Re: [Xen-devel] [PATCH] blkif.h: document scsi/0x12/0x<NN> node

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, 23 Mar 2016, Paul Durrant wrote:
> > -----Original Message-----
> [snip]
> > > > >
> > > > > For this part, there is ioctl() interface for all block device.
> > > > > Looking at virtio-blk in KVM world, it can accept almost all SCSI
> > commands
> > > > also in ioctl() even they already have virtio-scsi.
> > > > > But that's another story.
> > > > >
> > > >
> > > > So this means that you would then need to add a bunch of new request
> > > > types
> > > > to the PV block protocol in order to make use of this new exported
> > > > information?
> > > >
> > >
> > > No, why do you think that? The info is in xenstore so why does the blkif
> > protocol need to be involved at all?
> > 
> > Sorry, I'm just trying to figure out how is this going to be used.
> > 
> > Isn't this information going to have some impact on how the user uses
> > the block device? If not, why are we exporting it then?
> > 
> 
> I assume that the user will want to get this information from blkfront via 
> ioctl (as Bob suggests), but blkfront can just pull it straight from 
> xenstore. No need for any communication with blkback.

Yes, I understand this. What I want to know is what impact is this 
information going to have on how the user uses the PV block device.

Is the information found in this magic page going to be used to try to 
send requests of specfic size in order to take advantge of some hw 
features?

And then my other question is, in order to take advantadge of this 
information, will we need to add new PV block request types that 
encapsulate SCSI commands?

TBH, ATM I don't see why this is useful at all.

Roger.

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