Re: [Xen-devel] [PATCH] fix Remus failover regression

[Hongyang Yang <yanghy@xxxxxxxxxxxxxx>]

On 07/28/2014 12:05 PM, Wen Congyang wrote:
> At 07/28/2014 11:35 AM, Yang Hongyang Write:
> > commit: c2ba706c
> > tools/libxc: goto correct label on error paths by Andrew broke
> > Remus in Xen 4.4 or earlier versions that has this commit backported.
> >
> > With Remus, this jump essentially discards the last incomplete
> > checkpoint received by the backup.
> > This is required for Remus to work and this does not break live
> > migration.
> >
> > CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > CC: Shriram Rajagopalan <rshriram@xxxxxxxxx>
> > Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> > ---
> >   tools/libxc/xc_domain_restore.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/libxc/xc_domain_restore.c b/tools/libxc/xc_domain_restore.c
> > index e73e0a2..5d2fbd6 100644
> > --- a/tools/libxc/xc_domain_restore.c
> > +++ b/tools/libxc/xc_domain_restore.c
> > @@ -1783,14 +1783,14 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
> > uint32_t dom,
> >
> >       if ( pagebuf_get(xch, ctx, &pagebuf, io_fd, dom) ) {
> >           PERROR("error when buffering batch, finishing");
> > -        goto out;
> > +        goto finish;
> >       }
> >       memset(&tmptail, 0, sizeof(tmptail));
> >       tmptail.ishvm = hvm;
> >       if ( buffer_tail(xch, ctx, &tmptail, io_fd, max_vcpu_id, vcpumap,
> >                        ext_vcpucontext, vcpuextstate_size) < 0 ) {
> >           ERROR ("error buffering image tail, finishing");
> > -        goto out;
> > +        goto finish;
> >       }
> >       tailbuf_free(&tailbuf);
> >       memcpy(&tailbuf, &tmptail, sizeof(tailbuf));
> The mail is here:
> http://lists.xenproject.org/archives/html/xen-devel/2014-01/msg02299.html
>
> > Both of these errors have been discovered by xc_domain_restore() returning
> > success after suffering a fatal error during migration, leading to the
> > toolstack believing that the VM migrated successfully.
> These codes are only for Remus. So, why these codes are executed by migration?
I was confused also, without Remus, these two error path will not be hitted I
think, without Remus, migration will ended at:
1776     if ( ctx->last_checkpoint )
1777     {
1778         // DPRINTF("Last checkpoint, finishing\n");
1779         goto finish;
1780     }

> Thanks
> Wen Congyang
>
>
> .
--
Thanks,
Yang.

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