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

Francis Giraldeau francis.giraldeau at gmail.com
Tue Jun 5 19:40:33 EDT 2012

Le 2012-06-06 01:24, Francis Giraldeau a écrit :
> 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.
> Update: split the probe code into it's own module and make it an optional
> feature of lttng-abi. The feature is enabled when the module is loaded. The
> lttng-abi module exports a register function and includes a wrapper for
> lttng_fops write. This is required since struct file_operations must be const.
> Since the module dependency is reversed, unloading the lttng-uevent module is
> done only when it's not used anymore. This is done with rwlock synchronisation.
> The synchronisation doesn't prevent starvation, but this situation is unlikely
> and can be prevented by stop active tracing sessions.

One little gotcha: after modprobe lttng-uevent, the module
lttng-probe-uevent must be loaded manually, otherwise lttng_uevent is
not listed with "lttng list -k". Is there a way to make the probe load
automatically when lttng-uevent is loaded?



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