Re: [Qemu-devel] [PATCH] block: prefer protocol_name over format_name in bdrv_iterate_format

[Jeff Cody]

On Thu, Apr 24, 2014 at 02:34:19PM +0200, Stefan Hajnoczi wrote:
> On Tue, Apr 15, 2014 at 04:00:54PM +0200, Kevin Wolf wrote:
> > Am 15.04.2014 um 15:28 hat Jeff Cody geschrieben:
> > > Some block drivers have multiple BlockDriver instances with identical
> > > format_name fields (e.g. gluster, nbd).  In those cases, the
> > > protocol_name is usually the more unique identifier (e.g. gluster+tcp).
> > > 
> > > Both qemu-img and qemu will use bdrv_iterate_format() to list the
> > > supported formats when a help option is invoked.  When just the
> > > format_name is used, redundant listings of formats occur (e.g.,
> > > "Supported formats: ... gluster gluster gluster gluster ... ").
> > > 
> > > If we prefer the protocol_name over the format_name (when the
> > > protocol name exists), then that provides a more informative
> > > help message:
> > > 
> > > "Supported formats: ... gluster gluster+tcp gluster+unix
> > > gluster+rdma ... "
> > > 
> > > Signed-off-by: Jeff Cody <address@hidden>
> > 
> > On the other hand, it means that you can't take any driver name from
> > here as use it as -drive driver=... value any more.
> 
> I think this change is problematic because of this.  It doesn't make
> sense that "Supported formats" lists names that actually
> bdrv_find_format() is unable to find.
> 
> blockdev_init()'s format= code will break if we make this change.
> 
> How about we change bdrv_iterate_format() to process unique format names
> only?  It doesn't make sense to process duplicate format names since the
> callback function has no way of identifying the specific BlockDriver
> from just the duplicate format name argument.
>

Yes, given the concern that blockdev_init()'s help output would be
misleading with this change, I think that is probably the best method
to go about it.