[Drbd-dev] [RESEND RFC PATCH 00/32] separate operations from flags in the bio/request structs

[Christoph Hellwig]

On Wed, Nov 04, 2015 at 04:07:57PM -0600, mchristi at redhat.com wrote:
> Known issues:
> - REQ_FLUSH is still a flag, but should probably be a operation.
>  For lower level drivers like SCSI where we only get a flush, it makes
> more sense to be a operation. However, upper layers like filesystems
> can send down flushes with writes, so it is more of a flag for them.
> I am still working on this.

Actually it should be both.  REQ_OP_FLUSH for a real flush operation,
and a REQ_PREFLUSH bio flag that the request layer will sequence into
an actual write an a flush operation.