linux-kernel - Re: [RFC] __ref annotation of function/data referencing __init/_

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Message-ID: <20080129201245.GA14857@uranus.ravnborg.org>
Date:	Tue, 29 Jan 2008 21:12:45 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [RFC] __ref annotation of function/data referencing __init/__exit

On Tue, Jan 29, 2008 at 08:55:32PM +0100, Jan Engelhardt wrote:
> 
> On Jan 28 2008 22:38, Sam Ravnborg wrote:
> >On Sat, Jan 26, 2008 at 07:44:54PM +0100, Sam Ravnborg wrote:
> >> Today we have the following annotations for functions/data
> >> referencing __init/__exit functions / data:
> >> 
> >> __init_refok for functions
> >> __initdata_refok for data
> >> 
> >> and
> >> _exit_refok for functions
> >> 
> >> To simplify it and to introduce a shorter annotation I
> >> will suggest the following annotation:
> >> 
> >> __ref      <= for functions (code) that
> >>               references __*init / __*exit
> >> __refdata  <= for variables
> >> __refconst <= for const variables
> >>
> >
> >This patch was includedin todays kbuild.git submission
> >as I heard no negative feedback.
> 
> I would like to see some real-world example of __ref*.
> When would you want to "reference" (function pointer?) an __init
> function from outside another __init function?

It replaces the old __init_Refok - so you can just grep for that one.
One obvious example:

init/main.c:static void noinline __init_refok rest_init(void)

Here we jump from the the __init part to the normal operation.

And
static noinline __init_refok
int zone_wait_table_init(struct zone *zone, unsigned long zone_size_pages)
{
       ...
      if (system_state == SYSTEM_BOOTING) {
                zone->wait_table = (wait_queue_head_t *)
                        alloc_bootmem_node(pgdat, alloc_size);

The program logic guarantee that we only call
alloc_bootmem_node when we are in the init phase.
So to silence the warning we added __init_refok that is
now named __ref.

We have plenty of data structures containing pointers to
functions annotated __*init or __*exit.

One that casues a lot of warnings is pci_serial_quirks.

Here we can use the annotation to tell modpost that
the references are OK like this (see __refdata):

static struct pci_serial_quirk pci_serial_quirks[] __refdata = {
	...
                .exit           = __devexit_p(sbs_exit),
        },


thout the annotation modpost would complain about the
reference to sbs_exit because sbs_exit is annotated __devexit.

If you have proposals to improve the commeonts in init.h please let
me know. This seems to confuse a lot of people.

	Sam
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