From a2826aa92e2e14db372eda01d333267258944033 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 14 Dec 2009 12:49:49 +1100 Subject: md: support barrier requests on all personalities. Previously barriers were only supported on RAID1. This is because other levels requires synchronisation across all devices and so needed a different approach. Here is that approach. When a barrier arrives, we send a zero-length barrier to every active device. When that completes - and if the original request was not empty - we submit the barrier request itself (with the barrier flag cleared) and then submit a fresh load of zero length barriers. The barrier request itself is asynchronous, but any subsequent request will block until the barrier completes. The reason for clearing the barrier flag is that a barrier request is allowed to fail. If we pass a non-empty barrier through a striping raid level it is conceivable that part of it could succeed and part could fail. That would be way too hard to deal with. So if the first run of zero length barriers succeed, we assume all is sufficiently well that we send the request and ignore errors in the second run of barriers. RAID5 needs extra care as write requests may not have been submitted to the underlying devices yet. So we flush the stripe cache before proceeding with the barrier. Note that the second set of zero-length barriers are submitted immediately after the original request is submitted. Thus when a personality finds mddev->barrier to be set during make_request, it should not return from make_request until the corresponding per-device request(s) have been queued. That will be done in later patches. Signed-off-by: NeilBrown Reviewed-by: Andre Noll --- drivers/md/md.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'drivers/md/md.h') diff --git a/drivers/md/md.h b/drivers/md/md.h index 87430fe..cb03686 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -292,6 +292,17 @@ struct mddev_s struct mutex bitmap_mutex; struct list_head all_mddevs; + + /* Generic barrier handling. + * If there is a pending barrier request, all other + * writes are blocked while the devices are flushed. + * The last to finish a flush schedules a worker to + * submit the barrier request (without the barrier flag), + * then submit more flush requests. + */ + struct bio *barrier; + atomic_t flush_pending; + struct work_struct barrier_work; }; @@ -432,6 +443,7 @@ extern void md_done_sync(mddev_t *mddev, int blocks, int ok); extern void md_error(mddev_t *mddev, mdk_rdev_t *rdev); extern int mddev_congested(mddev_t *mddev, int bits); +extern void md_barrier_request(mddev_t *mddev, struct bio *bio); extern void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev, sector_t sector, int size, struct page *page); extern void md_super_wait(mddev_t *mddev); -- cgit v1.1