kernel-ark/drivers/md/dm-exception-store.c
Mikulas Patocka c1cc65caa1 dm snapshot: allow chunk size to be less than page size
Allow the snapshot chunk size to be smaller than the page size
The code is now capable of handling this due to some previous
fixes and enhancements.

As the page size varies between computers, prior to this patch,
the chunk size of a snapshot dictated which machines could read it:
Snapshots created on one machine might not be readable on another.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-10-16 23:18:22 +01:00

300 lines
6.6 KiB
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);
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' ||
chunk_size_ulong > UINT_MAX) {
*error = "Invalid chunk size";
return -EINVAL;
}
if (!chunk_size_ulong) {
store->chunk_size = store->chunk_mask = store->chunk_shift = 0;
return 0;
}
return dm_exception_store_set_chunk_size(store,
(unsigned) chunk_size_ulong,
error);
}
int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
unsigned chunk_size,
char **error)
{
/* Check chunk_size is a power of 2 */
if (!is_power_of_2(chunk_size)) {
*error = "Chunk size is not a power of 2";
return -EINVAL;
}
/* Validate the chunk size against the device block size */
if (chunk_size % (bdev_logical_block_size(store->cow->bdev) >> 9)) {
*error = "Chunk size is not a multiple of device blocksize";
return -EINVAL;
}
if (chunk_size > INT_MAX >> SECTOR_SHIFT) {
*error = "Chunk size is too high";
return -EINVAL;
}
store->chunk_size = chunk_size;
store->chunk_mask = chunk_size - 1;
store->chunk_shift = ffs(chunk_size) - 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_ctr;
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();
}