Re: [PATCH 3/6] block: add ability to flag write back caching on a device

[Christoph Hellwig]

On Tue, Mar 22, 2016 at 11:55:17AM -0600, Jens Axboe wrote:
> 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.

We do this by passing the REQ_FLUSH flag to blk_queue_flush today.
While that's not a great interface, adding a second one doesn't make it
any better :)