linux-kernel - Re: [PATCH v9 10/12] vfio: Add function to get device_api string from vfio_device

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Message-ID: <c9a21204-bb25-6d89-a519-5b93e6c4456d@nvidia.com>
Date:   Fri, 21 Oct 2016 01:59:55 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     <pbonzini@...hat.com>, <kraxel@...hat.com>, <cjia@...dia.com>,
        <qemu-devel@...gnu.org>, <kvm@...r.kernel.org>,
        <kevin.tian@...el.com>, <jike.song@...el.com>,
        <bjsdjshi@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 10/12] vfio: Add function to get device_api string from
 vfio_device_info.flags



On 10/21/2016 1:04 AM, Alex Williamson wrote:
> On Tue, 18 Oct 2016 02:52:10 +0530
> Kirti Wankhede <kwankhede@...dia.com> wrote:
> 
>> Function vfio_device_api_string() returns string based on flag set in
>> vfio_device_info's flag. This should be used by vendor driver to get string
>> based on flag for device_api attribute.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@...dia.com>
>> Signed-off-by: Neo Jia <cjia@...dia.com>
>> Change-Id: I42d29f475f02a7132ce13297fbf2b48f1da10995
>> ---
>>  drivers/vfio/vfio.c  | 15 +++++++++++++++
>>  include/linux/vfio.h |  2 ++
>>  2 files changed, 17 insertions(+)
>>
>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>> index 10ef1c5fa762..aec470454a13 100644
>> --- a/drivers/vfio/vfio.c
>> +++ b/drivers/vfio/vfio.c
>> @@ -1917,6 +1917,21 @@ int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, int num_irqs,
>>  }
>>  EXPORT_SYMBOL(vfio_set_irqs_validate_and_prepare);
>>  
>> +const char *vfio_device_api_string(u32 flags)
>> +{
>> +	if (flags & VFIO_DEVICE_FLAGS_PCI)
>> +		return "vfio-pci";
>> +
>> +	if (flags & VFIO_DEVICE_FLAGS_PLATFORM)
>> +		return "vfio-platform";
>> +
>> +	if (flags & VFIO_DEVICE_FLAGS_AMBA)
>> +		return "vfio-amba";
>> +
>> +	return "";
>> +}
>> +EXPORT_SYMBOL(vfio_device_api_string);
>> +
>>  /*
>>   * Pin a set of guest PFNs and return their associated host PFNs for local
>>   * domain only.
>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index 31d059f1649b..fca2bf23c4f1 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -116,6 +116,8 @@ extern int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr,
>>  					      int num_irqs, int max_irq_type,
>>  					      size_t *data_size);
>>  
>> +extern const char *vfio_device_api_string(u32 flags);
>> +
>>  struct pci_dev;
>>  #ifdef CONFIG_EEH
>>  extern void vfio_spapr_pci_eeh_open(struct pci_dev *pdev);
> 
> Couldn't this simply be a #define in the uapi header?
> 
> #define VFIO_DEVICE_PCI_API_STRING "vfio-pci"
> 
> I don't really see why we need a lookup function.
> 

String is tightly coupled with the FLAG, right?
Instead user need to take care of making sure to return proper string,
and don't mis-match the string, I think having function is easier.
Vendor driver should decide the type of device they want to expose and
set the flag, using this function vendor driver would return string
which is based on flag they set.

Kirti