Re: [Qemu-devel] [PATCH 2/2] atapi migration: Throw recoverable error to avoid recovery

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> 
> 
> On 09/12/2014 19:15, Dr. David Alan Gilbert (git) wrote:
> > (With the previous atapi_dma flag recovery)
> > If migration happens between the ATAPI command being written and the
> > bmdma being started, the DMA is dropped.  Eventually the guest times
> > out and recovers, but that can take many seconds.
> > (This is rare, on a pingpong reading the CD continuously I hit
> > this about ~1/30-1/50 migrates)
> > 
> > I don't think we've got enough state to be able to recover safely
> > at this point, so I throw a 'medium error, no seek complete'
> > that I'm assuming guests will try and recover from an apparently
> > dirty CD.
> 

> Also, what is the ATAPI command that is being run?

The command in my test case is:
28 00 00 06 df b8 00 00 40 00 00 00
so just a standard READ (10); I guess it's possible that other OSs/operations
maybe doing different READ variants.

> What is the part of the state that is not being migrated?

I can't see lba, io_buffer_index, io_buffer_size or cd_sector_size being passed
to a VMSTATE_ macro; and having noticed that those are missing I didn't dig much
deeper.
(I'll admit to not really understanding the interaction between the core.c, atapi.c
and pci.c dma code properly to know if it can be reconstructed).

Dave

> Paolo
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK