Re: [Qemu-devel] [PATCH v2 0/5]: QMP: Proper thin provisioning support

[Kevin Wolf <kwolf@redhat.com>]

Am 03.08.2011 17:19, schrieb Luiz Capitulino:
> Roughly speaking, thin provisioning is a feature where the VM is started with
> a small disk and space is allocated on demand.
> 
> It's already possible for QMP clients to implement this feature by using
> the BLOCK_IO_ERROR event. However, the event can be missed. When this
> happens QMP clients need a way to query if any block device has hit a
> no space condition.
> 
> This is what this series is about: it extends the query-block command to
> contain the disk's I/O status.
> 
> Please, note that this series depends on the following two other series:
> 
>  1. [PATCH 00/55] Block layer cleanup & fixes (by Markus)
>  2. [PATCH 0/7]: Introduce the QemuState type (by me)

It feels strange that device models are involved with this. The block
layer already knows the error number, it just tells the device model so
that it can ask it back. Wouldn't it be easier to store it in the
BlockDriverState?

Also, as I already commented on v1, I think it's a bad idea to let
requests that complete later overwrite the error code with "success".
Quite possible in an ENOSPC case, I think.

Kevin