Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On 09/01/21 12:31, Greg KH wrote: Also considering that there will not be more than one copy of this device (it doesn't make sense as they would all do exactly the same thing), in this case a module parameter really seems to be the simplest way to configure it. So you never can have more than one of these in the system at one time? Because if this ever becomes not true, the module parameter is a mess... There shouldn't be. The device is only telling the host about panic-related events in the guest. The multiplexing of events to multiple interested listeners happens on the other side. Paolo
Re: [External] Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On 1/9/21 7:31 PM, Greg KH wrote: On Fri, Jan 08, 2021 at 04:26:17PM +0100, Paolo Bonzini wrote: On 08/01/21 16:15, Greg KH wrote: On Fri, Jan 08, 2021 at 04:04:24PM +0100, Paolo Bonzini wrote: On 08/01/21 15:07, Greg KH wrote: static void __iomem *base; +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; +module_param(events, uint, 0644); +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); I do not understand you wanting a module parameter as well as a sysfs file. Why is this needed? Why are you spreading this information out across different apis and locations? It can be useful to disable some functionality, for example in case you want to fake running on an older virtualization host. This can be done for debugging reasons, or to keep uniform handling across a fleet that is running different versions of QEMU. And where is this all going to be documented? I don't disagree. And what's wrong with just making the sysfs attribute writable? Isn't it harder to configure it at boot? Also the sysfs attribute added by patch 1 is documenting what is supported by the device, while the module parameter can be set to any value (you can think of the module parameter as of a "what to log" option, except the logging happens on another machine). But the module parameter is global, and not device specific. And yes, it would be harder to configure this at boot, is this something that is required? If so, please document that somewhere. Therefore, if you make the sysfs attribute writable, you would actually need _two_ attributes, one for the in-use capabilities and one for the device capabilities. And sysfs files are runtime values, which is different concept than 0444 module parameters (which are more like just configuration). That's not the module parameter mode setting in this patch :( So you would have to decide whether it's valid to write 2 to the in-use capabilities file when the device capabilities are "1", and I don't really have a good answer for that. Also considering that there will not be more than one copy of this device (it doesn't make sense as they would all do exactly the same thing), in this case a module parameter really seems to be the simplest way to configure it. So you never can have more than one of these in the system at one time? Because if this ever becomes not true, the module parameter is a mess... thanks, greg k-h What about adding _two_ device attribute: capability (0444): detect from device which the hypervisor really supports. events (0644): root user could enable/disable feature(s) from guest side. -- zhenwei pi
Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On Fri, Jan 08, 2021 at 04:26:17PM +0100, Paolo Bonzini wrote: > On 08/01/21 16:15, Greg KH wrote: > > On Fri, Jan 08, 2021 at 04:04:24PM +0100, Paolo Bonzini wrote: > > > On 08/01/21 15:07, Greg KH wrote: > > > > >static void __iomem *base; > > > > > +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; > > > > > +module_param(events, uint, 0644); > > > > > +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); > > > > I do not understand you wanting a module parameter as well as a sysfs > > > > file. Why is this needed? Why are you spreading this information out > > > > across different apis and locations? > > > > > > It can be useful to disable some functionality, for example in case you > > > want > > > to fake running on an older virtualization host. This can be done for > > > debugging reasons, or to keep uniform handling across a fleet that is > > > running different versions of QEMU. > > > > And where is this all going to be documented? > > I don't disagree. > > > And what's wrong with just making the sysfs attribute writable? > > Isn't it harder to configure it at boot? Also the sysfs attribute added by > patch 1 is documenting what is supported by the device, while the module > parameter can be set to any value (you can think of the module parameter as > of a "what to log" option, except the logging happens on another machine). But the module parameter is global, and not device specific. And yes, it would be harder to configure this at boot, is this something that is required? If so, please document that somewhere. > Therefore, if you make the sysfs attribute writable, you would actually need > _two_ attributes, one for the in-use capabilities and one for the device > capabilities. And sysfs files are runtime values, which is different > concept than 0444 module parameters (which are more like just > configuration). That's not the module parameter mode setting in this patch :( > So you would have to decide whether it's valid to write 2 > to the in-use capabilities file when the device capabilities are "1", and I > don't really have a good answer for that. > > Also considering that there will not be more than one copy of this device > (it doesn't make sense as they would all do exactly the same thing), in this > case a module parameter really seems to be the simplest way to configure it. So you never can have more than one of these in the system at one time? Because if this ever becomes not true, the module parameter is a mess... thanks, greg k-h
Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On 08/01/21 16:15, Greg KH wrote: On Fri, Jan 08, 2021 at 04:04:24PM +0100, Paolo Bonzini wrote: On 08/01/21 15:07, Greg KH wrote: static void __iomem *base; +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; +module_param(events, uint, 0644); +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); I do not understand you wanting a module parameter as well as a sysfs file. Why is this needed? Why are you spreading this information out across different apis and locations? It can be useful to disable some functionality, for example in case you want to fake running on an older virtualization host. This can be done for debugging reasons, or to keep uniform handling across a fleet that is running different versions of QEMU. And where is this all going to be documented? I don't disagree. And what's wrong with just making the sysfs attribute writable? Isn't it harder to configure it at boot? Also the sysfs attribute added by patch 1 is documenting what is supported by the device, while the module parameter can be set to any value (you can think of the module parameter as of a "what to log" option, except the logging happens on another machine). Therefore, if you make the sysfs attribute writable, you would actually need _two_ attributes, one for the in-use capabilities and one for the device capabilities. And sysfs files are runtime values, which is different concept than 0444 module parameters (which are more like just configuration). So you would have to decide whether it's valid to write 2 to the in-use capabilities file when the device capabilities are "1", and I don't really have a good answer for that. Also considering that there will not be more than one copy of this device (it doesn't make sense as they would all do exactly the same thing), in this case a module parameter really seems to be the simplest way to configure it. Paolo
Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On Fri, Jan 08, 2021 at 04:04:24PM +0100, Paolo Bonzini wrote: > On 08/01/21 15:07, Greg KH wrote: > > > static void __iomem *base; > > > +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; > > > +module_param(events, uint, 0644); > > > +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); > > I do not understand you wanting a module parameter as well as a sysfs > > file. Why is this needed? Why are you spreading this information out > > across different apis and locations? > > It can be useful to disable some functionality, for example in case you want > to fake running on an older virtualization host. This can be done for > debugging reasons, or to keep uniform handling across a fleet that is > running different versions of QEMU. And where is this all going to be documented? And what's wrong with just making the sysfs attribute writable? thanks, greg k-h
Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On 08/01/21 15:07, Greg KH wrote: static void __iomem *base; +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; +module_param(events, uint, 0644); +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); I do not understand you wanting a module parameter as well as a sysfs file. Why is this needed? Why are you spreading this information out across different apis and locations? It can be useful to disable some functionality, for example in case you want to fake running on an older virtualization host. This can be done for debugging reasons, or to keep uniform handling across a fleet that is running different versions of QEMU. Paolo Again, adding module parameters is almost never a good idea anymore, they are a pain to manage and use.
Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
On Fri, Jan 08, 2021 at 09:52:23PM +0800, zhenwei pi wrote: > Suggested by Paolo, add a module parameter 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 > --- > drivers/misc/pvpanic.c | 6 +- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c > index e1023c7b8fb0..417f1086e764 100644 > --- a/drivers/misc/pvpanic.c > +++ b/drivers/misc/pvpanic.c > @@ -19,6 +19,10 @@ > #include > > static void __iomem *base; > +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED; > +module_param(events, uint, 0644); > +MODULE_PARM_DESC(events, "set event limitation of pvpanic device"); I do not understand you wanting a module parameter as well as a sysfs file. Why is this needed? Why are you spreading this information out across different apis and locations? Again, adding module parameters is almost never a good idea anymore, they are a pain to manage and use. thanks, greg k-h
[PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'
Suggested by Paolo, add a module parameter 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
---
drivers/misc/pvpanic.c | 6 +-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
index e1023c7b8fb0..417f1086e764 100644
--- a/drivers/misc/pvpanic.c
+++ b/drivers/misc/pvpanic.c
@@ -19,6 +19,10 @@
#include
static void __iomem *base;
+static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
+module_param(events, uint, 0644);
+MODULE_PARM_DESC(events, "set event limitation of pvpanic device");
+
static unsigned int capability = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
static ssize_t capability_show(struct device *dev,
@@ -48,7 +52,7 @@ MODULE_LICENSE("GPL");
static void
pvpanic_send_event(unsigned int event)
{
- if (event & capability)
+ if (event & capability & events)
iowrite8(event, base);
}
--
2.25.1
