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

[Paolo Bonzini]

Il 03/10/2013 15:29, Lei Li ha scritto:
> 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?

Yes (though I'd call it qemu_fopen_socket_local() or something like that).

On the incoming side, if non-page-flipping was enabled you will use the
normal RAM loading code, if page-flipping was enabled you will get
load_hook calls.

Paolo

>>
>> 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
>>
> 
>