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

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Message-ID: <20191024135441.160daa56@x1.home>
Date:   Thu, 24 Oct 2019 13:54:41 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
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Subject: Re: [PATCH V5 2/6] modpost: add support for mdev class id

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.

> >>   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,

Alex