</pob>
+ <postcode>2600 GA</postcode>
+ <city>Delft</city>
+ <country>The Netherlands</country>
+ </address>
+ </affiliation>
+ </author>
+ </authorgroup>
+
+ <revhistory>
+ <revision>
+ <revnumber>1.0&nbsp;</revnumber>
+ <date>May 30, 2001</date>
+ <revremark>Initial revision posted to linux-kernel</revremark>
+ </revision>
+ <revision>
+ <revnumber>1.1&nbsp;</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>
+ <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@mandrakesoft.com</email> and Alexander Viro
+ <email>viro@math.psu.edu</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>
+ This documentation was written while working on the LART
+ computing board (<ulink
+ url="http://www.lart.tudelft.nl/">http://www.lart.tudelft.nl/</ulink>),
+ which is sponsored by the Mobile Multi-media Communications
+ (<ulink
+ url="http://www.mmc.tudelft.nl/">http://www.mmc.tudelft.nl/</ulink>)
+ and Ubiquitous Communications (<ulink
+ url="http://www.ubicom.tudelft.nl/">http://www.ubicom.tudelft.nl/</ulink>)
+ projects.
+ </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>
+ <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>
+ <title>Creating a device</title>
+
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>struct proc_dir_entry* <function>proc_mknod</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>kdev_t <parameter>rdev</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+
+ <para>
+ Creates a device file <parameter>name</parameter> with mode
+ <parameter>mode</parameter> in the procfs directory
+ <parameter>parent</parameter>. The device file will work on
+ the device <parameter>rdev</parameter>, which can be generated
+ by using the <literal>MKDEV</literal> macro from
+ <literal>linux/kdev_t.h</literal>. The
+ <parameter>mode</parameter> parameter
+ <emphasis>must</emphasis> contain <constant>S_IFBLK</constant>
+ or <constant>S_IFCHR</constant> to create a device
+ node. Compare with userland <literal>mknod
+ --mode=</literal><parameter>mode</parameter>
+ <parameter>name</parameter> <parameter>rdev</parameter>.
+ </para>
+ </sect1>
+
+
+
+
+ <sect1>
+ <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>
+ <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>
+ <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>page</parameter></paramdef>
+ <paramdef>char** <parameter>start</parameter></paramdef>
+ <paramdef>off_t <parameter>off</parameter></paramdef>
+ <paramdef>int <parameter>count</parameter></paramdef>
+ <paramdef>int* <parameter>eof</parameter></paramdef>
+ <paramdef>void* <parameter>data</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+
+ <para>
+ The read function should write its information into the
+ <parameter>page</parameter>. For proper use, the function
+ should start writing at an offset of
+ <parameter>off</parameter> in <parameter>page</parameter> and
+ write at most <parameter>count</parameter> bytes, but because
+ most read functions are quite simple and only return a small
+ amount of information, these two parameters are usually
+ ignored (it breaks pagers like <literal>more</literal> and
+ <literal>less</literal>, but <literal>cat</literal> still
+ works).
+ </para>
+
+ <para>
+ If the <parameter>off</parameter> and
+ <parameter>count</parameter> parameters are properly used,
+ <parameter>eof</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>eof</parameter> points to.
+ </para>
+
+ <para>
+ The parameter <parameter>start</parameter> doesn't seem to be
+ used anywhere in the kernel. 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 <function>read_func</function> function must return the
+ number of bytes written into the <parameter>page</parameter>.
+ </para>
+
+ <para>
+ <xref linkend="example"> shows how to use a read call back
+ function.
+ </para>
+ </sect1>
+
+
+
+
+ <sect1>
+ <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>
+ <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>
+ <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>
Index: Documentation/DocBook/procfs_example.c
===================================================================
RCS file: procfs_example.c
diff -N procfs_example.c
--- /dev/null Thu Mar 22 14:04:47 2001
+++ Documentation/DocBook/procfs_example.c Sun Jun 3 23:09:39 2001
@@ -0,0 +1,249 @@
+/*
+ * procfs_example.c: an example proc interface
+ *
+ * Copyright (C) 2001, Erik Mouw (J.A.K.Mouw@its.tudelft.nl)
+ *
+ * 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.lart.tudelft.nl/), which is
+ * sponsored by the Mobile Multi-media Communications
+ * (http://www.mmc.tudelft.nl/) and Ubiquitous Communications
+ * (http://www.ubicom.tudelft.nl/) projects.
+ *
+ * The author can be reached at:
+ *
+ * Erik Mouw
+ * Information and Communication Theory Group
+ * Faculty of Information Technology and Systems
+ * Delft University of Technology
+ * P.O. Box 5031
+ * 2600 GA Delft
+ * The Netherlands
+ *
+ *
+ * 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/sched.h>
+#include <asm/uaccess.h>
+
+
+#define MODULE_VERSION "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, *tty_device, *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;
+
+ MOD_INC_USE_COUNT;
+
+ len = sprintf(page, "jiffies = %ld\n",
+ jiffies);
+
+ MOD_DEC_USE_COUNT;
+
+ 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;
+
+ MOD_INC_USE_COUNT;
+
+ len = sprintf(page, "%s = '%s'\n",
+ fb_data->name, fb_data->value);
+
+ MOD_DEC_USE_COUNT;
+
+ 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;
+
+ MOD_INC_USE_COUNT;
+
+ if(count > FOOBAR_LEN)
+ len = FOOBAR_LEN;
+ else
+ len = count;
+
+ if(copy_from_user(fb_data->value, buffer, len)) {
+ MOD_DEC_USE_COUNT;
+ return -EFAULT;
+ }
+
+ fb_data->value[len] = '\0';
+
+ MOD_DEC_USE_COUNT;
+
+ 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;
+ }
+
+ example_dir->owner = THIS_MODULE;
+
+ /* 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;
+ }
+
+ jiffies_file->owner = THIS_MODULE;
+
+ /* 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;
+ foo_file->owner = THIS_MODULE;
+
+ 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;
+ bar_file->owner = THIS_MODULE;
+
+ /* create tty device */
+ tty_device = proc_mknod("tty", S_IFCHR | 0666,
+ example_dir, MKDEV(5, 0));
+ if(tty_device == NULL) {
+ rv = -ENOMEM;
+ goto no_tty;
+ }
+
+ tty_device->owner = THIS_MODULE;
+
+ /* create symlink */
+ symlink = proc_symlink("jiffies_too", example_dir,
+ "jiffies");
+ if(symlink == NULL) {
+ rv = -ENOMEM;
+ goto no_symlink;
+ }
+
+ symlink->owner = THIS_MODULE;
+
+ /* everything OK */
+ printk(KERN_INFO "%s %s initialised\n",
+ MODULE_NAME, MODULE_VERSION);
+ return 0;
+
+no_symlink:
+ remove_proc_entry("tty", example_dir);
+no_tty:
+ 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("tty", 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_VERSION);
+}
+
+
+module_init(init_procfs_example);
+module_exit(cleanup_procfs_example);
+
+MODULE_AUTHOR("Erik Mouw");
+MODULE_DESCRIPTION("procfs examples");
+
+EXPORT_NO_SYMBOLS;


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