Re: [PATCH v5 5/8] blockdev: Add a new IF type IF_OTHER

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Thu, Aug 04, 2022 at 04:56:15PM +0200, Markus Armbruster wrote:
>> Daniel P. Berrangé <berrange@redhat.com> writes:
>> 
>> > On Thu, Jul 28, 2022 at 10:46:35AM +0100, Peter Maydell wrote:
>> >> On Wed, 27 Jul 2022 at 20:03, Kevin Wolf <kwolf@redhat.com> wrote:
>> >> >
>> >> > Am 18.07.2022 um 11:49 hat Markus Armbruster geschrieben:
>> >> > > An OTP device isn't really a parallel flash, and neither are eFuses.
>> >> > > More fast-and-lose use of IF_PFLASH may exist in the tree, and maybe 
>> >> > > of
>> >> > > other interface types, too.
>> >> > >
>> >> > > This patch introduces IF_OTHER.  The patch after next uses it for an
>> >> > > EEPROM device.
>> >> > >
>> >> > > Do we want IF_OTHER?
>> >> >
>> >> > What would the semantics even be? Any block device that doesn't pick up
>> >> > a different category may pick up IF_OTHER backends?
>> >> >
>> >> > It certainly feels like a strange interface to ask for "other" disk and
>> >> > then getting as surprise what this other thing might be. It's
>> >> > essentially the same as having an explicit '-device other', and I
>> >> > suppose most people would find that strange.
>> >> >
>> >> > > If no, I guess we get to abuse IF_PFLASH some more.
>> >> > >
>> >> > > If yes, I guess we should use IF_PFLASH only for actual parallel flash
>> >> > > memory going forward.  Cleaning up existing abuse of IF_PFLASH may not
>> >> > > be worth the trouble, though.
>> >> > >
>> >> > > Thoughts?
>> >> >
>> >> > If the existing types aren't good enough (I don't have an opinion on
>> >> > whether IF_PFLASH is a good match), let's add a new one. But a specific
>> >> > new one, not just "other".
>> >> 
>> >> I think the common thread is "this isn't what anybody actually thinks
>> >> of as being a 'disk', but we would like to back it with a block device
>> >> anyway". That can cover a fair range of possibilities...
>> >
>> > Given that, do we even want/have to use -drive for this ?    We can use
>> > -blockdev for the backend and reference that from any -device we want
>> > to create, and leave -drive out of the picture entirely
>> 
>> -drive is our only means to configure onboard devices.
>> 
>> We've talked about better means a few times, but no conclusions.  I can
>> dig up pointers, if you're interested.
>
> For onboard pflash with x86, we've just got properties against the
> machine that we can point to a blockdev.

True, but the vast majority of onboard block devices doesn't come with
such properties.  Please see

Subject: On configuring onboard block devices with -blockdev (was: [PATCH v4 
6/7] hw/nvram: Update at24c EEPROM init function in NPCM7xx boards)
Date: Mon, 15 Nov 2021 16:28:33 +0100
Message-ID: <875ystigke.fsf_-_@dusky.pond.sub.org>
https://lists.gnu.org/archive/html/qemu-devel/2021-11/msg03173.html