Re: [Qemu-devel] [PATCH 1/2] qemu-error: Introduce get_errno_name()

[Anthony Liguori]

On 05/04/2010 03:30 PM, Luiz Capitulino wrote:
>   StateVmSaveFailed is not like CommandFailed, there are five errors
> in do_savevm() and StateVmSaveFailed happens to be one of them.
>
>   But I understand what you mean and I have considered doing something
> like it, one of the problems though is that I'm not sure 'source' is
> enough to determine where the error has happened.
>
>   Consider do_savevm() again. We have three 'operations' that might
> fail: delete an existing snapshot, save the VM state and create the
> snapshot. All those operations can return -EIO as an error.
>    

Maybe those three operations should return distinct errnos?

That way, we can make more useful QErrors.

>   So, the first question is: would you map EIO to an QError? Just like
> you did for SocketIOError? If so, how would you know which operation
> has failed? Would you put its name in source? Or have an additional
> 'operation' key?
>
>   A related problem is not to degrade the current set of error messages
> we offer to the users. For do_savevm()'s 'save state' operation, current
> message is:
>
>     "Error -7 while writing VM"
>
>   With StateVmSaveFailed it becomes:
>
>     "Failed to save VM state ("EIO")"
>    

I don't think this is that useful to preserve because as you said, it 
could be one of three things.

Regards,

Anthony Liguori

>   Given the current implementation of QError, I'm not sure how we can have
> such a good error message if our QErrors are not 'operation based'.
>