1 files changed, 262 insertions, 0 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
new file mode 100644
index 0000000..54b123d
--- /dev/null
+++ b/block/blk-flush.c
@@ -0,0 +1,262 @@
+/*
+ * Functions to sequence FLUSH and FUA writes.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/gfp.h>
+
+#include "blk.h"
+
+/* FLUSH/FUA sequences */
+enum {
+	QUEUE_FSEQ_STARTED	= (1 << 0), /* flushing in progress */
+	QUEUE_FSEQ_PREFLUSH	= (1 << 1), /* pre-flushing in progress */
+	QUEUE_FSEQ_DATA		= (1 << 2), /* data write in progress */
+	QUEUE_FSEQ_POSTFLUSH	= (1 << 3), /* post-flushing in progress */
+	QUEUE_FSEQ_DONE		= (1 << 4),
+};
+
+static struct request *queue_next_fseq(struct request_queue *q);
+
+unsigned blk_flush_cur_seq(struct request_queue *q)
+{
+	if (!q->flush_seq)
+		return 0;
+	return 1 << ffz(q->flush_seq);
+}
+
+static struct request *blk_flush_complete_seq(struct request_queue *q,
+					      unsigned seq, int error)
+{
+	struct request *next_rq = NULL;
+
+	if (error && !q->flush_err)
+		q->flush_err = error;
+
+	BUG_ON(q->flush_seq & seq);
+	q->flush_seq |= seq;
+
+	if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
+		/* not complete yet, queue the next flush sequence */
+		next_rq = queue_next_fseq(q);
+	} else {
+		/* complete this flush request */
+		__blk_end_request_all(q->orig_flush_rq, q->flush_err);
+		q->orig_flush_rq = NULL;
+		q->flush_seq = 0;
+
+		/* dispatch the next flush if there's one */
+		if (!list_empty(&q->pending_flushes)) {
+			next_rq = list_entry_rq(q->pending_flushes.next);
+			list_move(&next_rq->queuelist, &q->queue_head);
+		}
+	}
+	return next_rq;
+}
+
+static void blk_flush_complete_seq_end_io(struct request_queue *q,
+					  unsigned seq, int error)
+{
+	bool was_empty = elv_queue_empty(q);
+	struct request *next_rq;
+
+	next_rq = blk_flush_complete_seq(q, seq, error);
+
+	/*
+	 * Moving a request silently to empty queue_head may stall the
+	 * queue.  Kick the queue in those cases.
+	 */
+	if (was_empty && next_rq)
+		__blk_run_queue(q);
+}
+
+static void pre_flush_end_io(struct request *rq, int error)
+{
+	elv_completed_request(rq->q, rq);
+	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
+}
+
+static void flush_data_end_io(struct request *rq, int error)
+{
+	elv_completed_request(rq->q, rq);
+	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
+}
+
+static void post_flush_end_io(struct request *rq, int error)
+{
+	elv_completed_request(rq->q, rq);
+	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
+}
+
+static void init_flush_request(struct request *rq, struct gendisk *disk)
+{
+	rq->cmd_type = REQ_TYPE_FS;
+	rq->cmd_flags = WRITE_FLUSH;
+	rq->rq_disk = disk;
+}
+
+static struct request *queue_next_fseq(struct request_queue *q)
+{
+	struct request *orig_rq = q->orig_flush_rq;
+	struct request *rq = &q->flush_rq;
+
+	blk_rq_init(q, rq);
+
+	switch (blk_flush_cur_seq(q)) {
+	case QUEUE_FSEQ_PREFLUSH:
+		init_flush_request(rq, orig_rq->rq_disk);
+		rq->end_io = pre_flush_end_io;
+		break;
+	case QUEUE_FSEQ_DATA:
+		init_request_from_bio(rq, orig_rq->bio);
+		/*
+		 * orig_rq->rq_disk may be different from
+		 * bio->bi_bdev->bd_disk if orig_rq got here through
+		 * remapping drivers.  Make sure rq->rq_disk points
+		 * to the same one as orig_rq.
+		 */
+		rq->rq_disk = orig_rq->rq_disk;
+		rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
+		rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
+		rq->end_io = flush_data_end_io;
+		break;
+	case QUEUE_FSEQ_POSTFLUSH:
+		init_flush_request(rq, orig_rq->rq_disk);
+		rq->end_io = post_flush_end_io;
+		break;
+	default:
+		BUG();
+	}
+
+	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
+	return rq;
+}
+
+struct request *blk_do_flush(struct request_queue *q, struct request *rq)
+{
+	unsigned int fflags = q->flush_flags; /* may change, cache it */
+	bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
+	bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
+	bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
+	unsigned skip = 0;
+
+	/*
+	 * Special case.  If there's data but flush is not necessary,
+	 * the request can be issued directly.
+	 *
+	 * Flush w/o data should be able to be issued directly too but
+	 * currently some drivers assume that rq->bio contains
+	 * non-zero data if it isn't NULL and empty FLUSH requests
+	 * getting here usually have bio's without data.
+	 */
+	if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
+		rq->cmd_flags &= ~REQ_FLUSH;
+		if (!has_fua)
+			rq->cmd_flags &= ~REQ_FUA;
+		return rq;
+	}
+
+	/*
+	 * Sequenced flushes can't be processed in parallel.  If
+	 * another one is already in progress, queue for later
+	 * processing.
+	 */
+	if (q->flush_seq) {
+		list_move_tail(&rq->queuelist, &q->pending_flushes);
+		return NULL;
+	}
+
+	/*
+	 * Start a new flush sequence
+	 */
+	q->flush_err = 0;
+	q->flush_seq |= QUEUE_FSEQ_STARTED;
+
+	/* adjust FLUSH/FUA of the original request and stash it away */
+	rq->cmd_flags &= ~REQ_FLUSH;
+	if (!has_fua)
+		rq->cmd_flags &= ~REQ_FUA;
+	blk_dequeue_request(rq);
+	q->orig_flush_rq = rq;
+
+	/* skip unneded sequences and return the first one */
+	if (!do_preflush)
+		skip |= QUEUE_FSEQ_PREFLUSH;
+	if (!blk_rq_sectors(rq))
+		skip |= QUEUE_FSEQ_DATA;
+	if (!do_postflush)
+		skip |= QUEUE_FSEQ_POSTFLUSH;
+	return blk_flush_complete_seq(q, skip, 0);
+}
+
+static void bio_end_flush(struct bio *bio, int err)
+{
+	if (err)
+		clear_bit(BIO_UPTODATE, &bio->bi_flags);
+	if (bio->bi_private)
+		complete(bio->bi_private);
+	bio_put(bio);
+}
+
+/**
+ * blkdev_issue_flush - queue a flush
+ * @bdev:	blockdev to issue flush for
+ * @gfp_mask:	memory allocation flags (for bio_alloc)
+ * @error_sector:	error sector
+ *
+ * Description:
+ *    Issue a flush for the block device in question. Caller can supply
+ *    room for storing the error offset in case of a flush error, if they
+ *    wish to. If WAIT flag is not passed then caller may check only what
+ *    request was pushed in some internal queue for later handling.
+ */
+int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
+		sector_t *error_sector)
+{
+	DECLARE_COMPLETION_ONSTACK(wait);
+	struct request_queue *q;
+	struct bio *bio;
+	int ret = 0;
+
+	if (bdev->bd_disk == NULL)
+		return -ENXIO;
+
+	q = bdev_get_queue(bdev);
+	if (!q)
+		return -ENXIO;
+
+	/*
+	 * some block devices may not have their queue correctly set up here
+	 * (e.g. loop device without a backing file) and so issuing a flush
+	 * here will panic. Ensure there is a request function before issuing
+	 * the flush.
+	 */
+	if (!q->make_request_fn)
+		return -ENXIO;
+
+	bio = bio_alloc(gfp_mask, 0);
+	bio->bi_end_io = bio_end_flush;
+	bio->bi_bdev = bdev;
+	bio->bi_private = &wait;
+
+	bio_get(bio);
+	submit_bio(WRITE_FLUSH, bio);
+	wait_for_completion(&wait);
+
+	/*
+	 * The driver must store the error location in ->bi_sector, if
+	 * it supports it. For non-stacked drivers, this should be
+	 * copied from blk_rq_pos(rq).
+	 */
+	if (error_sector)
+               *error_sector = bio->bi_sector;
+
+	if (!bio_flagged(bio, BIO_UPTODATE))
+		ret = -EIO;
+
+	bio_put(bio);
+	return ret;
+}
+EXPORT_SYMBOL(blkdev_issue_flush);