Re: [Qemu-devel] [PATCH] add bdrv->create function for host_device

[Nolan <nolan@sigbus.net>]

Anthony Liguori writes:
> I'm not quite sure how, but I think you need to have BDRV_O_FILE as a 
> special case.  I think probably the easiest thing to do is to bail
> out if BDRV_O_FILE is set since a physical device cannot be growable.

If I understand you correctly, my original patch already does that:

    if (flags || backing_file)
        return -ENOTSUP;

Though I can't say that I'm entirely sure I understand what it means to
pass BDRV_O_FILE to bdrv_create().

The consensus of other block_*.c implementations is to ignore flags
completely or bail if flags != 0, unless they have their own bdrv
specific flags (eg BLOCK_FLAG_COMPAT6 for vmdk, and BLOCK_FLAG_ENCRYPT
for qcow/qcow2) which they specifically honor and ignore any other
flags.