dm snapshot: fix header corruption race on invalidation

[deliverable/linux.git] / drivers / md / dm-exception-store.c

/*
 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
 * Copyright (C) 2006-2008 Red Hat GmbH
 *
 * This file is released under the GPL.
 */

#include "dm-exception-store.h"

#include <linux/ctype.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>

#define DM_MSG_PREFIX "snapshot exception stores"

static LIST_HEAD(_exception_store_types);
static DEFINE_SPINLOCK(_lock);

static struct dm_exception_store_type *__find_exception_store_type(const char *name)
{
	struct dm_exception_store_type *type;

	list_for_each_entry(type, &_exception_store_types, list)
		if (!strcmp(name, type->name))
			return type;

	return NULL;
}

static struct dm_exception_store_type *_get_exception_store_type(const char *name)
{
	struct dm_exception_store_type *type;

	spin_lock(&_lock);

	type = __find_exception_store_type(name);

	if (type && !try_module_get(type->module))
		type = NULL;

	spin_unlock(&_lock);

	return type;
}

/*
 * get_type
 * @type_name
 *
 * Attempt to retrieve the dm_exception_store_type by name.  If not already
 * available, attempt to load the appropriate module.
 *
 * Exstore modules are named "dm-exstore-" followed by the 'type_name'.
 * Modules may contain multiple types.
 * This function will first try the module "dm-exstore-<type_name>",
 * then truncate 'type_name' on the last '-' and try again.
 *
 * For example, if type_name was "clustered-shared", it would search
 * 'dm-exstore-clustered-shared' then 'dm-exstore-clustered'.
 *
 * 'dm-exception-store-<type_name>' is too long of a name in my
 * opinion, which is why I've chosen to have the files
 * containing exception store implementations be 'dm-exstore-<type_name>'.
 * If you want your module to be autoloaded, you will follow this
 * naming convention.
 *
 * Returns: dm_exception_store_type* on success, NULL on failure
 */
static struct dm_exception_store_type *get_type(const char *type_name)
{
	char *p, *type_name_dup;
	struct dm_exception_store_type *type;

	type = _get_exception_store_type(type_name);
	if (type)
		return type;

	type_name_dup = kstrdup(type_name, GFP_KERNEL);
	if (!type_name_dup) {
		DMERR("No memory left to attempt load for \"%s\"", type_name);
		return NULL;
	}

	while (request_module("dm-exstore-%s", type_name_dup) ||
	       !(type = _get_exception_store_type(type_name))) {
		p = strrchr(type_name_dup, '-');
		if (!p)
			break;
		p[0] = '\0';
	}

	if (!type)
		DMWARN("Module for exstore type \"%s\" not found.", type_name);

	kfree(type_name_dup);

	return type;
}

static void put_type(struct dm_exception_store_type *type)
{
	spin_lock(&_lock);
	module_put(type->module);
	spin_unlock(&_lock);
}

int dm_exception_store_type_register(struct dm_exception_store_type *type)
{
	int r = 0;

	spin_lock(&_lock);
	if (!__find_exception_store_type(type->name))
		list_add(&type->list, &_exception_store_types);
	else
		r = -EEXIST;
	spin_unlock(&_lock);

	return r;
}
EXPORT_SYMBOL(dm_exception_store_type_register);

int dm_exception_store_type_unregister(struct dm_exception_store_type *type)
{
	spin_lock(&_lock);

	if (!__find_exception_store_type(type->name)) {
		spin_unlock(&_lock);
		return -EINVAL;
	}

	list_del(&type->list);

	spin_unlock(&_lock);

	return 0;
}
EXPORT_SYMBOL(dm_exception_store_type_unregister);

/*
 * Round a number up to the nearest 'size' boundary.  size must
 * be a power of 2.
 */
static ulong round_up(ulong n, ulong size)
{
	size--;
	return (n + size) & ~size;
}

static int set_chunk_size(struct dm_exception_store *store,
			  const char *chunk_size_arg, char **error)
{
	unsigned long chunk_size_ulong;
	char *value;

	chunk_size_ulong = simple_strtoul(chunk_size_arg, &value, 10);
	if (*chunk_size_arg == '\0' || *value != '\0') {
		*error = "Invalid chunk size";
		return -EINVAL;
	}

	if (!chunk_size_ulong) {
		store->chunk_size = store->chunk_mask = store->chunk_shift = 0;
		return 0;
	}

	/*
	 * Chunk size must be multiple of page size.  Silently
	 * round up if it's not.
	 */
	chunk_size_ulong = round_up(chunk_size_ulong, PAGE_SIZE >> 9);

	/* Check chunk_size is a power of 2 */
	if (!is_power_of_2(chunk_size_ulong)) {
		*error = "Chunk size is not a power of 2";
		return -EINVAL;
	}

	/* Validate the chunk size against the device block size */
	if (chunk_size_ulong % (bdev_logical_block_size(store->cow->bdev) >> 9)) {
		*error = "Chunk size is not a multiple of device blocksize";
		return -EINVAL;
	}

	store->chunk_size = chunk_size_ulong;
	store->chunk_mask = chunk_size_ulong - 1;
	store->chunk_shift = ffs(chunk_size_ulong) - 1;

	return 0;
}

int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
			      unsigned *args_used,
			      struct dm_exception_store **store)
{
	int r = 0;
	struct dm_exception_store_type *type = NULL;
	struct dm_exception_store *tmp_store;
	char persistent;

	if (argc < 3) {
		ti->error = "Insufficient exception store arguments";
		return -EINVAL;
	}

	tmp_store = kmalloc(sizeof(*tmp_store), GFP_KERNEL);
	if (!tmp_store) {
		ti->error = "Exception store allocation failed";
		return -ENOMEM;
	}

	persistent = toupper(*argv[1]);
	if (persistent == 'P')
		type = get_type("P");
	else if (persistent == 'N')
		type = get_type("N");
	else {
		ti->error = "Persistent flag is not P or N";
		return -EINVAL;
	}

	if (!type) {
		ti->error = "Exception store type not recognised";
		r = -EINVAL;
		goto bad_type;
	}

	tmp_store->type = type;
	tmp_store->ti = ti;

	r = dm_get_device(ti, argv[0], 0, 0,
			  FMODE_READ | FMODE_WRITE, &tmp_store->cow);
	if (r) {
		ti->error = "Cannot get COW device";
		goto bad_cow;
	}

	r = set_chunk_size(tmp_store, argv[2], &ti->error);
	if (r)
		goto bad_cow;

	r = type->ctr(tmp_store, 0, NULL);
	if (r) {
		ti->error = "Exception store type constructor failed";
		goto bad_ctr;
	}

	*args_used = 3;
	*store = tmp_store;
	return 0;

bad_ctr:
	dm_put_device(ti, tmp_store->cow);
bad_cow:
	put_type(type);
bad_type:
	kfree(tmp_store);
	return r;
}
EXPORT_SYMBOL(dm_exception_store_create);

void dm_exception_store_destroy(struct dm_exception_store *store)
{
	store->type->dtr(store);
	dm_put_device(store->ti, store->cow);
	put_type(store->type);
	kfree(store);
}
EXPORT_SYMBOL(dm_exception_store_destroy);

int dm_exception_store_init(void)
{
	int r;

	r = dm_transient_snapshot_init();
	if (r) {
		DMERR("Unable to register transient exception store type.");
		goto transient_fail;
	}

	r = dm_persistent_snapshot_init();
	if (r) {
		DMERR("Unable to register persistent exception store type");
		goto persistent_fail;
	}

	return 0;

persistent_fail:
	dm_persistent_snapshot_exit();
transient_fail:
	return r;
}

void dm_exception_store_exit(void)
{
	dm_persistent_snapshot_exit();
	dm_transient_snapshot_exit();
}