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>
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@ -445,6 +445,61 @@ void md_flush_request(mddev_t *mddev, struct bio *bio)
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}
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EXPORT_SYMBOL(md_flush_request);
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/* Support for plugging.
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* This mirrors the plugging support in request_queue, but does not
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* require having a whole queue or request structures.
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* We allocate an md_plug_cb for each md device and each thread it gets
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* plugged on. This links tot the private plug_handle structure in the
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* personality data where we keep a count of the number of outstanding
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* plugs so other code can see if a plug is active.
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*/
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struct md_plug_cb {
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struct blk_plug_cb cb;
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mddev_t *mddev;
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};
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static void plugger_unplug(struct blk_plug_cb *cb)
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{
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struct md_plug_cb *mdcb = container_of(cb, struct md_plug_cb, cb);
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if (atomic_dec_and_test(&mdcb->mddev->plug_cnt))
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md_wakeup_thread(mdcb->mddev->thread);
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kfree(mdcb);
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}
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/* Check that an unplug wakeup will come shortly.
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* If not, wakeup the md thread immediately
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*/
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int mddev_check_plugged(mddev_t *mddev)
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{
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struct blk_plug *plug = current->plug;
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struct md_plug_cb *mdcb;
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if (!plug)
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return 0;
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list_for_each_entry(mdcb, &plug->cb_list, cb.list) {
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if (mdcb->cb.callback == plugger_unplug &&
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mdcb->mddev == mddev) {
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/* Already on the list, move to top */
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if (mdcb != list_first_entry(&plug->cb_list,
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struct md_plug_cb,
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cb.list))
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list_move(&mdcb->cb.list, &plug->cb_list);
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return 1;
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}
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}
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/* Not currently on the callback list */
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mdcb = kmalloc(sizeof(*mdcb), GFP_ATOMIC);
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if (!mdcb)
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return 0;
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mdcb->mddev = mddev;
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mdcb->cb.callback = plugger_unplug;
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atomic_inc(&mddev->plug_cnt);
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list_add(&mdcb->cb.list, &plug->cb_list);
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return 1;
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}
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EXPORT_SYMBOL_GPL(mddev_check_plugged);
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static inline mddev_t *mddev_get(mddev_t *mddev)
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{
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@ -494,6 +549,7 @@ void mddev_init(mddev_t *mddev)
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atomic_set(&mddev->active, 1);
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atomic_set(&mddev->openers, 0);
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atomic_set(&mddev->active_io, 0);
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atomic_set(&mddev->plug_cnt, 0);
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spin_lock_init(&mddev->write_lock);
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atomic_set(&mddev->flush_pending, 0);
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init_waitqueue_head(&mddev->sb_wait);
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@ -179,6 +179,9 @@ struct mddev_s
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int delta_disks, new_level, new_layout;
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int new_chunk_sectors;
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atomic_t plug_cnt; /* If device is expecting
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* more bios soon.
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*/
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struct mdk_thread_s *thread; /* management thread */
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struct mdk_thread_s *sync_thread; /* doing resync or reconstruct */
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sector_t curr_resync; /* last block scheduled */
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@ -508,4 +511,5 @@ extern struct bio *bio_clone_mddev(struct bio *bio, gfp_t gfp_mask,
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mddev_t *mddev);
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extern struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
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mddev_t *mddev);
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extern int mddev_check_plugged(mddev_t *mddev);
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#endif /* _MD_MD_H */
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