Re: [Qemu-devel] [PATCH] migration: fix incorrect enable return path

[Laurent Vivier <lvivier@redhat.com>]

On 15/06/2017 18:54, Laurent Vivier wrote:
> On 14/06/2017 09:55, Peter Xu wrote:
>> 0425dc9 is actually v1 of that patch, but it was accidentally
>> merged (while there was a v2). That will cause problem when we try to
>> migrate to some old QEMUs when return path is not really there. Let's
>> fix it, then squashing this patch with 0425dc9 will be exactly patch
>> content of v2.
>>
>> Fixes: 0425dc9 ("migration: isolate return path on src")
>> Signed-off-by: Peter Xu <peterx@redhat.com>
>> ---
>>  migration/migration.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/migration/migration.c b/migration/migration.c
>> index 8ef6d6c..f9053b0 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -1814,7 +1814,11 @@ static void *migration_thread(void *opaque)
>>  
>>      qemu_savevm_state_header(s->to_dst_file);
>>  
>> -    if (s->to_dst_file) {
>> +    /*
>> +     * If we opened the return path, we need to make sure dst has it
>> +     * opened as well.
>> +     */
>> +    if (s->rp_state.from_dst_file) {
>>          /* Now tell the dest that it should open its end so it can reply */
>>          qemu_savevm_send_open_return_path(s->to_dst_file);
>>  
>>
> 
> Tested-by: Laurent Vivier <lvivier@redhat.com>
> 
> This also fixes migration of pseries guest, using the same
> binary/machine type on both side, the error was:
> 
> qemu-system-ppc64: Failed to load spapr_iommu:mig_table
> qemu-system-ppc64: error while loading state for instance 0x80000001 of
> device 'spapr_iommu'
> qemu-system-ppc64: load of migration failed: Input/output error

The error is an IEO because the file descriptor is closed on source. It
seems the source closes the stream too early without this patch.
For test purpose, I have disabled the qemu_fclose() on the source, and
the error disappears from the destination.

Laurent