Re: [Qemu-devel] [PATCH 0/3] Fix confused output for alias properties

[Gonglei (Arei)]

> From: Markus Armbruster [mailto:address@hidden
> Sent: Tuesday, September 16, 2014 3:21 PM
> To: Michael S. Tsirkin
> Subject: Re: [Qemu-devel] [PATCH 0/3] Fix confused output for alias properties
> 
> "Michael S. Tsirkin" <address@hidden> writes:
> 
> > On Mon, Sep 15, 2014 at 05:57:51PM +0200, Paolo Bonzini wrote:
> >> Il 15/09/2014 16:44, address@hidden ha scritto:
> >> > From: Gonglei <address@hidden>
> >> >
> >> > At present, people have no way to know they should
> >> > have a specific format for alias properties.
> >> >
> >> >  Example:
> >> >
> >> > before output:
> >> >
> >> > virtio-blk-pci.physical_block_size=uint16
> >> > virtio-blk-pci.logical_block_size=uint16
> >> > virtio-blk-pci.drive=str
> >> >
> >> > after output applied this patch series:
> >> >
> >> > virtio-blk-pci.physical_block_size=blocksize
> >> > virtio-blk-pci.logical_block_size=blocksize
> >> > virtio-blk-pci.drive=drive
> >>
> >> Is there actually anyone that is relying on the legacy_names of
> >> properties?  I would be inclined to drop them altogether...
> >>
> >> Paolo
> >
> > What makes these legacy?
> 
> Rebasing qdev on top of QOM produced a bit of cruft.
> 
> PropertyInfo defines a kind of property.  It used to look like this:
> 
>     struct PropertyInfo {
>         const char *name;
>         size_t size;
>         enum PropertyType type;
>         int (*parse)(DeviceState *dev, Property *prop, const char *str);
>         int (*print)(DeviceState *dev, Property *prop, char *dest, size_t 
> len);
>     };
> 
> Lets generic code parse, unparse and copy properties.
> 
> Commit 922910c added the -device FOO,? feature, using member name to
> give a hint on possible property values.
> 
> The rebase onto QOM renamed name to legacy_name, to free name for use as
> QOM type name (commit cafe5bd).
> 
> Current code uses legacy_name as follows:
> 
> * QMP command device-list-properties
> 
>   Returns a list of DevicePropertyInfo, whose member "type" is
>   PropertyInfo's legacy_name if set, else its name.
> 
> * -device FOO,help
> 
>   Prints FOO.NAME=TYPE, where NAME is the property's name (not to be
>   confused with PropertyInfo's name), and TYPE is PropertyInfo's legacy
>   name if set, else its name.
> 
>   -device FOO,? is an outmoded way to say -device FOO,help.  No plans to
>   drop support for it.
> 
> The second is actually built on top of the first.
> 
> > How do you expect users to find out about the properties?
> >>qemu -device virtio-blk-pci.?
> > is not the correct way anymore?
> 
> As far as I can tell, libvirt uses both device-list-properties and
> "-device,?".  It doesn't appear to use the returned "type".
> 
> Human users do, however.  I'd object to a degradation of -device
> FOO,help.  Changing it is fine, but it should remain at least as helpful
> as it is now.
> 
> > How the time flies, it seems only yesterday this was the
> > new way, -help was the old one ...
> 
> Everything must change, so that everything can stay the same.

What detailed explanation it is! Thanks. :)

Best regards,
-Gonglei