[lttng-dev] [PATCH 2/2] Expose kernel tracer to user-space

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

* Francis Giraldeau (francis.giraldeau at gmail.com) wrote:
> By writing to the file /proc/lttng, a user-space application creates a
> kernel event. The event's payload is by default UTF-8 text, but any data
> can be written, up to 1024 bytes. Null-character is optional and is not
> enforced. The event uses sequence for space efficiency and to store any
> data as payload.

As discussed on IRC, please move the function to a separate module in
/probes/, and add a register function into lttng-abi.c that allows that
module to register its callback.

Thanks,

Mathieu

> 
> Signed-off-by: Francis Giraldeau <francis.giraldeau at gmail.com>
> ---
>  instrumentation/events/lttng-module/lttng.h |   21 +++++++++++++++++++++
>  lttng-abi.c                                 |   20 ++++++++++++++++++++
>  lttng-abi.h                                 |    1 +
>  3 files changed, 42 insertions(+)
> 
> diff --git a/instrumentation/events/lttng-module/lttng.h b/instrumentation/events/lttng-module/lttng.h
> index 6f3d6d1..cc36a8b 100644
> --- a/instrumentation/events/lttng-module/lttng.h
> +++ b/instrumentation/events/lttng-module/lttng.h
> @@ -28,6 +28,27 @@ TRACE_EVENT(lttng_metadata,
>  	TP_printk("")
>  )
>  
> +TRACE_EVENT(lttng_uevent,
> +
> +	TP_PROTO(const char *str, size_t len),
> +
> +	TP_ARGS(str, len),
> +
> +	/*
> +	 * Uses sequence to hold variable size data, by default considered
> +	 * as text. Null-terminal character is optional and is not enforced.
> +	 */
> +	TP_STRUCT__entry(
> +		__dynamic_array_text(char, text, len)
> +	),
> +
> +	TP_fast_assign(
> +		tp_memcpy_dyn_from_user(text, str)
> +	),
> +
> +	TP_printk("")
> +)
> +
>  #endif /*  _TRACE_LTTNG_H */
>  
>  /* This part must be outside protection */
> diff --git a/lttng-abi.c b/lttng-abi.c
> index 26a02ed..fa29e53 100644
> --- a/lttng-abi.c
> +++ b/lttng-abi.c
> @@ -50,6 +50,10 @@
>  #include "lttng-events.h"
>  #include "lttng-tracer.h"
>  
> +/* include our own uevent tracepoint */
> +#include "instrumentation/events/lttng-module/lttng.h"
> +DEFINE_TRACE(lttng_uevent);
> +
>  /*
>   * This is LTTng's own personal way to create a system call as an external
>   * module. We use ioctl() on /proc/lttng.
> @@ -252,9 +256,25 @@ long lttng_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>  	}
>  }
>  
> +/*
> + * lttng_write_uevent - expose kernel tracer to user-space
> + */
> +
> +static
> +ssize_t lttng_write_uevent(struct file *file, const char __user *user_buf,
> +		    size_t count, loff_t *fpos)
> +{
> +	if (count > LTTNG_UEVENT_SIZE)
> +		count = LTTNG_UEVENT_SIZE;
> +
> +	trace_lttng_uevent(user_buf, count);
> +	return count;
> +}
> +
>  static const struct file_operations lttng_fops = {
>  	.owner = THIS_MODULE,
>  	.unlocked_ioctl = lttng_ioctl,
> +	.write = lttng_write_uevent,
>  #ifdef CONFIG_COMPAT
>  	.compat_ioctl = lttng_ioctl,
>  #endif
> diff --git a/lttng-abi.h b/lttng-abi.h
> index dc230d8..f99b037 100644
> --- a/lttng-abi.h
> +++ b/lttng-abi.h
> @@ -26,6 +26,7 @@
>  #include <linux/fs.h>
>  
>  #define LTTNG_KERNEL_SYM_NAME_LEN	256
> +#define LTTNG_UEVENT_SIZE		1024
>  
>  enum lttng_kernel_instrumentation {
>  	LTTNG_KERNEL_TRACEPOINT	= 0,
> -- 
> 1.7.9.5
> 
> 
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com