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

[Christoph Hellwig]

> 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.

We have a mode where we stop the VM when it hits ENOSPC, and that is
the only reliably way to handle it.  One that ENOSPC gets returned
to the guest we don't know that it was an ENOSPC, and the guest will
usually simply shut the filesystem down.  This could be worked around
by implementing full T10 logical provisioning support, but very few
guests actually support it properly.  And it won't work with ide disks
at all, and for virtio we'd have to implement it first.