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

[Lei Li <lilei@linux.vnet.ibm.com>]

On 10/03/2013 09:34 PM, Paolo Bonzini wrote:
> 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.

Ah, I see. :)
qemu_fopen_socket_local() sounds good, thanks!

> 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
>>>
>>


-- 
Lei