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    SubjectRe: [PATCH v4 2/2] misc: pvpanic: introduce events device attribue
    On Sun, Jan 10, 2021 at 01:37:19PM +0800, zhenwei pi wrote:
    > Suggested by Paolo & Greg, add 'events' device attribute that can be
    > used to limit which capabilities the driver uses.
    >
    > Finally, the pvpanic guest driver works by the limitation of both
    > device capability and user setting.
    >
    > Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
    > ---
    > .../ABI/testing/sysfs-bus-pci-devices-pvpanic | 7 +++++
    > drivers/misc/pvpanic.c | 26 ++++++++++++++++++-
    > 2 files changed, 32 insertions(+), 1 deletion(-)
    >
    > diff --git a/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
    > index 57d014a2c339..4750cfa0af2b 100644
    > --- a/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
    > +++ b/Documentation/ABI/testing/sysfs-bus-pci-devices-pvpanic
    > @@ -5,3 +5,10 @@ Description:
    > Read-only attribute. Capabilities of pvpanic device
    > which are supported by QEMU.
    > Format: %s.
    > +
    > +What: /sys/devices/pci0000:00/*/QEMU0001:00/events
    > +Date: Jan 2021
    > +Contact: zhenwei pi <pizhenwei@bytedance.com>
    > +Description:
    > + RW attribute. Set/get which features in-use.
    > + Format: %x.

    Please describe the allowed values.

    > diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
    > index c2f6a9e866b3..07a008e15bd2 100644
    > --- a/drivers/misc/pvpanic.c
    > +++ b/drivers/misc/pvpanic.c
    > @@ -19,8 +19,31 @@
    > #include <uapi/misc/pvpanic.h>
    >
    > static void __iomem *base;
    > +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
    > static unsigned int capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
    >
    > +static ssize_t events_show(struct device *dev, struct device_attribute *attr, char *buf)
    > +{
    > + return sprintf(buf, "%x\n", events);
    > +}
    > +
    > +static ssize_t events_store(struct device *dev, struct device_attribute *attr,
    > + const char *buf, size_t count)
    > +{
    > + unsigned int tmp;
    > + int err;
    > +
    > + err = kstrtouint(buf, 16, &tmp);
    > + if (err)
    > + return err;
    > +
    > + events = tmp;
    > +
    > + return count;
    > +
    > +}
    > +static DEVICE_ATTR_RW(events);
    > +
    > static ssize_t capability_show(struct device *dev,
    > struct device_attribute *attr, char *buf)
    > {
    > @@ -32,6 +55,7 @@ static DEVICE_ATTR_RO(capability);
    >
    > static struct attribute *pvpanic_dev_attrs[] = {
    > &dev_attr_capability.attr,
    > + &dev_attr_events.attr,
    > NULL
    > };
    > ATTRIBUTE_GROUPS(pvpanic_dev);
    > @@ -43,7 +67,7 @@ MODULE_LICENSE("GPL");
    > static void
    > pvpanic_send_event(unsigned int event)
    > {
    > - if (event & capability)
    > + if (event & capability & events)

    That's just going to be so crazy to try to figure out, I'm glad I'm not
    a user trying to configure this.

    User apis are hard.

    thanks,

    greg k-h

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