Re: ublk vs write cache and FUA

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jul 21, 2022 at 11:27:28PM +0800, Ming Lei wrote:
> On Thu, Jul 21, 2022 at 05:14:58PM +0200, Christoph Hellwig wrote:
> > Hi Ming,
> > 
> > ublk implements REQ_OP_FLUSH and REQ_FUA, but will never see those as
> > it never calls blk_queue_write_cache.  Can we drop the code?  Or should
> > there be a flag to enable write cache and fua support when setting up
> > a device?
> 
> There should have been flags defined in ublksrv_ctrl_dev_info for describe
> wc/fua info, since ublk_drv doesn't handle any device specific logic.
> 
> So please keep REQ_OP_FLUSH and REQ_FUA which two should be useful, and I
> will add flags and related code to use them.

Actually we can add two commands for set/get device parameter, then at least
generic block device parameters(wc, fua, discard, zoned, rototional, ...)
can be configurable, so all kinds of block device can be simulated
with userspace ublk.

Thanks,
Ming