Re: [Qemu-devel] [PATCH 3/3 resend v2] arch_init: right return for ram_save_iterate

[Lei Li <lilei@linux.vnet.ibm.com>]

On 09/11/2013 07:27 PM, Paolo Bonzini wrote:
> Il 11/09/2013 13:06, Juan Quintela ha scritto:
>>>> And I think that the right solution is make qemu_get_rate_limit() to
>>>> return -1 in case of error (or the error, I don't care).
>>> You might do both things, it would avoid the useless g_usleep you
>>> pointed out below.  But Lei's patch is good, because an error could
>>> happen exactly during the qemu_put_be64 that writes RAM_SAVE_FLAG_EOS.
>> Caller checks also.  This is the reason I wanted qemu_file_* callers to
>> return an error.  It has some advantages and some disadvantages.  We
>> don't agree on which ones are bigger O:-)
> I think the disadvantages are bigger.  It litters the code with error
> handling, hides where things actually happen, and doesn't even simplify
> QEMUFile itself.  Checking only at the toplevel is simpler, all we need
> to do is ensure that we get there every now and then (and that's what
> qemu_file_rate_limit does).
>
>>>> savevm.c: qemu_savevm_state_iterate()
>>>>
>>>>          if (qemu_file_rate_limit(f)) {
>>>>              return 0;
>>>>          }
>>>>
>>>> check is incorrect again, we should return an error if there is one
>>>> error.
>>> Nothing cares if qemu_savevm_state_iterate returns 0 or negative, so
>>> changing qemu_savevm_state_iterate to only return 0/1 would make sense too.
>> In this case, 0 means:
>>    please, call us again
>> when what we mean is:
>>    don't care about calling us again, there is an error.  Handle the error.
> Or alternatively, 0 means:
>
>     we haven't finished the work
>
> when what we mean is:
>
>     we haven't finished the work (BTW, please check if there is an error)
>
>> Notice that qemu_save_iterate() already returns errors in other code
>> paths
> Yes that's also unnecessary.
>
>> If we change th ereturn value for qemu_file_rate_limit() the change that
>> cames with this patch is not needed, that was my point.
> This is what an earlier patch from Lei did.  I told him (or her?) to

It's her. :)

> leave qemu_file_rate_limit aside since the idea behind QEMUFile is to
> only handle the error at the top.

Yes, I changed the return value for qemu_file_rate_limit() to negative for
that if there has been an error at the beginning. After the discussion with
Paolo, I think he's suggestion based on the idea that only handle error at
the top behind QEMUFile makes sense to me, so that's where this patch come
from.

>
> Paolo
>


-- 
Lei