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

From: Jens Axboe
Date: Wed Mar 30 2016 - 11:48:13 EST

On 03/30/2016 09:42 AM, Christoph Hellwig wrote:
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 :))

That's fine, I don't mind making that change, just didn't do it for this version. I prefer if we change the cache flagging to be the primary way to signal it, it's more intuitive than REQ_FLUSH.

It'll be in the next version.

Jens Axboe