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

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Date:   Thu, 24 Oct 2019 11:31:04 +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 2019/10/24 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.


>
>>   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.

Thanks


>
> Alex
>
>> +	return 1;
>> +}
>> +
>>   /* Does namelen bytes of name exactly match the symbol? */
>>   static bool sym_is(const char *name, unsigned namelen, const char *symbol)
>>   {
>> @@ -1407,6 +1416,7 @@ static const struct devtable devtable[] = {
>>   	{"typec", SIZE_typec_device_id, do_typec_entry},
>>   	{"tee", SIZE_tee_client_device_id, do_tee_entry},
>>   	{"wmi", SIZE_wmi_device_id, do_wmi_entry},
>> +	{"mdev", SIZE_mdev_class_id, do_mdev_entry},
>>   };
>>   
>>   /* Create MODULE_ALIAS() statements.