RE: [PATCH 0/6] block: add support for REQ_OP_VERIFY

Clay Mayers
2022-12-03T15:39:58Z

> From: Keith Busch
> On Fri, Dec 02, 2022 at 08:16:30AM +0100, Hannes Reinecke wrote:
> > On 12/1/22 20:39, Matthew Wilcox wrote:
> > > On Thu, Dec 01, 2022 at 06:12:46PM +0000, Chaitanya Kulkarni wrote:
> > > > So nobody can get away with a lie.
> > >
> > > And yet devices do exist which lie. I'm not surprised that vendors
> > > vehemently claim that they don't, or "nobody would get away with it".
> > > But, of course, they do. And there's no way for us to find out if
> > > they're lying!

My guess, if true, is it's rationalized with the device is already
doing patrols in the background - why verify when it's already
been recently patrolled?

> > >
> > But we'll never be able to figure that out unless we try.
> >
> > Once we've tried we will have proof either way.
>
> As long as the protocols don't provide proof-of-work, trying this
> doesn't really prove anything with respect to this concern.

I'm out of my depth here, but isn't VERIFY tightly related to PI and
at the heart of detecting SAN bit-rot? The proof of work can be via
end-to-end data protection. VERIFY has to actually read to detect bad
host generated PI guard/tags. I'm assuming the PI checks can be
disabled for WRITE and enabled for VERIFY as the test.