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Re: [Qemu-devel] [PATCH v2] qdev: don't add typename to fw_dev_path when

From: Amos Kong
Subject: Re: [Qemu-devel] [PATCH v2] qdev: don't add typename to fw_dev_path when get_fw_dev_path isn't implemented
Date: Wed, 29 May 2013 12:41:37 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, May 28, 2013 at 01:15:57PM +0200, Paolo Bonzini wrote:
> Il 28/05/2013 13:00, Amos Kong ha scritto:
> > Recent virtio refactoring in QEMU made virtio-bus become the parent bus
> > of scsi-bus, and virtio-bus doesn't have get_fw_dev_path implementation,
> > so redundant typename will be added to fw_dev_path. It causes that
> > bootindex parameter of scsi device doesn't work.
> > 
> > This patch changes qdev_get_fw_dev_path_helper() to add nothing if
> > implemented get_fw_dev_path() returns NULL.
> > 
> > Signed-off-by: Amos Kong <address@hidden>
> > --
> > v2: only add nothing to fw_dev_path when get_fw_dev_path() is
> >     implemented and return NULL. then it will not effect other devices
> >     don't have get_fw_dev_path() implementation.

Hi Paolo,
> To achieve the same result, you can simply ensure that all classes
> implement the method.

Do you mean if some classes didn't have an implement, I need to add
a implement (just returns NULL) for all of them, then nothing will be
added to fw_dev_path for those classes?

Currently I'm sure 'typename' is redundant for virio-bus. 'typename'
might be needed for other class (have no get_fw_dev_path implementation)

Applied patch v2, there are three conditions: 
 1) implement get_fw_dev_path, return specific string, add to
    fw_dev_path (same as original)
 2) don't implement get_fw_dev_path, add typename to fw_dev_path.
    (same as original)
 3) implement get_fw_dev_path and return NULL, nothing is added
    to fw_dev_path (new behavior)

If some other class wants to add nothing to path, just define a method
to return NULL.

> The default implementation is just
> g_strdup(object_get_typename(OBJECT(dev))).

If we implement the method for all classes, the default implementation
in qdev_get_fw_dev_path_helper() will not be called.
> Remember that if you do not specify a method in a BusClass's class_init
> function, it is inherited from the superclass.
> Paolo


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