docs: add documentation for dm.libdm_log_level

cyphar · corhere · commit 25baee8ab984 · 2024-08-05T17:38:49.000-04:00
This is a new option added specifically to allow for debugging of bugs
in Docker's storage drivers or libdm itself.

Signed-off-by: Aleksa Sarai &lt;asarai@suse.de&gt;
diff --git a/man/dockerd.8.md b/man/dockerd.8.md
@@ -703,6 +703,31 @@ Example use:
 
     $ sudo dockerd --storage-opt dm.xfs_nospace_max_retries=0
 
+##### dm.libdm_log_level
+
+Specifies the maxmimum libdm log level that will be forwarded to the dockerd
+log (as specified by --log-level). This option is primarily intended for
+debugging problems involving libdm. Using values other than the defaults may
+cause false-positive warnings to be logged.
+
+Values specified must fall within the range of valid libdm log levels. At the
+time of writing, the following is the list of libdm log levels as well as their
+corresponding levels when output by dockerd.
+
+| libdm Level | Value | --log-level |
+| ----------- | -----:| ----------- |
+| _LOG_FATAL  |     2 | error       |
+| _LOG_ERR    |     3 | error       |
+| _LOG_WARN   |     4 | warn        |
+| _LOG_NOTICE |     5 | info        |
+| _LOG_INFO   |     6 | info        |
+| _LOG_DEBUG  |     7 | debug       |
+
+Example use:
+
+    $ sudo dockerd \
+	      --log-level debug \
+          --storage-opt dm.libdm_log_level=7
 
 ## ZFS options
 
