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authorLinus Torvalds <torvalds@linux-foundation.org>2011-05-29 11:20:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-05-29 11:20:48 -0700
commitb11b06d90a41766c2d31f0acb8a87aa0f2a7188f (patch)
treebe326cde997bcc38b2a9e0a6d6bc7d7ee7b4cbed
parentf1d1c9fa8f360990e263bdcb73e35ab6fbdc41fe (diff)
parentfa34ce73072f90ecd90dcc43f29d82e70e5f8676 (diff)
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Merge git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-2.6-dm
* git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-2.6-dm: dm kcopyd: return client directly and not through a pointer dm kcopyd: reserve fewer pages dm io: use fixed initial mempool size dm kcopyd: alloc pages from the main page allocator dm kcopyd: add gfp parm to alloc_pl dm kcopyd: remove superfluous page allocation spinlock dm kcopyd: preallocate sub jobs to avoid deadlock dm kcopyd: avoid pointless job splitting dm mpath: do not fail paths after integrity errors dm table: reject devices without request fns dm table: allow targets to support discards internally
-rw-r--r--drivers/md/dm-io.c27
-rw-r--r--drivers/md/dm-kcopyd.c168
-rw-r--r--drivers/md/dm-log.c3
-rw-r--r--drivers/md/dm-mpath.c2
-rw-r--r--drivers/md/dm-raid1.c10
-rw-r--r--drivers/md/dm-snap-persistent.c13
-rw-r--r--drivers/md/dm-snap.c10
-rw-r--r--drivers/md/dm-table.c23
-rw-r--r--include/linux/device-mapper.h6
-rw-r--r--include/linux/dm-io.h3
-rw-r--r--include/linux/dm-kcopyd.h3
11 files changed, 144 insertions, 124 deletions
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 76a5af00a26b..2067288f61f9 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -19,6 +19,8 @@
#define DM_MSG_PREFIX "io"
#define DM_IO_MAX_REGIONS BITS_PER_LONG
+#define MIN_IOS 16
+#define MIN_BIOS 16
struct dm_io_client {
mempool_t *pool;
@@ -41,33 +43,21 @@ struct io {
static struct kmem_cache *_dm_io_cache;
/*
- * io contexts are only dynamically allocated for asynchronous
- * io. Since async io is likely to be the majority of io we'll
- * have the same number of io contexts as bios! (FIXME: must reduce this).
- */
-
-static unsigned int pages_to_ios(unsigned int pages)
-{
- return 4 * pages; /* too many ? */
-}
-
-/*
* Create a client with mempool and bioset.
*/
-struct dm_io_client *dm_io_client_create(unsigned num_pages)
+struct dm_io_client *dm_io_client_create(void)
{
- unsigned ios = pages_to_ios(num_pages);
struct dm_io_client *client;
client = kmalloc(sizeof(*client), GFP_KERNEL);
if (!client)
return ERR_PTR(-ENOMEM);
- client->pool = mempool_create_slab_pool(ios, _dm_io_cache);
+ client->pool = mempool_create_slab_pool(MIN_IOS, _dm_io_cache);
if (!client->pool)
goto bad;
- client->bios = bioset_create(16, 0);
+ client->bios = bioset_create(MIN_BIOS, 0);
if (!client->bios)
goto bad;
@@ -81,13 +71,6 @@ struct dm_io_client *dm_io_client_create(unsigned num_pages)
}
EXPORT_SYMBOL(dm_io_client_create);
-int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
-{
- return mempool_resize(client->pool, pages_to_ios(num_pages),
- GFP_KERNEL);
-}
-EXPORT_SYMBOL(dm_io_client_resize);
-
void dm_io_client_destroy(struct dm_io_client *client)
{
mempool_destroy(client->pool);
diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 1bb73a13ca40..819e37eaaeba 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -27,15 +27,19 @@
#include "dm.h"
+#define SUB_JOB_SIZE 128
+#define SPLIT_COUNT 8
+#define MIN_JOBS 8
+#define RESERVE_PAGES (DIV_ROUND_UP(SUB_JOB_SIZE << SECTOR_SHIFT, PAGE_SIZE))
+
/*-----------------------------------------------------------------
* Each kcopyd client has its own little pool of preallocated
* pages for kcopyd io.
*---------------------------------------------------------------*/
struct dm_kcopyd_client {
- spinlock_t lock;
struct page_list *pages;
- unsigned int nr_pages;
- unsigned int nr_free_pages;
+ unsigned nr_reserved_pages;
+ unsigned nr_free_pages;
struct dm_io_client *io_client;
@@ -67,15 +71,18 @@ static void wake(struct dm_kcopyd_client *kc)
queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
}
-static struct page_list *alloc_pl(void)
+/*
+ * Obtain one page for the use of kcopyd.
+ */
+static struct page_list *alloc_pl(gfp_t gfp)
{
struct page_list *pl;
- pl = kmalloc(sizeof(*pl), GFP_KERNEL);
+ pl = kmalloc(sizeof(*pl), gfp);
if (!pl)
return NULL;
- pl->page = alloc_page(GFP_KERNEL);
+ pl->page = alloc_page(gfp);
if (!pl->page) {
kfree(pl);
return NULL;
@@ -90,41 +97,56 @@ static void free_pl(struct page_list *pl)
kfree(pl);
}
-static int kcopyd_get_pages(struct dm_kcopyd_client *kc,
- unsigned int nr, struct page_list **pages)
+/*
+ * Add the provided pages to a client's free page list, releasing
+ * back to the system any beyond the reserved_pages limit.
+ */
+static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
{
- struct page_list *pl;
-
- spin_lock(&kc->lock);
- if (kc->nr_free_pages < nr) {
- spin_unlock(&kc->lock);
- return -ENOMEM;
- }
-
- kc->nr_free_pages -= nr;
- for (*pages = pl = kc->pages; --nr; pl = pl->next)
- ;
+ struct page_list *next;
- kc->pages = pl->next;
- pl->next = NULL;
+ do {
+ next = pl->next;
- spin_unlock(&kc->lock);
+ if (kc->nr_free_pages >= kc->nr_reserved_pages)
+ free_pl(pl);
+ else {
+ pl->next = kc->pages;
+ kc->pages = pl;
+ kc->nr_free_pages++;
+ }
- return 0;
+ pl = next;
+ } while (pl);
}
-static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
+static int kcopyd_get_pages(struct dm_kcopyd_client *kc,
+ unsigned int nr, struct page_list **pages)
{
- struct page_list *cursor;
+ struct page_list *pl;
+
+ *pages = NULL;
+
+ do {
+ pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY);
+ if (unlikely(!pl)) {
+ /* Use reserved pages */
+ pl = kc->pages;
+ if (unlikely(!pl))
+ goto out_of_memory;
+ kc->pages = pl->next;
+ kc->nr_free_pages--;
+ }
+ pl->next = *pages;
+ *pages = pl;
+ } while (--nr);
- spin_lock(&kc->lock);
- for (cursor = pl; cursor->next; cursor = cursor->next)
- kc->nr_free_pages++;
+ return 0;
- kc->nr_free_pages++;
- cursor->next = kc->pages;
- kc->pages = pl;
- spin_unlock(&kc->lock);
+out_of_memory:
+ if (*pages)
+ kcopyd_put_pages(kc, *pages);
+ return -ENOMEM;
}
/*
@@ -141,13 +163,16 @@ static void drop_pages(struct page_list *pl)
}
}
-static int client_alloc_pages(struct dm_kcopyd_client *kc, unsigned int nr)
+/*
+ * Allocate and reserve nr_pages for the use of a specific client.
+ */
+static int client_reserve_pages(struct dm_kcopyd_client *kc, unsigned nr_pages)
{
- unsigned int i;
+ unsigned i;
struct page_list *pl = NULL, *next;
- for (i = 0; i < nr; i++) {
- next = alloc_pl();
+ for (i = 0; i < nr_pages; i++) {
+ next = alloc_pl(GFP_KERNEL);
if (!next) {
if (pl)
drop_pages(pl);
@@ -157,17 +182,18 @@ static int client_alloc_pages(struct dm_kcopyd_client *kc, unsigned int nr)
pl = next;
}
+ kc->nr_reserved_pages += nr_pages;
kcopyd_put_pages(kc, pl);
- kc->nr_pages += nr;
+
return 0;
}
static void client_free_pages(struct dm_kcopyd_client *kc)
{
- BUG_ON(kc->nr_free_pages != kc->nr_pages);
+ BUG_ON(kc->nr_free_pages != kc->nr_reserved_pages);
drop_pages(kc->pages);
kc->pages = NULL;
- kc->nr_free_pages = kc->nr_pages = 0;
+ kc->nr_free_pages = kc->nr_reserved_pages = 0;
}
/*-----------------------------------------------------------------
@@ -216,16 +242,17 @@ struct kcopyd_job {
struct mutex lock;
atomic_t sub_jobs;
sector_t progress;
-};
-/* FIXME: this should scale with the number of pages */
-#define MIN_JOBS 512
+ struct kcopyd_job *master_job;
+};
static struct kmem_cache *_job_cache;
int __init dm_kcopyd_init(void)
{
- _job_cache = KMEM_CACHE(kcopyd_job, 0);
+ _job_cache = kmem_cache_create("kcopyd_job",
+ sizeof(struct kcopyd_job) * (SPLIT_COUNT + 1),
+ __alignof__(struct kcopyd_job), 0, NULL);
if (!_job_cache)
return -ENOMEM;
@@ -299,7 +326,12 @@ static int run_complete_job(struct kcopyd_job *job)
if (job->pages)
kcopyd_put_pages(kc, job->pages);
- mempool_free(job, kc->job_pool);
+ /*
+ * If this is the master job, the sub jobs have already
+ * completed so we can free everything.
+ */
+ if (job->master_job == job)
+ mempool_free(job, kc->job_pool);
fn(read_err, write_err, context);
if (atomic_dec_and_test(&kc->nr_jobs))
@@ -460,14 +492,14 @@ static void dispatch_job(struct kcopyd_job *job)
wake(kc);
}
-#define SUB_JOB_SIZE 128
static void segment_complete(int read_err, unsigned long write_err,
void *context)
{
/* FIXME: tidy this function */
sector_t progress = 0;
sector_t count = 0;
- struct kcopyd_job *job = (struct kcopyd_job *) context;
+ struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
+ struct kcopyd_job *job = sub_job->master_job;
struct dm_kcopyd_client *kc = job->kc;
mutex_lock(&job->lock);
@@ -498,8 +530,6 @@ static void segment_complete(int read_err, unsigned long write_err,
if (count) {
int i;
- struct kcopyd_job *sub_job = mempool_alloc(kc->job_pool,
- GFP_NOIO);
*sub_job = *job;
sub_job->source.sector += progress;
@@ -511,7 +541,7 @@ static void segment_complete(int read_err, unsigned long write_err,
}
sub_job->fn = segment_complete;
- sub_job->context = job;
+ sub_job->context = sub_job;
dispatch_job(sub_job);
} else if (atomic_dec_and_test(&job->sub_jobs)) {
@@ -531,19 +561,19 @@ static void segment_complete(int read_err, unsigned long write_err,
}
/*
- * Create some little jobs that will do the move between
- * them.
+ * Create some sub jobs to share the work between them.
*/
-#define SPLIT_COUNT 8
-static void split_job(struct kcopyd_job *job)
+static void split_job(struct kcopyd_job *master_job)
{
int i;
- atomic_inc(&job->kc->nr_jobs);
+ atomic_inc(&master_job->kc->nr_jobs);
- atomic_set(&job->sub_jobs, SPLIT_COUNT);
- for (i = 0; i < SPLIT_COUNT; i++)
- segment_complete(0, 0u, job);
+ atomic_set(&master_job->sub_jobs, SPLIT_COUNT);
+ for (i = 0; i < SPLIT_COUNT; i++) {
+ master_job[i + 1].master_job = master_job;
+ segment_complete(0, 0u, &master_job[i + 1]);
+ }
}
int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
@@ -553,7 +583,8 @@ int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
struct kcopyd_job *job;
/*
- * Allocate a new job.
+ * Allocate an array of jobs consisting of one master job
+ * followed by SPLIT_COUNT sub jobs.
*/
job = mempool_alloc(kc->job_pool, GFP_NOIO);
@@ -577,10 +608,10 @@ int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
job->fn = fn;
job->context = context;
+ job->master_job = job;
- if (job->source.count < SUB_JOB_SIZE)
+ if (job->source.count <= SUB_JOB_SIZE)
dispatch_job(job);
-
else {
mutex_init(&job->lock);
job->progress = 0;
@@ -606,17 +637,15 @@ int kcopyd_cancel(struct kcopyd_job *job, int block)
/*-----------------------------------------------------------------
* Client setup
*---------------------------------------------------------------*/
-int dm_kcopyd_client_create(unsigned int nr_pages,
- struct dm_kcopyd_client **result)
+struct dm_kcopyd_client *dm_kcopyd_client_create(void)
{
int r = -ENOMEM;
struct dm_kcopyd_client *kc;
kc = kmalloc(sizeof(*kc), GFP_KERNEL);
if (!kc)
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);
- spin_lock_init(&kc->lock);
spin_lock_init(&kc->job_lock);
INIT_LIST_HEAD(&kc->complete_jobs);
INIT_LIST_HEAD(&kc->io_jobs);
@@ -633,12 +662,12 @@ int dm_kcopyd_client_create(unsigned int nr_pages,
goto bad_workqueue;
kc->pages = NULL;
- kc->nr_pages = kc->nr_free_pages = 0;
- r = client_alloc_pages(kc, nr_pages);
+ kc->nr_reserved_pages = kc->nr_free_pages = 0;
+ r = client_reserve_pages(kc, RESERVE_PAGES);
if (r)
goto bad_client_pages;
- kc->io_client = dm_io_client_create(nr_pages);
+ kc->io_client = dm_io_client_create();
if (IS_ERR(kc->io_client)) {
r = PTR_ERR(kc->io_client);
goto bad_io_client;
@@ -647,8 +676,7 @@ int dm_kcopyd_client_create(unsigned int nr_pages,
init_waitqueue_head(&kc->destroyq);
atomic_set(&kc->nr_jobs, 0);
- *result = kc;
- return 0;
+ return kc;
bad_io_client:
client_free_pages(kc);
@@ -659,7 +687,7 @@ bad_workqueue:
bad_slab:
kfree(kc);
- return r;
+ return ERR_PTR(r);
}
EXPORT_SYMBOL(dm_kcopyd_client_create);
diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index a1f321889676..948e3f4925bf 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -449,8 +449,7 @@ static int create_log_context(struct dm_dirty_log *log, struct dm_target *ti,
lc->io_req.mem.type = DM_IO_VMA;
lc->io_req.notify.fn = NULL;
- lc->io_req.client = dm_io_client_create(dm_div_up(buf_size,
- PAGE_SIZE));
+ lc->io_req.client = dm_io_client_create();
if (IS_ERR(lc->io_req.client)) {
r = PTR_ERR(lc->io_req.client);
DMWARN("couldn't allocate disk io client");
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index a550a057d991..aa4e570c2cb5 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1290,7 +1290,7 @@ static int do_end_io(struct multipath *m, struct request *clone,
if (!error && !clone->errors)
return 0; /* I/O complete */
- if (error == -EOPNOTSUPP || error == -EREMOTEIO)
+ if (error == -EOPNOTSUPP || error == -EREMOTEIO || error == -EILSEQ)
return error;
if (mpio->pgpath)
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 976ad4688afc..9bfd057be686 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -22,8 +22,6 @@
#define DM_MSG_PREFIX "raid1"
#define MAX_RECOVERY 1 /* Maximum number of regions recovered in parallel. */
-#define DM_IO_PAGES 64
-#define DM_KCOPYD_PAGES 64
#define DM_RAID1_HANDLE_ERRORS 0x01
#define errors_handled(p) ((p)->features & DM_RAID1_HANDLE_ERRORS)
@@ -887,7 +885,7 @@ static struct mirror_set *alloc_context(unsigned int nr_mirrors,
return NULL;
}
- ms->io_client = dm_io_client_create(DM_IO_PAGES);
+ ms->io_client = dm_io_client_create();
if (IS_ERR(ms->io_client)) {
ti->error = "Error creating dm_io client";
mempool_destroy(ms->read_record_pool);
@@ -1117,9 +1115,11 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto err_destroy_wq;
}
- r = dm_kcopyd_client_create(DM_KCOPYD_PAGES, &ms->kcopyd_client);
- if (r)
+ ms->kcopyd_client = dm_kcopyd_client_create();
+ if (IS_ERR(ms->kcopyd_client)) {
+ r = PTR_ERR(ms->kcopyd_client);
goto err_destroy_wq;
+ }
wakeup_mirrord(ms);
return 0;
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index 95891dfcbca0..135c2f1fdbfc 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -154,11 +154,6 @@ struct pstore {
struct workqueue_struct *metadata_wq;
};
-static unsigned sectors_to_pages(unsigned sectors)
-{
- return DIV_ROUND_UP(sectors, PAGE_SIZE >> 9);
-}
-
static int alloc_area(struct pstore *ps)
{
int r = -ENOMEM;
@@ -318,8 +313,7 @@ static int read_header(struct pstore *ps, int *new_snapshot)
chunk_size_supplied = 0;
}
- ps->io_client = dm_io_client_create(sectors_to_pages(ps->store->
- chunk_size));
+ ps->io_client = dm_io_client_create();
if (IS_ERR(ps->io_client))
return PTR_ERR(ps->io_client);
@@ -368,11 +362,6 @@ static int read_header(struct pstore *ps, int *new_snapshot)
return r;
}
- r = dm_io_client_resize(sectors_to_pages(ps->store->chunk_size),
- ps->io_client);
- if (r)
- return r;
-
r = alloc_area(ps);
return r;
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index a2d330942cb2..9ecff5f3023a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -40,11 +40,6 @@ static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
#define SNAPSHOT_COPY_PRIORITY 2
/*
- * Reserve 1MB for each snapshot initially (with minimum of 1 page).
- */
-#define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1)
-
-/*
* The size of the mempool used to track chunks in use.
*/
#define MIN_IOS 256
@@ -1116,8 +1111,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto bad_hash_tables;
}
- r = dm_kcopyd_client_create(SNAPSHOT_PAGES, &s->kcopyd_client);
- if (r) {
+ s->kcopyd_client = dm_kcopyd_client_create();
+ if (IS_ERR(s->kcopyd_client)) {
+ r = PTR_ERR(s->kcopyd_client);
ti->error = "Could not create kcopyd client";
goto bad_kcopyd;
}
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index cb8380c9767f..451c3bb176d2 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -362,6 +362,7 @@ static void close_dev(struct dm_dev_internal *d, struct mapped_device *md)
static int device_area_is_invalid(struct dm_target *ti, struct dm_dev *dev,
sector_t start, sector_t len, void *data)
{
+ struct request_queue *q;
struct queue_limits *limits = data;
struct block_device *bdev = dev->bdev;
sector_t dev_size =
@@ -370,6 +371,22 @@ static int device_area_is_invalid(struct dm_target *ti, struct dm_dev *dev,
limits->logical_block_size >> SECTOR_SHIFT;
char b[BDEVNAME_SIZE];
+ /*
+ * Some devices exist without request functions,
+ * such as loop devices not yet bound to backing files.
+ * Forbid the use of such devices.
+ */
+ q = bdev_get_queue(bdev);
+ if (!q || !q->make_request_fn) {
+ DMWARN("%s: %s is not yet initialised: "
+ "start=%llu, len=%llu, dev_size=%llu",
+ dm_device_name(ti->table->md), bdevname(bdev, b),
+ (unsigned long long)start,
+ (unsigned long long)len,
+ (unsigned long long)dev_size);
+ return 1;
+ }
+
if (!dev_size)
return 0;
@@ -1346,7 +1363,8 @@ bool dm_table_supports_discards(struct dm_table *t)
return 0;
/*
- * Ensure that at least one underlying device supports discards.
+ * Unless any target used by the table set discards_supported,
+ * require at least one underlying device to support discards.
* t->devices includes internal dm devices such as mirror logs
* so we need to use iterate_devices here, which targets
* supporting discard must provide.
@@ -1354,6 +1372,9 @@ bool dm_table_supports_discards(struct dm_table *t)
while (i < dm_table_get_num_targets(t)) {
ti = dm_table_get_target(t, i++);
+ if (ti->discards_supported)
+ return 1;
+
if (ti->type->iterate_devices &&
ti->type->iterate_devices(ti, device_discard_capable, NULL))
return 1;
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 32a4423710f5..4427e0454051 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -191,6 +191,12 @@ struct dm_target {
/* Used to provide an error string from the ctr */
char *error;
+
+ /*
+ * Set if this target needs to receive discards regardless of
+ * whether or not its underlying devices have support.
+ */
+ unsigned discards_supported:1;
};
/* Each target can link one of these into the table */
diff --git a/include/linux/dm-io.h b/include/linux/dm-io.h
index 5c9186b93fff..f4b0aa3126f5 100644
--- a/include/linux/dm-io.h
+++ b/include/linux/dm-io.h
@@ -69,8 +69,7 @@ struct dm_io_request {
*
* Create/destroy may block.
*/
-struct dm_io_client *dm_io_client_create(unsigned num_pages);
-int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client);
+struct dm_io_client *dm_io_client_create(void);
void dm_io_client_destroy(struct dm_io_client *client);
/*
diff --git a/include/linux/dm-kcopyd.h b/include/linux/dm-kcopyd.h
index 5db216311695..298d587e349b 100644
--- a/include/linux/dm-kcopyd.h
+++ b/include/linux/dm-kcopyd.h
@@ -25,8 +25,7 @@
* To use kcopyd you must first create a dm_kcopyd_client object.
*/
struct dm_kcopyd_client;
-int dm_kcopyd_client_create(unsigned num_pages,
- struct dm_kcopyd_client **result);
+struct dm_kcopyd_client *dm_kcopyd_client_create(void);
void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc);
/*