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authorJames Bottomley <James.Bottomley@HansenPartnership.com>2008-01-10 11:30:36 -0600
committerJens Axboe <jens.axboe@oracle.com>2008-01-28 10:54:11 +0100
commitfa0ccd837e3dddb44c7db2f128a8bb7e4eabc21a (patch)
treeade071502f3e7cba423295890d828f0f301ad731 /block/elevator.c
parent5d84070ee0a433620c57e85dac7f82faaec5fbb3 (diff)
block: implement drain buffers
These DMA drain buffer implementations in drivers are pretty horrible to do in terms of manipulating the scatterlist. Plus they're being done at least in drivers/ide and drivers/ata, so we now have code duplication. The one use case for this, as I understand it is AHCI controllers doing PIO mode to mmc devices but translating this to DMA at the controller level. So, what about adding a callback to the block layer that permits the adding of the drain buffer for the problem devices. The idea is that you'd do this in slave_configure after you find one of these devices. The beauty of doing it in the block layer is that it quietly adds the drain buffer to the end of the sg list, so it automatically gets mapped (and unmapped) without anything unusual having to be done to the scatterlist in driver/scsi or drivers/ata and without any alteration to the transfer length. Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block/elevator.c')
-rw-r--r--block/elevator.c26
1 files changed, 25 insertions, 1 deletions
diff --git a/block/elevator.c b/block/elevator.c
index f9736fbdab0..8cd5775acd7 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -741,7 +741,21 @@ struct request *elv_next_request(struct request_queue *q)
q->boundary_rq = NULL;
}
- if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
+ if (rq->cmd_flags & REQ_DONTPREP)
+ break;
+
+ if (q->dma_drain_size && rq->data_len) {
+ /*
+ * make sure space for the drain appears we
+ * know we can do this because max_hw_segments
+ * has been adjusted to be one fewer than the
+ * device can handle
+ */
+ rq->nr_phys_segments++;
+ rq->nr_hw_segments++;
+ }
+
+ if (!q->prep_rq_fn)
break;
ret = q->prep_rq_fn(q, rq);
@@ -754,6 +768,16 @@ struct request *elv_next_request(struct request_queue *q)
* avoid resource deadlock. REQ_STARTED will
* prevent other fs requests from passing this one.
*/
+ if (q->dma_drain_size && rq->data_len &&
+ !(rq->cmd_flags & REQ_DONTPREP)) {
+ /*
+ * remove the space for the drain we added
+ * so that we don't add it again
+ */
+ --rq->nr_phys_segments;
+ --rq->nr_hw_segments;
+ }
+
rq = NULL;
break;
} else if (ret == BLKPREP_KILL) {