Re: [PATCH] vdpa: add driver_override support

[Jason Wang]

On Fri, Nov 5, 2021 at 4:05 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> On Fri, Nov 05, 2021 at 11:01:30AM +0800, Jason Wang wrote:
> >On Fri, Nov 5, 2021 at 12:17 AM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
> >>
> >> `driver_override` allows to control which of the vDPA bus drivers
> >> binds to a vDPA device.
> >>
> >> If `driver_override` is not set, the previous behaviour is followed:
> >> devices use the first vDPA bus driver loaded (unless auto binding
> >> is disabled).
> >>
> >> Tested on Fedora 34 with driverctl(8):
> >>   $ modprobe virtio-vdpa
> >>   $ modprobe vhost-vdpa
> >>   $ modprobe vdpa-sim-net
> >>
> >>   $ vdpa dev add mgmtdev vdpasim_net name dev1
> >>
> >>   # dev1 is attached to the first vDPA bus driver loaded
> >>   $ driverctl -b vdpa list-devices
> >>     dev1 virtio_vdpa
> >>
> >>   $ driverctl -b vdpa set-override dev1 vhost_vdpa
> >>
> >>   $ driverctl -b vdpa list-devices
> >>     dev1 vhost_vdpa [*]
> >>
> >>   Note: driverctl(8) integrates with udev so the binding is
> >>   preserved.
> >>
> >> Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
> >> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> >> ---
> >>  include/linux/vdpa.h |  2 ++
> >>  drivers/vdpa/vdpa.c  | 74 ++++++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 76 insertions(+)
> >>
> >> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> >> index c3011ccda430..ae34015b37b7 100644
> >> --- a/include/linux/vdpa.h
> >> +++ b/include/linux/vdpa.h
> >> @@ -64,6 +64,7 @@ struct vdpa_mgmt_dev;
> >>   * struct vdpa_device - representation of a vDPA device
> >>   * @dev: underlying device
> >>   * @dma_dev: the actual device that is performing DMA
> >> + * @driver_override: driver name to force a match
> >
> >This seems useless?
>
> I'm a bit lost, do you mean we should remove the documentation of
> `driver_override`?

I misread the code which was misled by vdpa_mgmt_dev above:(

The code should be fine.

So:

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

>
> >
> >>   * @config: the configuration ops for this device.
> >>   * @cf_mutex: Protects get and set access to configuration layout.
> >>   * @index: device index
> >> @@ -76,6 +77,7 @@ struct vdpa_mgmt_dev;
> >>  struct vdpa_device {
> >>         struct device dev;
> >>         struct device *dma_dev;
> >> +       const char *driver_override;
> >>         const struct vdpa_config_ops *config;
> >>         struct mutex cf_mutex; /* Protects get/set config */
> >>         unsigned int index;
> >> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> >> index 7332a74a4b00..659231bbfee8 100644
> >> --- a/drivers/vdpa/vdpa.c
> >> +++ b/drivers/vdpa/vdpa.c
> >> @@ -52,8 +52,81 @@ static void vdpa_dev_remove(struct device *d)
> >>                 drv->remove(vdev);
> >>  }
> >>
> >> +static int vdpa_dev_match(struct device *dev, struct device_driver *drv)
> >> +{
> >> +       struct vdpa_device *vdev = dev_to_vdpa(dev);
> >> +
> >> +       /* Check override first, and if set, only use the named driver */
> >> +       if (vdev->driver_override)
> >> +               return strcmp(vdev->driver_override, drv->name) == 0;
> >> +
> >> +       /* Currently devices must be supported by all vDPA bus
> >> drivers */
> >> +       return 1;
> >> +}
> >> +
> >> +static ssize_t driver_override_store(struct device *dev,
> >> +                                    struct device_attribute *attr,
> >> +                                    const char *buf, size_t count)
> >> +{
> >> +       struct vdpa_device *vdev = dev_to_vdpa(dev);
> >> +       const char *driver_override, *old;
> >> +       char *cp;
> >> +
> >> +       /* We need to keep extra room for a newline */
> >> +       if (count >= (PAGE_SIZE - 1))
> >> +               return -EINVAL;
> >> +
> >> +       driver_override = kstrndup(buf, count, GFP_KERNEL);
> >> +       if (!driver_override)
> >> +               return -ENOMEM;
> >> +
> >> +       cp = strchr(driver_override, '\n');
> >> +       if (cp)
> >> +               *cp = '\0';
> >> +
> >> +       device_lock(dev);
> >> +       old = vdev->driver_override;
> >> +       if (strlen(driver_override)) {
> >> +               vdev->driver_override = driver_override;
> >> +       } else {
> >> +               kfree(driver_override);
> >> +               vdev->driver_override = NULL;
> >> +       }
> >> +       device_unlock(dev);
> >> +
> >> +       kfree(old);
> >> +
> >> +       return count;
> >> +}
> >> +
> >> +static ssize_t driver_override_show(struct device *dev,
> >> +                                   struct device_attribute *attr, char *buf)
> >> +{
> >> +       struct vdpa_device *vdev = dev_to_vdpa(dev);
> >> +       ssize_t len;
> >> +
> >> +       device_lock(dev);
> >> +       len = snprintf(buf, PAGE_SIZE, "%s\n", vdev->driver_override);
> >> +       device_unlock(dev);
> >> +
> >> +       return len;
> >> +}
> >> +static DEVICE_ATTR_RW(driver_override);
> >> +
> >> +static struct attribute *vdpa_dev_attrs[] = {
> >> +       &dev_attr_driver_override.attr,
> >> +       NULL,
> >> +};
> >> +
> >> +static const struct attribute_group vdpa_dev_group = {
> >> +       .attrs  = vdpa_dev_attrs,
> >> +};
> >> +__ATTRIBUTE_GROUPS(vdpa_dev);
> >> +
> >>  static struct bus_type vdpa_bus = {
> >>         .name  = "vdpa",
> >> +       .dev_groups = vdpa_dev_groups,
> >
> >This reminds me that we probably need to document the sysfs interface
> >in Documentation/ABI/testing/sysfs-bus-vdpa.
> >
>
> Yeah, I'd like to add more documentation. We should also document the
> device life cycle and management API.
>
> It's on my to-do list, I'm prioritizing it!
>
> >But it's not the fault of this patch which look good.
>
> Thanks,
> Stefano
>