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


From: Cédric Le Goater
Subject: Re: [PATCH v5 5/8] blockdev: Add a new IF type IF_OTHER
Date: Thu, 28 Jul 2022 15:57:21 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0

On 7/28/22 15:29, Kevin Wolf wrote:
Am 28.07.2022 um 11:46 hat Peter Maydell geschrieben:
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...

How confident are we that no board will ever have two devices of this
kind?

The BMC machines have a lot of eeproms.


As long as every board has at most one, if=other is a bad user interface
in terms of descriptiveness, but still more or less workable as long as
you know what it means for the specific board you use.

But if you have more than one device, it becomes hard to predict which
device gets which backend - it depends on the initialisation order in
the code then, and I'm pretty sure that this isn't something that should
have significance in external interfaces and therefore become a stable
API.

Can't we use the drive index ?


There has been various attempts to solve this problem for the Aspeed
machines also. See below. May be we should introduce and IF_EEPROM for
the purpose.

Thanks,

C.

[PATCH v2] aspeed: qcom: add block backed FRU devices
https://www.mail-archive.com/qemu-devel@nongnu.org/msg900485.html

[PATCH] aspeed: Enable backend file for eeprom
20220728061228.152704-1-wangzhiqiang02@inspur.com/">http://patchwork.ozlabs.org/project/qemu-devel/patch/20220728061228.152704-1-wangzhiqiang02@inspur.com/



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