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/block/blk-settings.c b/block/blk-settings.c
index 331e4ee..c903bee 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -846,6 +846,32 @@
}
EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
+/**
+ * blk_queue_write_cache - configure queue's write cache
+ * @q: the request queue for the device
+ * @wc: write back cache on or off
+ * @fua: device supports FUA writes, if true
+ *
+ * Tell the block layer about the write cache of @q.
+ */
+void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
+{
+ spin_lock_irq(q->queue_lock);
+ if (wc) {
+ queue_flag_set(QUEUE_FLAG_WC, q);
+ q->flush_flags = REQ_FLUSH;
+ } else
+ queue_flag_clear(QUEUE_FLAG_WC, q);
+ if (fua) {
+ if (wc)
+ q->flush_flags |= REQ_FUA;
+ queue_flag_set(QUEUE_FLAG_FUA, q);
+ } else
+ queue_flag_clear(QUEUE_FLAG_FUA, q);
+ spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL_GPL(blk_queue_write_cache);
+
static int __init blk_settings_init(void)
{
blk_max_low_pfn = max_low_pfn - 1;