Re: [Xen-devel] [XEN PATCH for-4.13 v2 9/9] libxl/xl: Overhaul passthrough setting logic

From: Wei Liu <wl@xen.org>
To: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wl@xen.org>, Andrew Cooper <Andrew.Cooper3@citrix.com>,
	Paul Durrant <pdurrant@gmail.com>,
	Jan Beulich <jbeulich@suse.com>,
	Anthony PERARD <anthony.perard@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [XEN PATCH for-4.13 v2 9/9] libxl/xl: Overhaul passthrough setting logic
Date: Fri, 11 Oct 2019 10:26:14 +0100	[thread overview]
Message-ID: <20191011092614.n4d3qygp42kbtfdu@debian> (raw)
In-Reply-To: <20191010151111.22125-10-ian.jackson@eu.citrix.com>

On Thu, Oct 10, 2019 at 04:11:11PM +0100, Ian Jackson wrote:
> LIBXL_PASSTHROUGH_UNKNOWN (aka "ENABLED" in an earlier uncommitted
> version of this code) is doing double duty.  We actually need all of
> the following to be specificable:
>   * default ("unknown"): enable PT iff we have devices to
>     pass through specified in the initial config file.
>   * "enabled" (and fail if the platform doesn't support it).
>   * "disabled" (and reject future PT hotplug).
>   * "share_pt"/"sync_pt": enable PT and set a specific PT mode.
> 
> Defaulting and error checking should be done in libxl.  So, we make
> several changes here.
> 
> We introduce "enabled".  (And we document "unknown".)
> 
> We move all of the error checking and defaulting code from xl into
> libxl.  Now, libxl__domain_config_setdefault has all of the necessary
> information to get this right.  So we can do it all there, in one
> place.
> 
> We can also arrange to have only one place each which calculates
> (i) whether passthrough needs to be enabled because pt devices were
> specified (ii) whether pt_share can be used.
> 
> xl now only has to parse the enum in the same way as it parses all
> other enums.
> 
> This change fixes a regression from earlier 4.13-pre: until recent
> changes, passthrough was only enabled by default if passthrough
> devices were specified.  We restore this behaviour.
> 
> This will hide, from the point of view of libvirt tests in osstest, a
> separate hypervisor regression which prevents migration of a domain
> with passthrough enabled but without actual PT devices.

I think Jan committed a patch to fix that, so this may need deleting.

I will let Jan and Paul confirm this.

Wei.

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