[PATCH] Small kernel-hacking.tmpl update

From: John Levon (moz@compsoc.man.ac.uk)
Date: Thu Feb 08 2001 - 08:50:00 EST

I hope this is OK, comments more than welcome

--- Documentation/DocBook/kernel-hacking.tmpl.old Tue Feb 6 20:06:15 2001
+++ Documentation/DocBook/kernel-hacking.tmpl Tue Feb 6 21:14:42 2001
@@ -336,6 +336,11 @@
+ If all your routine does is read or write some parameter, consider
+ implementing a <function>sysctl</function> interface instead.
+ </para>
+ <para>
    Inside the ioctl you're in user context to a process. When a
    error occurs you return a negated errno (see
    <filename class=headerfile>include/linux/errno.h</filename>),
@@ -407,7 +412,7 @@
    Note that some functions may sleep implicitly: common ones are
    the user space access functions (*_user) and memory allocation
- functions without GFP_ATOMIC.
+ functions without <symbol>GFP_ATOMIC</symbol>.
@@ -608,7 +613,8 @@
     for some weird device, you have a problem: it is poorly supported
     in Linux because after some time memory fragmentation in a running
     kernel makes it hard. The best way is to allocate the block early
- in the boot process.
+ in the boot process via the <function>alloc_bootmem()</function>
+ routine.
@@ -631,6 +637,20 @@
+ <sect1 id="routines-udelay">
+ <title><function>udelay()</function>/<function>mdelay()</function>
+ <filename class=headerfile>include/asm/delay.h</filename>
+ <filename class=headerfile>include/linux/delay.h</filename>
+ </title>
+ <para>
+ The <function>udelay()</function> function can be used for small pauses.
+ Do not use large values with <function>udelay()</function> as you risk
+ overflow - the helper function <function>mdelay()</function> is useful
+ here, or even consider <function>schedule_timeout()</function>.
+ </para>
+ </sect1>
   <sect1 id="routines-local-irqs">
     <filename class=headerfile>include/asm/system.h</filename>
@@ -687,8 +707,14 @@
     modules this directive is currently ignored). <type>__exit</type>
     is used to declare a function which is only required on exit: the
     function will be dropped if this file is not compiled as a module.
- See the header file for use.
+ See the header file for use. Note that it makes no sense for a function
+ marked with <type>__init</type> to be exported to modules with
+ <function>EXPORT_SYMBOL()</function> - this will break.
+ <para>
+ Static data structures marked as <type>__initdata</type> must be initialised
+ (as opposed to ordinary static data which is zeroed BSS).
+ </para>
@@ -775,6 +801,21 @@
         return 0;
+ <para>
+ You can often avoid having to deal with these problems by using the
+ <structfield>owner</structfield> field of the
+ <structname>file_operations</structname> structure. Set this field
+ as the macro <symbol>THIS_MODULE</symbol>.
+ </para>
+ <para>
+ For more complicated module unload locking requirements, you can set the
+ <structfield>can_unload</structfield> function pointer to your own routine,
+ which should return <returnvalue>0</returnvalue> if the module is
+ unloadable, or <returnvalue>-EBUSY</returnvalue> otherwise.
+ </para>
@@ -822,6 +863,17 @@
     <returnvalue>-ERESTARTSYS</returnvalue> if a signal is received.
     The <function>wait_event()</function> version ignores signals.
+ <para>
+ Do not use the <function>sleep_on()</function> function family -
+ it is very easy to accidentally introduce races; almost certainly
+ one of the <function>wait_event()</function> family will do, or a
+ loop around <function>schedule_timeout()</function>. If you choose
+ to loop around <function>schedule_timeout()</function> remember
+ you must set the task state (with
+ <function>set_current_state()</function>) on each iteration to avoid
+ busy-looping.
+ </para>
   <sect1 id="queue-waking">
@@ -1212,6 +1264,13 @@
      <filename>MAINTAINERS</filename> means you want to be consulted
      when changes are made to a subsystem, and hear about bugs; it
      implies a more-than-passing commitment to some part of the code.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Finally, don't forget to read <filename>Documentation/SubmittingPatches</filename>
+ and possibly <filename>Documentation/SubmittingDrivers</filename>.

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