Re: [Qemu-devel] [PATCH 0/8 RFC] migration: Introduce side channel for RAM

[Lei Li]

On 10/03/2013 06:34 PM, Paolo Bonzini wrote:
> Il 03/10/2013 12:28, Lei Li ha scritto:
> > The load_hook callback is only be called if the RAM_SAVE_FLAG_HOOK is
> > received.
> > To check this flags, it means there would be a check action first in
> > unix_accept_incoming_migration(), like:
> >
> > f = qemu_fopen_pipe(c, "rb");
> > flags = qemu_get_be64(f);
> > if (flags == RAM_SAVE_FLAG_HOOK) {
> >      load_hook();
> >      ...
> > }
> >
> > Otherwise, the incoming side has no idea whether the special 8-bytes record
> > (RAM_SAVE_FLAG_HOOK) is sent.
> No, ram_load is taking care of checking for RAM_SAVE_FLAG_HOOK.  If
> before_iterate writes the 8 bytes (followed by passing the fd for the
> pipe's read-side via SCM_RIGHTS), ram_load will call load_hook before it
> loads any page and load_hook will fetch the fd.

If let ram_load take care of checking for RAM_SAVE_FLAG_HOOK, then in
unix_accept_incoming_migration(), how to decide which QEMUFile should
be opened? Since there would be two types of QEMUFile, one is the original
QEMUFile opened by qemu_fopen_socket() for normal Unix migration, the
other is opened by qemu_fopen_pipe() for unix-page-flipping migration.

Or, were you suggesting replace this qemu_fopen_socket() with the
qemu_fopen_pipe(), which also contain the copy of the QEMUFile code for
Unix sockets?

> Subsequent calls to load_hook will match data written by the sender's
> save_page hook (so they contain a RAM address, with the 4k page data
> sent on the pipe).
>
> Paolo


--
Lei