dm-exception-store.c

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/*
 * 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/module.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 chunk_size;

    if (kstrtouint(chunk_size_arg, 10, &chunk_size)) {
        *error = "Invalid chunk size";
        return -EINVAL;
    }

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

    return dm_exception_store_set_chunk_size(store, chunk_size, 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(dm_snap_cow(store->snap)->bdev) >> 9) ||
        chunk_size %
        (bdev_logical_block_size(dm_snap_origin(store->snap)->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,
                  struct dm_snapshot *snap,
                  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 < 2) {
        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[0]);
    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";
        r = -EINVAL;
        goto bad_type;
    }

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

    tmp_store->type = type;
    tmp_store->snap = snap;

    r = set_chunk_size(tmp_store, argv[1], &ti->error);
    if (r)
        goto bad;

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

    *args_used = 2;
    *store = tmp_store;
    return 0;

bad:
    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);
    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_transient_snapshot_exit();
transient_fail:
    return r;
}

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