From ca19ed4d1fdb51e33314f701b041f1da537d09db Mon Sep 17 00:00:00 2001 From: Philippe Proulx Date: Thu, 2 Apr 2020 11:59:02 -0400 Subject: [PATCH] 2.11: document `/dev/lttng-logger` feature See LTTng-modules's 4d32837 ("Add a new /dev/lttng-logger interface") commit. Signed-off-by: Philippe Proulx --- 2.11/lttng-docs-2.11.txt | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/2.11/lttng-docs-2.11.txt b/2.11/lttng-docs-2.11.txt index b824f5a..6af6a7b 100644 --- a/2.11/lttng-docs-2.11.txt +++ b/2.11/lttng-docs-2.11.txt @@ -1,7 +1,7 @@ The LTTng Documentation ======================= Philippe Proulx -v2.11, 30 March 2020 +v2.11, 2 April 2020 include::../common/copyright.txt[] @@ -202,6 +202,14 @@ address. + This change makes the tracer more efficient on NUMA systems. +* The <> kernel module now also + creates a ``misc'' device named `lttng-logger`, which udev will + make accessible as the path:{/dev/lttng-logger} special file. ++ +The `lttng-logger` device shares the `/proc/lttng-logger` file's ABI, +but it works from within containers when the path is made accessible to +them. + [[nuts-and-bolts]] == Nuts and bolts @@ -1893,8 +1901,9 @@ kernel tracer writes to the ring buffer; a * The _LTTng logger_ module. + The LTTng logger module implements the special path:{/proc/lttng-logger} -file so that any executable can generate LTTng events by opening and -writing to this file. +(and path:{/dev/lttng-logger} since LTTng{nbsp}2.11) files so that any +executable can generate LTTng events by opening and writing to those +files. + See <>. @@ -5034,9 +5043,10 @@ variable. === LTTng logger The `lttng-tracer` Linux kernel module, part of -<>, creates the special LTTng logger file -path:{/proc/lttng-logger} when it's loaded. Any application can write -text data to this file to emit an LTTng event. +<>, creates the special LTTng logger files +path:{/proc/lttng-logger} and path:{/dev/lttng-logger} (since +LTTng{nbsp}2.11) when it's loaded. Any application can write text data +to any of those files to emit an LTTng event. [role="img-100"] .An application writes to the LTTng logger file to emit an LTTng event. @@ -5048,7 +5058,7 @@ mostly to instrument shell scripts: [role="term"] ---- -$ echo "Some message, some $variable" > /proc/lttng-logger +$ echo "Some message, some $variable" > /dev/lttng-logger ---- Any event that the LTTng logger emits is named `lttng_logger` and @@ -5060,7 +5070,7 @@ matches its event name, not only the root user or users in the To use the LTTng logger: -* From any application, write text data to the path:{/proc/lttng-logger} +* From any application, write text data to the path:{/dev/lttng-logger} file. The `msg` field of `lttng_logger` event records contains the @@ -5082,9 +5092,9 @@ can be instrumented in a more efficient way, namely: [source,bash] .path:{test.bash} ---- -echo 'Hello, World!' > /proc/lttng-logger +echo 'Hello, World!' > /dev/lttng-logger sleep 2 -df --human-readable --print-type / > /proc/lttng-logger +df --human-readable --print-type / > /dev/lttng-logger ---- <>, -- 2.34.1