[lttng-dev] [RFC PATCH lttng-tools] Fix printk instrumentation

[Yannick Brosseau]

On 2013-07-04 12:58, Mathieu Desnoyers wrote:
> This patch fixes the printk instrumentation.
>
> - It does not require a 2kB buffer on the stack anymore,
> - It introduces __dynamic_array_enc_ext_2() and tp_memcpy_dyn_2(), which
>   allow copying into a single variable-length buffer from two sources,
>   useful for kernel < 3.5.
> - It adds support for 3.10 kernel printk instrumentation.
>
> Yannick, can you try this out on 3.4, 3.5, 3.9 and 3.10 kernels ? When
> you confirm that it works, I'll split it into two patches (one for
> lttng-events.h and the other for printk.h), merge, and backport this.
So far:
3.10: Works and compile when small typo fixed (see bellow)
3.9: Works
3.2: Fail to enable with this error msg (will try to get more detailled
info or fix)
root at debian-wheezy:/home/scientist# lttng enable-event -k console
PERROR [6648/6745]: create event ioctl: Invalid argument (in
kernel_create_event() at kernel.c:205)
Error: Event console: Enable kernel event failed (channel channel0,
session auto-20130630-135404)
Warning: Some command(s) went wrong


> Only built-tested on 3.5 kernel so far.
>
> Thanks,
>
> Mathieu
>
> ---
> diff --git a/instrumentation/events/lttng-module/printk.h b/instrumentation/events/lttng-module/printk.h
> index 4c744f9..e22a2cc 100644
> --- a/instrumentation/events/lttng-module/printk.h
> +++ b/instrumentation/events/lttng-module/printk.h
> @@ -7,7 +7,25 @@
>  #include <linux/tracepoint.h>
>  #include <linux/version.h>
>  
> -#define MSG_TRACE_MAX_LEN	2048
> +#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,10,0))
> +
> +TRACE_EVENT(console,
> +	TP_PROTO(const char *text, size_t len),
> +
> +	TP_ARGS(text, len),
> +
> +	TP_STRUCT__entry(
> +		__dynamic_array_text(char, msg, len)
> +	),
> +
> +	TP_fast_assign(
> +		tp_memcpy_dyn(msg, msg)
>
second "msg" should be "text"