linux-kernel - Re: [PATCH V5 2/6] modpost: add support for mdev class id

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Date:   Fri, 25 Oct 2019 09:44:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
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Subject: Re: [PATCH V5 2/6] modpost: add support for mdev class id


On 2019/10/25 上午3:54, Alex Williamson wrote:
> On Thu, 24 Oct 2019 11:31:04 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
>> On 2019/10/24 上午5:42, Alex Williamson wrote:
>>> On Wed, 23 Oct 2019 21:07:48 +0800
>>> Jason Wang <jasowang@...hat.com> wrote:
>>>   
>>>> Add support to parse mdev class id table.
>>>>
>>>> Reviewed-by: Parav Pandit <parav@...lanox.com>
>>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>>>> ---
>>>>    drivers/vfio/mdev/vfio_mdev.c     |  2 ++
>>>>    scripts/mod/devicetable-offsets.c |  3 +++
>>>>    scripts/mod/file2alias.c          | 10 ++++++++++
>>>>    3 files changed, 15 insertions(+)
>>>>
>>>> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
>>>> index 7b24ee9cb8dd..cb701cd646f0 100644
>>>> --- a/drivers/vfio/mdev/vfio_mdev.c
>>>> +++ b/drivers/vfio/mdev/vfio_mdev.c
>>>> @@ -125,6 +125,8 @@ static const struct mdev_class_id id_table[] = {
>>>>    	{ 0 },
>>>>    };
>>>>    
>>>> +MODULE_DEVICE_TABLE(mdev, id_table);
>>>> +
>>> Two questions, first we have:
>>>
>>> #define MODULE_DEVICE_TABLE(type, name)                                 \
>>> extern typeof(name) __mod_##type##__##name##_device_table               \
>>>     __attribute__ ((unused, alias(__stringify(name))))
>>>
>>> Therefore we're defining __mod_mdev__id_table_device_table with alias
>>> id_table.  When the virtio mdev bus driver is added in 5/6 it uses the
>>> same name value.  I see virtio types all register this way (virtio,
>>> id_table), so I assume there's no conflict, but pci types mostly (not
>>> entirely) seem to use unique names.  Is there a preference to one way
>>> or the other or it simply doesn't matter?
>>
>> It looks to me that those symbol were local, so it doesn't matter. But
>> if you wish I can switch to use unique name.
> I don't have a strong opinion, I'm just trying to make sure we're not
> doing something obviously broken.


Yes, to be more safe I will switch to unique names here.


>
>>>>    static struct mdev_driver vfio_mdev_driver = {
>>>>    	.name	= "vfio_mdev",
>>>>    	.probe	= vfio_mdev_probe,
>>>> diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
>>>> index 054405b90ba4..6cbb1062488a 100644
>>>> --- a/scripts/mod/devicetable-offsets.c
>>>> +++ b/scripts/mod/devicetable-offsets.c
>>>> @@ -231,5 +231,8 @@ int main(void)
>>>>    	DEVID(wmi_device_id);
>>>>    	DEVID_FIELD(wmi_device_id, guid_string);
>>>>    
>>>> +	DEVID(mdev_class_id);
>>>> +	DEVID_FIELD(mdev_class_id, id);
>>>> +
>>>>    	return 0;
>>>>    }
>>>> diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
>>>> index c91eba751804..d365dfe7c718 100644
>>>> --- a/scripts/mod/file2alias.c
>>>> +++ b/scripts/mod/file2alias.c
>>>> @@ -1335,6 +1335,15 @@ static int do_wmi_entry(const char *filename, void *symval, char *alias)
>>>>    	return 1;
>>>>    }
>>>>    
>>>> +/* looks like: "mdev:cN" */
>>>> +static int do_mdev_entry(const char *filename, void *symval, char *alias)
>>>> +{
>>>> +	DEF_FIELD(symval, mdev_class_id, id);
>>>> +
>>>> +	sprintf(alias, "mdev:c%02X", id);
>>> A lot of entries call add_wildcard() here, should we?  Sorry for the
>>> basic questions, I haven't played in this code.  Thanks,
>>
>> It's really good question. My understanding is we won't have a module
>> that can deal with all kinds of classes like CLASS_ID_ANY. So there's
>> probably no need for the wildcard.
> The comment for add_wildcard() indicates future extension, so it's hard
> to know what we might need in the future until we do need it.  The
> majority of modules.alias entries on my laptop (even if I exclude pci
> aliases) end with a wildcard.  Thanks,


Yes, so I will add that for future extension.

Thanks


>
> Alex
>