Re: [PATCH v6 09/18] libxl: add save/restore support for qemu-xen in stubdomain

From: Ian Jackson <ian.jackson@citrix.com>
To: Jason Andryuk <jandryuk@gmail.com>
Cc: "Anthony Perard" <anthony.perard@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
	"Wei Liu" <wl@xen.org>
Subject: Re: [PATCH v6 09/18] libxl: add save/restore support for qemu-xen in stubdomain
Date: Mon, 18 May 2020 15:24:34 +0100	[thread overview]
Message-ID: <24258.39586.245004.804616@mariner.uk.xensource.com> (raw)
In-Reply-To: <20200518011353.326287-10-jandryuk@gmail.com>

Jason Andryuk writes ("[PATCH v6 09/18] libxl: add save/restore support for qemu-xen in stubdomain"):
> From: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
...
>      if (state->saved_state) {
> -        /* This file descriptor is meant to be used by QEMU */
> -        *dm_state_fd = open(state->saved_state, O_RDONLY);
> -        flexarray_append(dm_args, "-incoming");
> -        flexarray_append(dm_args, GCSPRINTF("fd:%d",*dm_state_fd));
> +        if (is_stubdom) {
> +            /* Linux stubdomain must replace $STUBDOM_RESTORE_INCOMING_ARG
> +             * with the approriate fd:$num argument for the
> +             * STUBDOM_CONSOLE_RESTORE console 2.
> +             */
> +            flexarray_append(dm_args, "-incoming");
> +            flexarray_append(dm_args, "$STUBDOM_RESTORE_INCOMING_ARG");
> +        } else {
> +            /* This file descriptor is meant to be used by QEMU */
> +            *dm_state_fd = open(state->saved_state, O_RDONLY);
> +            flexarray_append(dm_args, "-incoming");
> +            flexarray_append(dm_args, GCSPRINTF("fd:%d",*dm_state_fd));

Hrk.  The stubdom script is expected to spot this particular value in
the dm_args array and seddery it.  OK.  This is, at leasst, sound.
I'm happy with the code and the protocol.

I think this needs a change to this doc:

  Subject: [PATCH v6 01/18] Document ioemu MiniOS stubdomain protocol

  +Toolstack to MiniOS ioemu stubdomain protocol
  +---------------------------------------------

Provided that you update the docs commit and take my ack off that,
please add my ack to this code :-).

Or you can fold the docs change into this commit, if you prefer, in
which case I'll review this patch again.

Thanks,
Ian.