Hi Mikulas,
This patch doesn't apply to 2.6.29.
Probably you are using a pretty older kernel?
Thanks,
Kiyoshi Ueda
On 2009/03/27 15:11 +0900, Mikulas Patocka wrote:
> Barrier support.
>
> Barriers are submitted to a worker thread that issues them in-order.
>
> __split_and_process_bio function is modified that when it sees a barrier
> request, it waits for all pending IO before the request, then submits
> the barrier and waits for it (we must wait, otherwise it could be
> intermixed with following requests).
>
> Errors from the barrier request are recorded in per-device barrier_error
> variable. There may be only one barrier request in progress, so using
> a per-device variable is correct.
>
> The barrier request is converted to non-barrier request when sending it
> to the underlying device.
>
> This patch guarantees correct barrier behavior if the underlying device
> doesn't perform write-back caching. The same requirement existed before
> barriers were supported in dm.
>
> Bottom layer barrier support (sending barriers by target drivers) and
> handling devices with write-back caches will be done in further patches.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> ---
> drivers/md/dm.c | 79 +++++++++++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 61 insertions(+), 18 deletions(-)
>
> Index: linux-2.6.29-rc8-devel/drivers/md/dm.c
> ===================================================================
> --- linux-2.6.29-rc8-devel.orig/drivers/md/dm.c 2009-03-27 06:51:29.000000000 +0100
> +++ linux-2.6.29-rc8-devel/drivers/md/dm.c 2009-03-27 06:51:33.000000000 +0100
> @@ -125,6 +125,11 @@ struct mapped_device {
> spinlock_t deferred_lock;
>
> /*
> + * An error from the barrier request currently being processed.
> + */
> + int barrier_error;
> +
> + /*
> * Processing queue (flush/barriers)
> */
> struct workqueue_struct *wq;
> @@ -425,6 +430,10 @@ static void end_io_acct(struct dm_io *io
> part_stat_add(cpu, &dm_disk(md)->part0, ticks[rw], duration);
> part_stat_unlock();
>
> + /*
> + * after this is decremented, the bio must not be touched if it is
> + * barrier bio
> + */
> dm_disk(md)->part0.in_flight = pending =
> atomic_dec_return(&md->pending);
>
> @@ -525,19 +534,29 @@ static void dec_pending(struct dm_io *io
> */
> spin_lock_irqsave(&io->md->deferred_lock, flags);
> if (__noflush_suspending(io->md))
> - bio_list_add(&io->md->deferred, io->bio);
> + bio_list_add_head(&io->md->deferred, io->bio);
> else
> /* noflush suspend was interrupted. */
> io->error = -EIO;
> spin_unlock_irqrestore(&io->md->deferred_lock, flags);
> }
>
> - end_io_acct(io);
> + if (bio_barrier(io->bio)) {
> + /*
> + * There could be just one barrier request, so we use
> + * per-device variable for error reporting is OK.
> + * Note that you can't touch the bio after end_io_acct
> + */
> + io->md->barrier_error = io->error;
> + end_io_acct(io);
> + } else {
> + end_io_acct(io);
>
> - if (io->error != DM_ENDIO_REQUEUE) {
> - trace_block_bio_complete(io->md->queue, io->bio);
> + if (io->error != DM_ENDIO_REQUEUE) {
> + trace_block_bio_complete(io->md->queue, io->bio);
>
> - bio_endio(io->bio, io->error);
> + bio_endio(io->bio, io->error);
> + }
> }
>
> free_io(io->md, io);
> @@ -682,7 +701,7 @@ static struct bio *split_bvec(struct bio
>
> clone->bi_sector = sector;
> clone->bi_bdev = bio->bi_bdev;
> - clone->bi_rw = bio->bi_rw;
> + clone->bi_rw = bio->bi_rw & ~(1 << BIO_RW_BARRIER);
> clone->bi_vcnt = 1;
> clone->bi_size = to_bytes(len);
> clone->bi_io_vec->bv_offset = offset;
> @@ -703,6 +722,7 @@ static struct bio *clone_bio(struct bio
>
> clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
> __bio_clone(clone, bio);
> + clone->bi_rw &= ~(1 << BIO_RW_BARRIER);
> clone->bi_destructor = dm_bio_destructor;
> clone->bi_sector = sector;
> clone->bi_idx = idx;
> @@ -823,7 +843,10 @@ static void __split_and_process_bio(stru
>
> ci.map = dm_get_table(md);
> if (unlikely(!ci.map)) {
> - bio_io_error(bio);
> + if (!bio_barrier(bio))
> + bio_io_error(bio);
> + else
> + md->barrier_error = -EIO;
> return;
> }
>
> @@ -907,15 +930,6 @@ static int dm_request(struct request_que
> struct mapped_device *md = q->queuedata;
> int cpu;
>
> - /*
> - * There is no use in forwarding any barrier request since we can't
> - * guarantee it is (or can be) handled by the targets correctly.
> - */
> - if (unlikely(bio_barrier(bio))) {
> - bio_endio(bio, -EOPNOTSUPP);
> - return 0;
> - }
> -
> down_read(&md->io_lock);
>
> cpu = part_stat_lock();
> @@ -927,7 +941,8 @@ static int dm_request(struct request_que
> * If we're suspended or the thread is processing barriers
> * we have to queue this io for later.
> */
> - if (unlikely(test_bit(DMF_QUEUE_IO_FOR_THREAD, &md->flags))) {
> + if (unlikely(test_bit(DMF_QUEUE_IO_FOR_THREAD, &md->flags)) ||
> + unlikely(bio_barrier(bio))) {
> up_read(&md->io_lock);
>
> if (unlikely(test_bit(DMF_BLOCK_FOR_SUSPEND, &md->flags)) &&
> @@ -1393,6 +1408,12 @@ static int dm_wait_for_completion(struct
> return r;
> }
>
> +static int dm_flush(struct mapped_device *md)
> +{
> + dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
> + return 0;
> +}
> +
> /*
> * Process the deferred bios
> */
> @@ -1415,8 +1436,30 @@ static void dm_wq_work(struct work_struc
> break;
> }
>
> - __split_and_process_bio(md, c);
> + if (!bio_barrier(c))
> + __split_and_process_bio(md, c);
> + else {
> + int error = dm_flush(md);
> + if (unlikely(error)) {
> + bio_endio(c, error);
> + goto next_bio;
> + }
> + if (bio_empty_barrier(c)) {
> + bio_endio(c, 0);
> + goto next_bio;
> + }
> +
> + __split_and_process_bio(md, c);
> +
> + error = dm_flush(md);
> + if (!error && md->barrier_error)
> + error = md->barrier_error;
> +
> + if (md->barrier_error != DM_ENDIO_REQUEUE)
> + bio_endio(c, error);
> + }
>
> +next_bio:
> down_write(&md->io_lock);
> }
> }
>
> --
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> dm-devel@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/dm-devel
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