Re: [Beginner-Help] Help understanding the migration Code

[Amit Kumar]

Hi Alex

This was a great help, I found out VMStateDescription is defined in vmstate.h file and furthermore I was able to trace files using this struct.

I am specifically looking to find the pre-copy algorithm for live migration.

I found the following files which "may" contain it

- migration.c

- migration/ram.c

- migration/qemu-file-channel.c

- migration/colo.c

- migration/savevm.c

Can you point me in the right direction? Where exactly should I look for? Function names would be very helpful.

Thanks

On Tue, Oct 17, 2023 at 10:51 PM Alex Bennée <alex.bennee@linaro.org> wrote:

Amit Kumar <amit251098@gmail.com> writes:

> Following up on the previous email I sent. I want to understand the migration code, I have read a couple of papers on
> how it works in theory, but I am finding it hard to find a starting
> point where I can start to understand the code.

Start looking at the VMStateDescription and what follows from there.
This is the principle source of serialisation information when saving
and restoring device state.

The VMSTATE_* macros wrap up a lot of the structures.

>
> Any help would be appreciated.
>
> Thank you
>
> On Wed, Oct 11, 2023 at 9:40 AM Amit Kumar <amit251098@gmail.com> wrote:
>
>  Hi
>  I am trying to understand how migration, more specifically live-migration works in QEMU. I've tried going
>  through the source code but didn't understand much, and couldn't find documentation either. I want to work on
>  live migration and need help getting to know the code.
>  More specifically I want to understand
>  - where the pre/post copy algorithms are implemented
>  - which files/data-structures that I should look at
>  - should I need to make changes, where and how should I start?
>
>  I am new to working with such large code bases, hence need some guidance.
>
>  Thanks
>
>  Amit Kumar


--
Alex Bennée
Virtualisation Tech Lead @ Linaro