linux-kernel - Re: Problem: plist

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Date:	Wed, 21 Dec 2011 22:51:02 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Monica Puig-Pey <puigpeym@...can.es>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Problem: plist_add undefined!

On Tue, 2011-12-20 at 10:24 +0100, Monica Puig-Pey wrote:
> Hi there,
> 
> As I told in previous posts in this list I'm developing drivers for the
> 
> linux-rt kernel version in Ubuntu 10.04, based on 2.6.31 with rt_preempt 
> patch.
> 
> Currently I'm studying how to use priority lists (linux/plist.h) in a 
> module. I read some pages from the Linux Kernel Development book to 
> learn how linked list work in the kernel.
> 
> I made and easy example, shown below, trying to put three elements, with 
> their priorities, in a plist_head.
> 
> Then, I had two problems:
> 
> * First error:
> 
>    An error is produced when using the MACROs:
>      - PLIST_HEAD_INIT(head, _lock)
>      - PLIST_NODE_INIT(node, __prio)

Right, the macros are for static declarations. Either global variables
or a variable marked as static:

struct plist_head myhead = PLIST_HEAD_INIT(myhead, mylock);

or

int foo() {
	static struct plist_head bar = PLIST_HEAD_INIT(bar, mylock);

	[...]
}

or

struct foo bar = {
	.zoop = PLIST_HEAD_INIT(bar.zoop, mylock),
};


> 
>    it says :
> 
> 
> /home/monica/Escritorio/plists/priolist.c: In function 'init_module': 
> /home/monica/Escritorio/plists/priolist.c:67: error: expected expression 
> before '.' token
> 
> 
>    --> To solve this I used the functions:
> 
> 
> - static inline void plist_head_init(struct plist_head *head, struct 
> spinlock *lock)
> 
> - static inline void plist_node_init(struct plist_node *node, int prio)

Right, for runtime code you must use these.


> 
>    But I still have the problem with the MACRO
> 
> 
> 
> 
> * Second error, problem using plist_add:
> 
>    It says:
> 
> 
> “WARNING: "plist_add" [/home/monica/Escritorio/plists/priolist.ko] 
> undefined! ”

Simple, plist_add() isn't exported to modules.

Hmm, none of the plist functions are. I guess it wouldn't hurt to make
them EXPORT_SYMBOL_GPL()

Maybe we'll do that. Is this just for learning or are you planing on
adding a real GPL module to Linux that uses plists. For learning, it may
not be worth adding these symbols, but if you have a legit reason for
modules to use plists, than I don't see any harm in exporting them.

-- Steve

> 
>    I made the module GPL, I don't know what am I doing wrong.
> 
> Does anybody have an idea what is happening?
> 
> Thanks in advance for any help,
> 
> Cheers,
> 


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