Re: [PATCH 5/9] block: add ability to flag write back caching on a device

[Christoph Hellwig]

On Wed, Mar 30, 2016 at 09:07:53AM -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.

As per previous discussion:  I don't really care about the way how we
tell the block layer we have a writeback cache, but a NAK to having
each driver call two interfaces to convey the same information.

Please just look at q->flush_flag & REQ_FLUSH for now, and then
improvem the interface if you don't like it (I don't particularly like
it, but not to the point that I'm motivated enough to fix it :))