Re: [Qemu-block] [Xen-devel] [PATCH v2 0/2] xen-block: fix sector size confusion

[Andrew Cooper]

On 27/03/2019 17:32, Paul Durrant wrote:
> The Xen blkif protocol is confusing but discussion with the maintainer
> has clarified that sector based quantities in requests and the 'sectors'
> value advertized in xenstore should always be in terms of 512-byte
> units and not the advertised logical 'sector-size' value.
>
> This series fixes xen-block to adhere to the spec.

I thought we agreed that hardcoding things to 512 bytes was the wrong
thing to do.

I was expecting something like:

1) Clarify the spec with the intended meaning, (which is what some
implementations actually use already) and wont cripple 4k datapaths.
2) Introduce a compatibility key for "I don't rely on sector-size being
512", which fixed implementations should advertise.
3) Specify that because of bugs in the spec which got out into the wild,
drivers which don't find the key being advertised by the other end
should emulate sector-size=512 for compatibility with broken
implementations.

Whatever the eventual way out, the first thing which needs to happen is
an update to the spec, before actions are taken to alter existing
implementations.

~Andrew