dm kcopyd: add dm_kcopyd_zero to zero an area

This patch introduces dm_kcopyd_zero() to make it easy to use
kcopyd to write zeros into the requested areas instead
instead of copying.  It is implemented by passing a NULL
copying source to dm_kcopyd_copy().

The forthcoming thin provisioning target uses this.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

2 files changed, 30 insertions, 5 deletions

diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 32ac70861d66..bed444c93d8d 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -66,6 +66,8 @@ struct dm_kcopyd_client {
         struct list_head pages_jobs;
 };
 
+static struct page_list zero_page_list;
+
 static void wake(struct dm_kcopyd_client *kc)
 {
         queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
@@ -254,6 +256,9 @@ int __init dm_kcopyd_init(void)
         if (!_job_cache)
                 return -ENOMEM;
 
+        zero_page_list.next = &zero_page_list;
+        zero_page_list.page = ZERO_PAGE(0);
+
         return 0;
 }
 
@@ -322,7 +327,7 @@ static int run_complete_job(struct kcopyd_job *job)
         dm_kcopyd_notify_fn fn = job->fn;
         struct dm_kcopyd_client *kc = job->kc;
 
-        if (job->pages)
+        if (job->pages && job->pages != &zero_page_list)
                 kcopyd_put_pages(kc, job->pages);
         /*
          * If this is the master job, the sub jobs have already
@@ -484,6 +489,8 @@ static void dispatch_job(struct kcopyd_job *job)
         atomic_inc(&kc->nr_jobs);
         if (unlikely(!job->source.count))
                 push(&kc->complete_jobs, job);
+        else if (job->pages == &zero_page_list)
+                push(&kc->io_jobs, job);
         else
                 push(&kc->pages_jobs, job);
         wake(kc);
@@ -592,14 +599,20 @@ int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
         job->flags = flags;
         job->read_err = 0;
         job->write_err = 0;
-        job->rw = READ;
-
-        job->source = *from;
 
         job->num_dests = num_dests;
         memcpy(&job->dests, dests, sizeof(*dests) * num_dests);
 
-        job->pages = NULL;
+        if (from) {
+                job->source = *from;
+                job->pages = NULL;
+                job->rw = READ;
+        } else {
+                memset(&job->source, 0, sizeof job->source);
+                job->source.count = job->dests[0].count;
+                job->pages = &zero_page_list;
+                job->rw = WRITE;
+        }
 
         job->fn = fn;
         job->context = context;
@@ -617,6 +630,14 @@ int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
 }
 EXPORT_SYMBOL(dm_kcopyd_copy);
 
+int dm_kcopyd_zero(struct dm_kcopyd_client *kc,
+                   unsigned num_dests, struct dm_io_region *dests,
+                   unsigned flags, dm_kcopyd_notify_fn fn, void *context)
+{
+        return dm_kcopyd_copy(kc, NULL, num_dests, dests, flags, fn, context);
+}
+EXPORT_SYMBOL(dm_kcopyd_zero);
+
 void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
                                  dm_kcopyd_notify_fn fn, void *context)
 {
diff --git a/include/linux/dm-kcopyd.h b/include/linux/dm-kcopyd.h
index 5e54458e920f..47d9d376e4e7 100644
--- a/include/linux/dm-kcopyd.h
+++ b/include/linux/dm-kcopyd.h
@@ -57,5 +57,9 @@ void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
                                  dm_kcopyd_notify_fn fn, void *context);
 void dm_kcopyd_do_callback(void *job, int read_err, unsigned long write_err);
 
+int dm_kcopyd_zero(struct dm_kcopyd_client *kc,
+                   unsigned num_dests, struct dm_io_region *dests,
+                   unsigned flags, dm_kcopyd_notify_fn fn, void *context);
+
 #endif  /* __KERNEL__ */
 #endif  /* _LINUX_DM_KCOPYD_H */