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Date: Wed, 13 Jan 2016 14:24:05 +0000
From: Bruce Richardson <bruce.richardson@intel.com>
To: Jan Viktorin <viktorin@rehivetech.com>
Message-ID: <20160113142405.GA7756@bricha3-MOBL3>
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Subject: Re: [dpdk-dev] [PATCH 03/14] eal/common: introduce union rte_device
 and related
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On Wed, Jan 13, 2016 at 03:12:27PM +0100, Jan Viktorin wrote:
> On Wed, 13 Jan 2016 14:01:19 +0000
> Bruce Richardson <bruce.richardson@intel.com> wrote:
> 
> > On Mon, Jan 04, 2016 at 09:08:15PM +0100, Jan Viktorin wrote:
> > > The union rte_device can be used in situations where we want to work with all
> > > devices without distinguishing among bus-specific features (PCI, ...).
> > > The target device type can be detected by reading the magic.
> > > 
> > > Also, the macros RTE_DEVICE_DECL and RTE_DEVICE_PTR_DECL are introduced to
> > > provide a generic way to declare a device or a pointer to a device. The macros
> > > aim to preserve API backwards-compatibility. Eg.
> > > 
> > > struct old_super_struct {             =>   struct old_super_struct {
> > >     struct rte_pci_device *pci_dev;   =>        RTE_DEVICE_PTR_DECL(pci_dev);
> > >     ...                               =>       ...
> > > };                                    =>   };
> > > 
> > > struct old_super_struct inst;
> > > 
> > > The new code should reference inst.dev.pci, the old code can still use the
> > > inst.pci_dev. The previously introduced magic is included so one can ask the
> > > instance about its type:
> > > 
> > > if (inst.dev.magic == RTE_PCI_DEVICE_MAGIC) {
> > >     ...
> > > }  
> > 
> > Rather than magic numbers i.e. #defines, an enum might be better.
> 
> True. However, would it be helpful to put really some _magic_ numbers
> there for debugging purposes (to clearly recognize the data type)? Or,
> is it sufficient to just say 1 for PCI, 2 for SoC, 3 for xxx...?
> 
I'd find it hard to see the need for actual magic numbers. I think the magic field
should be renamed to "type" and the values taken from a device_type enum. Should
make the code more readable e.g.

if (inst.dev.type == RTE_DEVTYPE_PCI) { ... }

/Bruce