> -----Original Message----- > From: Andrew Cooper > Sent: 27 March 2019 18:20 > To: Paul Durrant <paul.durr...@citrix.com>; xen-de...@lists.xenproject.org; > qemu-bl...@nongnu.org; > qemu-devel@nongnu.org > Cc: Kevin Wolf <kw...@redhat.com>; Stefano Stabellini > <sstabell...@kernel.org>; Max Reitz > <mre...@redhat.com>; Stefan Hajnoczi <stefa...@redhat.com>; Anthony Perard > <anthony.per...@citrix.com> > Subject: Re: [Xen-devel] [PATCH v2 0/2] xen-block: fix sector size confusion > > 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.
To some extent we decided it was the *only* 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. Yes, that's how we are going to fix things. > > 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. Well the implementation is currently wrong w.r.t. the spec and these patches fix that. As long as sector-size remains at 512 then no existing frontend should break, so I guess you could argue that patch #2 should also make sure that sector-size is also 512... but that is not yet in the spec. I guess I'm ok to defer patch #2 until a revised spec. is agreed, but the ship has already sailed as far as patch #1 goes. Anthony, thoughts? Paul > > ~Andrew
