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Re: [dm-devel] [PATCH 8/8] [dm-cache] cache target



On Tue, Feb 12, 2013 at 03:27:33PM +0000, Alasdair G Kergon wrote:
> updated code taken from the all-caches branch of 
> git://github.com/jthornber/linux-2.6
 
File: dm-cache-policy.c

> #include "dm.h"

> #include <linux/list.h>
Already pulled in via dm.h

> static struct dm_cache_policy_type *__get_policy(const char *name)
> {
> 	struct dm_cache_policy_type *t = __find_policy(name);
> 
> 	if (!t) {

Could we move this up a level and avoid the inverted unlock/lock
(which only seems to confuse automated lock analysis)?
   __find_policy(); if not found, request_module and __find_policy again ?

> 		spin_unlock(&register_lock);
> 		request_module("dm-cache-%s", name);
> 		spin_lock(&register_lock);
> 		t = __find_policy(name);
> 	}

> int dm_cache_policy_register(struct dm_cache_policy_type *type)
> {
> 	int r;
> 
> 	/* One size fits all for now */
> 	if (type->hint_size != 0 && type->hint_size != 4)

This should never happen unless coding error or corruption => DMWARN?

> 		return -EINVAL;


> void dm_cache_policy_destroy(struct dm_cache_policy *p)
> {
> 	struct dm_cache_policy_type *t = p->private;
> 
> 	put_policy(t);

module_put should be AFTER destroy or the code could get unloaded while destroy
is still running?

[Still to check the ref counting is sufficient: to understand why this is
a bit simpler than dm-path-selector which also handles modules plugging into
modules and went through a few iterations fixing ref problems]

> 	p->destroy(p);
> }

Alasdair


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