Re: [Xen-devel] [PATCH v3 4/4] libxl: add support for vscsi

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-03-26 at 13:55 +0100, Olaf Hering wrote:
> On Fri, Mar 13, Ian Campbell wrote:
> 
> > > > > > On Fri, 2015-03-06 at 10:45 +0100, Olaf Hering wrote:
> > > > > > > +    ("feature_host",     bool),
> > > > > > What is this feature thing? What does !host imply?
> > > > > This enables raw SCSI command passthrough in xenlinux. If the flag is
> > > > > off then each command is checked. The check allows many commands to
> > > > > passthrough, one command needs emulation and unhandled commands are
> > > > > rejected. The flag is a noop in pvops because it doesnt look at such
> > > > > flag. I was told its not required, dont know the details.
> > > > Sounds like it at the very least needs a better name.
> > > Ok, will rename it to feature_noemul or feature_xenlinux_raw_scsicmd or
> > > whatever.
> > Neither of those appear to be a good description of what you say quoted
> > above.
> 
> Ian, after some thought its not clear to me why the name "feature_host"
> should be changed. The config option is "feature-host", the backend
> expects a property named "feature-host". So it seems natural to also
> name the variable that way. In the end it just passes a boolean from the
> config to xenstore, nothing else is done with it.

Regardless of the current internal details feature_host gives me no clue
at all what the flag does, and this is a public facing API.

If not a better name then some docs (or a pointer to them) would help.

> > Also, should this be a defbool or not?
> 
> This is a good idea. I remmeber xend had code to make sure that all
> devices within a vhost had the same value for "feature-host". I think
> the intention was that whole physical hosts are passed to a domU. A
> defbool makes it easier to preserve the initial value based on the first
> config item.

In which case it sounds to me like this flag should be at a per-vhost
level and not at a per device level.

Ian.


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