block: add ability to flag write back caching on a device
Add an internal helper and flag for setting whether a queue has
write back caching, or write through (or none). Add a sysfs file
to show this as well, and make it changeable from user space.
This will replace the (awkward) blk_queue_flush() interface that
drivers currently use to inform the block layer of write cache state
and capabilities.
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index bbaa767..ba72687 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -491,6 +491,8 @@
#define QUEUE_FLAG_INIT_DONE 20 /* queue is initialized */
#define QUEUE_FLAG_NO_SG_MERGE 21 /* don't attempt to merge SG segments*/
#define QUEUE_FLAG_POLL 22 /* IO polling enabled if set */
+#define QUEUE_FLAG_WC 23 /* Write back caching */
+#define QUEUE_FLAG_FUA 24 /* device supports FUA writes */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
@@ -1009,6 +1011,7 @@
extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
extern void blk_queue_flush(struct request_queue *q, unsigned int flush);
extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
+extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);