linux-kernel - Re: [PATCH 1/3] virtio: Basic implementation of virtio pstore driver

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Date:   Tue, 15 Nov 2016 23:36:29 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        virtio-dev@...ts.oasis-open.org, Tony Luck <tony.luck@...el.com>,
        Kees Cook <keescook@...omium.org>, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Anton Vorontsov <anton@...msg.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>, qemu-devel@...gnu.org,
        Minchan Kim <minchan@...nel.org>,
        Anthony Liguori <aliguori@...zon.com>,
        Colin Cross <ccross@...roid.com>,
        virtualization@...ts.linux-foundation.org,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/3] virtio: Basic implementation of virtio pstore driver

Hi,

On Tue, Nov 15, 2016 at 10:57:29AM +0100, Paolo Bonzini wrote:
> 
> 
> On 15/11/2016 06:06, Michael S. Tsirkin wrote:
> > On Tue, Nov 15, 2016 at 01:50:21PM +0900, Namhyung Kim wrote:
> >> Hi Michael,
> >>
> >> On Thu, Nov 10, 2016 at 06:39:55PM +0200, Michael S. Tsirkin wrote:
> >>> On Sat, Aug 20, 2016 at 05:07:42PM +0900, Namhyung Kim wrote:
> >>>> The virtio pstore driver provides interface to the pstore subsystem so
> >>>> that the guest kernel's log/dump message can be saved on the host
> >>>> machine.  Users can access the log file directly on the host, or on the
> >>>> guest at the next boot using pstore filesystem.  It currently deals with
> >>>> kernel log (printk) buffer only, but we can extend it to have other
> >>>> information (like ftrace dump) later.
> >>>>
> >>>> It supports legacy PCI device using single order-2 page buffer.
> >>>
> >>> Do you mean a legacy virtio device? I don't see why
> >>> you would want to support pre-1.0 mode.
> >>> If you drop that, you can drop all cpu_to_virtio things
> >>> and just use __le accessors.
> >>
> >> I was thinking about the kvmtools which lacks 1.0 support AFAIK.
> > 
> > Unless kvmtools wants to be left behind it has to go 1.0.
> 
> And it also has to go ACPI.  Is there any reason, apart from kvmtool, to
> make a completely new virtio device, with no support in existing guests,
> rather than implement ACPI ERST?

Well, I know nothing about ACPI.  It looks like a huge spec and I
don't want to dig into it just for this.

What I want is to speed up dumping guest kernel message (especially
for ftrace dump).

Thanks,
Namhyung