On Wed, Jul 12, 2017 at 10:22:33AM +0200, Thomas Huth wrote:
> We don't want to carry along old machine types forever. If we are able to
> remove the pc machines up to 0.13 one day for example, this would allow
> us to eventually kill the code for rombar=0 (i.e. where QEMU copies ROM
> BARs directly to low memory). Everything up to pc-1.2 is also known to
> have issues with migration. So let's start with a deprecation message
> for the old machine types so that the (hopefully) few users of these old
> systems start switching over to newer machine types instead.
>
> Signed-off-by: Thomas Huth <th...@redhat.com>
> ---
> Note: Even if we mark all these old machines as deprecated, this ofcourse
> doesn't mean that we also have to remove them all at once later when we
> decide to finally really remove some. We could then also start by removing
> 0.10 and 0.11 only, for example (since there should really be no users left
> for these), or only up to 0.13 (to be able to kill rombar=0).
So I generally think the main issue is that machine types are conflating
two things. One is saying "I want to be able to migrate from/to QEMU X".
Another is saying "I want to look to guests as if I am QEMU X
but I restart gurst on the new QEMU".
First is generally a superset of the second, but only a subset of
users needs the first. And while there's a very good chance we
are actually pretty close to supporting the second even for very
old machine types, I doubt we are actually able to migrate to/from
these old QEMU versions since it is so hard to test.
So IMHO, a more significant step with a long term impact would be to
support splitting these things up.
> v3:
> - Use a more generic approach by introducing a "deprecation_msg" in the
> MachineClass instead.
>
> v2:
> - Deprecate machines up to pc-1.2
>
> hw/i386/pc_piix.c | 1 +
> include/hw/boards.h | 1 +
> vl.c | 4 ++++
> 3 files changed, 6 insertions(+)
>
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index 22dbef6..8e70308 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -707,6 +707,7 @@ static void pc_i440fx_1_2_machine_options(MachineClass *m)
> {
> pc_i440fx_1_3_machine_options(m);
> m->hw_version = "1.2.0";
> + m->deprecation_msg = "Please use a newer machine type instead.";
> SET_MACHINE_COMPAT(m, PC_COMPAT_1_2);
> }
>
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 76ce021..42a0264 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -112,6 +112,7 @@ struct MachineClass {
> char *name;
> const char *alias;
> const char *desc;
> + const char *deprecation_msg;
>
> void (*init)(MachineState *state);
> void (*reset)(void);
> diff --git a/vl.c b/vl.c
> index f7560de..0058d41 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4115,6 +4115,10 @@ int main(int argc, char **argv, char **envp)
> replay_configure(icount_opts);
>
> machine_class = select_machine();
> + if (machine_class->deprecation_msg) {
> + error_report("Machine type '%s' is deprecated. %s",
> + machine_class->name, machine_class->deprecation_msg);
> + }
>
> set_memory_options(&ram_slots, &maxram_size, machine_class);
>
> --
> 1.8.3.1
