Re: [PATCH V2] migration: file URI

[Steven Sistare <steven.sistare@oracle.com>]

On 6/12/2023 2:44 PM, Peter Xu wrote:
> Hi, Steve,
> 
> On Wed, Jun 07, 2023 at 11:38:59AM -0700, Steve Sistare wrote:
>> Extend the migration URI to support file:<filename>.  This can be used for
>> any migration scenario that does not require a reverse path.  It can be used
>> as an alternative to 'exec:cat > file' in minimized containers that do not
>> contain /bin/sh, and it is easier to use than the fd:<fdname> URI.  It can
>> be used in HMP commands, and as a qemu command-line parameter.
> 
> I have similar question on the fixed-ram work,

Sorry, what is the "fixed-ram work"?

> on whether we should assume
> the vm stopped before doing so.  Again, it leaves us space for
> optimizations on top without breaking anyone.

I do not assume the vm is stopped.  The migration code will stop the vm
in migration_iteration_finish.

> The other thing is considering a very busy guest, migration may not even
> converge for "file:" URI (the same to other URIs) but I think that doesn't
> make much sense to not converge for a "file:" URI.  The user might be very
> confused too.

The file URI is mainly intended for the case where guest ram is backed by shared memory 
and preserved in place, in which case writes are not tracked and convergence is not an
issue.  If not shared memory, the user should be advised to stop the machine first.
I should document these notes in qemu-options and/or migration.json.

- Steve