Document filter (help and manpage)

[lttng-tools.git] / src / bin / lttng / commands / enable_events.c

diff --git a/src/bin/lttng/commands/enable_events.c b/src/bin/lttng/commands/enable_events.c
index 3f304a0902ad398bfddacc76ba97ca6595836685..45354573207cc9995106d5862e01e106526eccd1 100644 (file)
--- a/src/bin/lttng/commands/enable_events.c
+++ b/src/bin/lttng/commands/enable_events.c
@@ -168,6 +168,26 @@ static void usage(FILE *ofp)
        fprintf(ofp, "    --filter \'expression\'\n");
        fprintf(ofp, "                           Filter expression on event fields,\n");
        fprintf(ofp, "                           event recording depends on evaluation.\n");
+       fprintf(ofp, "                           Only specify on first activation of\n");
+       fprintf(ofp, "                           a given event within a session.\n");
+       fprintf(ofp, "                           Filter only allowed when enabling\n");
+       fprintf(ofp, "                           events within a session before tracing\n");
+       fprintf(ofp, "                           is started. If the filter fails to link\n");
+       fprintf(ofp, "                           with the event within the traced domain,\n");
+       fprintf(ofp, "                           the event will be discarded. Currently,\n");
+       fprintf(ofp, "                           filter is only implemented for the user-space\n");
+       fprintf(ofp, "                           tracer.\n");
+       fprintf(ofp, "                           Expression examples:.\n");
+       fprintf(ofp, "                           \n");
+       fprintf(ofp, "                           'intfield > 500 && intfield < 503'\n");
+       fprintf(ofp, "                           '(stringfield == \"test\" || intfield != 10) && intfield > 33'\n");
+       fprintf(ofp, "                           'doublefield > 1.1 && intfield < 5.3'\n");
+       fprintf(ofp, "                           \n");
+       fprintf(ofp, "                           Wildcards are allowed at the end of strings:\n");
+       fprintf(ofp, "                           'seqfield1 == \"te*\"'\n");
+       fprintf(ofp, "                           In string literals, the escape character is '\\'.\n");
+       fprintf(ofp, "                           Use '\\*' for the '*' character, and '\\\\' for\n");
+       fprintf(ofp, "                           the '\\' character.\n");
        fprintf(ofp, "\n");
 }