Re: [PATCH] perf_event_open.2: 4.9 PERF_EVENT_IOC_SET_DRV_CONFIGS support

On Thu, 11 Aug 2016, Mathieu Poirier wrote:

+.TP
+.BR PERF_EVENT_IOC_SET_DRV_CONFIGS " (since Linux 4.9)"
+This makes it possible to pass configuration parameters to PMU drivers.
+Configuration parameters are specific to each drivers.
+
+The argument is a pointer to the desired configuration parameters.

So I gave up and read the code and I'm guessing this is what you really 
mean:

.TP
.BR PERF_EVENT_IOC_SET_DRV_CONFIGS " (since Linux 4.9)"
Pass custom configuration paramaters to a PMU driver.

The argument is a pointer to a NUL-termiated string of up to
PAGE_SIZE in length.
The string contains a list of comma-separated configuration options
that will be parsed by the kernel.
The kernel handles both singleton values as well as name/value pairs
that are indicated with the '=' character.
The size of the strings is limited internally to PERF_DRV_CONFIG_MAX
(which is not visible to userspace).



some additional questions: can this ioctl be run at any time or should it 
only be run while the event is quiet?  Does the change in options take
place immediately?

Vince
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