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SubjectRe: [RFC PATCH 1/2] tracing/user_events: Use remote writes for event enablement
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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

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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