linux-kernel - Re: [RFC/PATCHSET 0/3] virtio: Implement virtio pstore device (v3)

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Date:   Wed, 24 Aug 2016 00:10:22 -0700
From:   Joel <agnel.joel@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        qemu-devel <qemu-devel@...gnu.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC/PATCHSET 0/3] virtio: Implement virtio pstore device (v3)

Hi Namhyung,

> On Aug 23, 2016, at 8:20 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> 
> Hi Joel,
> 
> On Tue, Aug 23, 2016 at 7:25 PM, Joel Fernandes <agnel.joel@...il.com> wrote:
>> From: Namhyung Kim <namhyung@...nel.org>
> 
>> 
>> Any thoughts on what you think about it? In your approach though, you
>> wouldn't need a backing mem-path file which is the size of the guest
>> RAM (which could be as big as the mem-path file). I wonder if the
>> mem-path file can be created sparse, and/or Qemu has support to
>> configure a certain part of guest RAM as file-backed memory and the
>> rest of it from Anonymous memory (not backed by mem-path) so that
>> the size of the mem-path file can be kept at a minimum.
> 
> The pstore (ramoops) requires the region of the memory is preserved
> across reboot.  Is it possible when -mem-path is used?  I think it’s

I believe the stock qemu won’t persist memory on its own without a reboot.
I found atleast one post where someone was trying to make mem-path
persist across a reboot and claimed to succeed:
https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg03476.html

> 
> Also my approach can handle streams of data bigger than the pstore
> buffer size.  Although we can extract the contents of mem-path file
> periodically, it might be hard for externel process to know the right
> time to extract and there's a possibility of information loss IMHO.
> 

I agree, your approach is better for an emulated environment.

Thanks,
Joel

> Thanks,
> Namhyung