Re: [Qemu-devel] [Qemu-block] [PATCH v2 0/3] block: Warn about usage of growing formats over non-growable protocols

[Paolo Bonzini]

On 06/05/2015 19:23, Max Reitz wrote:
> The guest sees whatever has been written into reply->error, and that
> field hasn't been written by this function in that case. It has been
> written by nbd_receive_reply() in nbd.c, and that value comes directly
> from the server. In case of qemu-nbd being the server, a write beyond
> the EOF should be caught by blk_check_byte_request() in
> block/block-backend.c, which returns -EIO. So that's where the EIO comes
> from.

Fair enough.  This makes sense, but then we have to create ENOSPC elsewhere.

> I don't know whether this EIO is subsequently converted to ENOSPC
> because of werror=enospc, but considering that
> https://bugzilla.redhat.com/show_bug.cgi?id=1090713 did not override
> werror, it doesn't look like it.

No, it shouldn't indeed.

Could alloc_clusters_noref do bdrv_truncate and return ENOSPC if it
fails?  That's how for example qcow and vhdx work.  vdi has the same
problem.

Paolo