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SubjectRe: [RFC PATCH 1/2] tracing/user_events: Use remote writes for event enablement
On Sat, Oct 29, 2022 at 10:44:32AM -0400, Mathieu Desnoyers wrote:
> On 2022-10-27 18:40, Beau Belgrave wrote:
>
> [...]
> > diff --git a/include/linux/user_events.h b/include/linux/user_events.h
> > index 592a3fbed98e..4c3bd16395a9 100644
> > --- a/include/linux/user_events.h
> > +++ b/include/linux/user_events.h
> > @@ -33,12 +33,16 @@ struct user_reg {
> > /* Input: Size of the user_reg structure being used */
> > __u32 size;
> > + /* Input: Flags/common settings */
> > + __u32 enable_bit : 5, /* Bit in enable address to use (0-31) */
> > + __reserved : 27;
>
> I'm always worried about using C/C++ bitfields in uapi, because some
> compilers (e.g. MS Windows Compiler) have different implementation of the
> bitfields. See
>
> gcc(1)
>
> -Wnopacked-bitfield-compat
> -mms-bitfields / -mno-ms-bitfields
>

Sure, I'll change this __u8.

> Thanks,
>
> Mathieu
>
> > +
> > + /* Input: Address to update when enabled */
> > + __u64 enable_addr;
> > +
> > /* Input: Pointer to string with event name, description and flags */
> > __u64 name_args;
> > - /* Output: Bitwise index of the event within the status page */
> > - __u32 status_bit;
> > -
> > /* Output: Index of the event to use when writing data */
> > __u32 write_index;
> > } __attribute__((__packed__));
> > diff --git a/kernel/trace/trace_events_user.c
> > b/kernel/trace/trace_events_user.c--
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com

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