md: provide generic support for handling unplug callbacks.
When an md device adds a request to a queue, it can call
mddev_check_plugged.
If this succeeds then we know that the md thread will be woken up
shortly, and ->plug_cnt will be non-zero until then, so some
processing can be delayed.
If it fails, then no unplug callback is expected and the make_request
function needs to do whatever is required to make the request happen.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/md.c b/drivers/md/md.c
index fb11170..6e853c6 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -445,6 +445,61 @@
}
EXPORT_SYMBOL(md_flush_request);
+/* Support for plugging.
+ * This mirrors the plugging support in request_queue, but does not
+ * require having a whole queue or request structures.
+ * We allocate an md_plug_cb for each md device and each thread it gets
+ * plugged on. This links tot the private plug_handle structure in the
+ * personality data where we keep a count of the number of outstanding
+ * plugs so other code can see if a plug is active.
+ */
+struct md_plug_cb {
+ struct blk_plug_cb cb;
+ mddev_t *mddev;
+};
+
+static void plugger_unplug(struct blk_plug_cb *cb)
+{
+ struct md_plug_cb *mdcb = container_of(cb, struct md_plug_cb, cb);
+ if (atomic_dec_and_test(&mdcb->mddev->plug_cnt))
+ md_wakeup_thread(mdcb->mddev->thread);
+ kfree(mdcb);
+}
+
+/* Check that an unplug wakeup will come shortly.
+ * If not, wakeup the md thread immediately
+ */
+int mddev_check_plugged(mddev_t *mddev)
+{
+ struct blk_plug *plug = current->plug;
+ struct md_plug_cb *mdcb;
+
+ if (!plug)
+ return 0;
+
+ list_for_each_entry(mdcb, &plug->cb_list, cb.list) {
+ if (mdcb->cb.callback == plugger_unplug &&
+ mdcb->mddev == mddev) {
+ /* Already on the list, move to top */
+ if (mdcb != list_first_entry(&plug->cb_list,
+ struct md_plug_cb,
+ cb.list))
+ list_move(&mdcb->cb.list, &plug->cb_list);
+ return 1;
+ }
+ }
+ /* Not currently on the callback list */
+ mdcb = kmalloc(sizeof(*mdcb), GFP_ATOMIC);
+ if (!mdcb)
+ return 0;
+
+ mdcb->mddev = mddev;
+ mdcb->cb.callback = plugger_unplug;
+ atomic_inc(&mddev->plug_cnt);
+ list_add(&mdcb->cb.list, &plug->cb_list);
+ return 1;
+}
+EXPORT_SYMBOL_GPL(mddev_check_plugged);
static inline mddev_t *mddev_get(mddev_t *mddev)
{
@@ -494,6 +549,7 @@
atomic_set(&mddev->active, 1);
atomic_set(&mddev->openers, 0);
atomic_set(&mddev->active_io, 0);
+ atomic_set(&mddev->plug_cnt, 0);
spin_lock_init(&mddev->write_lock);
atomic_set(&mddev->flush_pending, 0);
init_waitqueue_head(&mddev->sb_wait);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index fad9022..0b1fd3f 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -179,6 +179,9 @@
int delta_disks, new_level, new_layout;
int new_chunk_sectors;
+ atomic_t plug_cnt; /* If device is expecting
+ * more bios soon.
+ */
struct mdk_thread_s *thread; /* management thread */
struct mdk_thread_s *sync_thread; /* doing resync or reconstruct */
sector_t curr_resync; /* last block scheduled */
@@ -508,4 +511,5 @@
mddev_t *mddev);
extern struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
mddev_t *mddev);
+extern int mddev_check_plugged(mddev_t *mddev);
#endif /* _MD_MD_H */