block, drivers, fs: rename REQ_FLUSH to REQ_PREFLUSH

To avoid confusion between REQ_OP_FLUSH, which is handled by
request_fn drivers, and upper layers requesting the block layer
perform a flush sequence along with possibly a WRITE, this patch
renames REQ_FLUSH to REQ_PREFLUSH.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index da944ff..ca70bc7 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -2207,7 +2207,7 @@
 			       block->dev_bytenr, block->mirror_num);
 		next_block = block->next_in_same_bio;
 		block->iodone_w_error = iodone_w_error;
-		if (block->submit_bio_bh_rw & REQ_FLUSH) {
+		if (block->submit_bio_bh_rw & REQ_PREFLUSH) {
 			dev_state->last_flush_gen++;
 			if ((dev_state->state->print_mask &
 			     BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
@@ -2243,7 +2243,7 @@
 		       block->dev_bytenr, block->mirror_num);
 
 	block->iodone_w_error = iodone_w_error;
-	if (block->submit_bio_bh_rw & REQ_FLUSH) {
+	if (block->submit_bio_bh_rw & REQ_PREFLUSH) {
 		dev_state->last_flush_gen++;
 		if ((dev_state->state->print_mask &
 		     BTRFSIC_PRINT_MASK_END_IO_BIO_BH))
@@ -2884,7 +2884,7 @@
 		btrfsic_process_written_block(dev_state, dev_bytenr,
 					      &bh->b_data, 1, NULL,
 					      NULL, bh, op_flags);
-	} else if (NULL != dev_state && (op_flags & REQ_FLUSH)) {
+	} else if (NULL != dev_state && (op_flags & REQ_PREFLUSH)) {
 		if (dev_state->state->print_mask &
 		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
 			printk(KERN_INFO
@@ -2982,7 +2982,7 @@
 			kunmap(bio->bi_io_vec[i].bv_page);
 		}
 		kfree(mapped_datav);
-	} else if (NULL != dev_state && (bio->bi_rw & REQ_FLUSH)) {
+	} else if (NULL != dev_state && (bio->bi_rw & REQ_PREFLUSH)) {
 		if (dev_state->state->print_mask &
 		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
 			printk(KERN_INFO