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

[Markus Armbruster]

"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.