Re: [PATCH v6 09/10] migration/yank: Keep track of registered yank instances

[Peter Xu]

On Mon, Sep 11, 2023 at 02:13:19PM -0300, Fabiano Rosas wrote:
> The core yank code is strict about balanced registering and
> unregistering of yank functions.
> 
> This creates a difficulty because the migration code registers one
> yank function per QIOChannel, but each QIOChannel can be referenced by
> more than one QEMUFile. The yank function should not be removed until
> all QEMUFiles have been closed.
> 
> Keep a reference count of how many QEMUFiles are using a QIOChannel
> that has a yank function. Only unregister the yank function when all
> QEMUFiles have been closed.
> 
> This improves the current code by removing the need for the programmer
> to know which QEMUFile is the last one to be cleaned up and fixes the
> theoretical issue of removing the yank function while another QEMUFile
> could still be using the ioc and require a yank.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/yank_functions.c | 81 ++++++++++++++++++++++++++++++++++----
>  migration/yank_functions.h |  8 ++++
>  2 files changed, 81 insertions(+), 8 deletions(-)

I worry this over-complicate things.

If you prefer the cleaness that we operate always on qemufile level, can we
just register each yank function per-qemufile?  I think qmp yank will
simply fail the 2nd call on the qemufile if the iochannel is shared with
the other one, but that's totally fine, IMHO.

What do you think?

In all cases, we should probably at least merge patch 1-8 if that can
resolve the CI issue.  I think all of them are properly reviewed.

Thanks,

-- 
Peter Xu