[PATCH 01/51] ARM: reset: introduce arm_arch_reset function pointer

[Russell King - ARM Linux]

On Sat, Oct 29, 2011 at 02:56:53PM +0100, Will Deacon wrote:
> The only downside is that I have to go over all of the platforms again
> unless I can polish up my Coccinelle-fu. Ho-hum.

Well, I've just given coccinelle a go, and having read all the hype about
it, I'm completely disappointed with it to the extent that I'm going to
uninstall the tool from my system (unless someone can point out what I'm
doing wrong.)

I thought I'd give it a spin on a nice simple change - deleting the
local_irq_disable() calls inside arch_reset() (irqs have already been
disabled by this time):

@@
identifier mode, cmd;
@@

arch_reset(char mode, const char *cmd)
{
...
- local_irq_disable();
...
}

$ spatch -sp_file arch_reset-1.cocci arch/arm/*/include/*/system.h > arch_reset-1.diff

The diff it created contains:

--- arch/arm/mach-ep93xx/include/mach/system.h  2011-03-04 19:52:46.419272878 +0000
+++ /tmp/cocci-output-380-f841cc-system.h       2011-10-31 13:54:52.066705107 +0000
...
--- arch/arm/mach-iop32x/include/mach/system.h  2011-03-04 19:52:46.445272534 +0000
+++ /tmp/cocci-output-380-c0e3f4-system.h       2011-10-31 13:54:52.072705051 +0000
...
--- arch/arm/mach-ixp2000/include/mach/system.h 2011-03-04 19:52:46.449272482 +0000
+++ /tmp/cocci-output-380-467f17-system.h       2011-10-31 13:54:52.079704984 +0000
...

which in total deletes 6 lines.  However, the patch is rejected by
git apply and gnu patch as it stands - it needs the filenames to be
edited to something more reasonable.  So that also takes six edits.

I might as well have used grep and an editor to do the job:

$ files=$(grep -l local_irq_disable arch/arm/*/include/*/system.h)
$ uemacs $files
$ git add $files
$ git commit

And for a more complex task, you're still going to have to mess about
editing filenames.  This seems (to me) to make the tool rather awkward
to use.  On the plus side, for complex changes it does help to make
you look at the generated patch rather than just believing it to be
correct.