Re: [PATCH] fix Remus failover regression

[Hongyang Yang <yanghy@cn.fujitsu.com>]

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@eu.citrix.com>
>> CC: Ian Campbell <ian.campbell@citrix.com>
>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>> CC: Shriram Rajagopalan <rshriram@cs.ubc.ca>
>> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
>> ---
>>   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.