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-rw-r--r--samples/trace_events/trace-events-sample.h27
1 files changed, 27 insertions, 0 deletions
diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h
index 13a35f7cbe66..e61471ab7d14 100644
--- a/samples/trace_events/trace-events-sample.h
+++ b/samples/trace_events/trace-events-sample.h
@@ -141,6 +141,33 @@
* In most cases, the __assign_str() macro will take the same
* parameters as the __string() macro had to declare the string.
*
+ * __string_len: This is a helper to a __dynamic_array, but it understands
+ * that the array has characters in it, and with the combined
+ * use of __assign_str_len(), it will allocate 'len' + 1 bytes
+ * in the ring buffer and add a '\0' to the string. This is
+ * useful if the string being saved has no terminating '\0' byte.
+ * It requires that the length of the string is known as it acts
+ * like a memcpy().
+ *
+ * Declared with:
+ *
+ * __string_len(foo, bar, len)
+ *
+ * To assign this string, use the helper macro __assign_str_len().
+ *
+ * __assign_str(foo, bar, len);
+ *
+ * Then len + 1 is allocated to the ring buffer, and a nul terminating
+ * byte is added. This is similar to:
+ *
+ * memcpy(__get_str(foo), bar, len);
+ * __get_str(foo)[len] = 0;
+ *
+ * The advantage of using this over __dynamic_array, is that it
+ * takes care of allocating the extra byte on the ring buffer
+ * for the '\0' terminating byte, and __get_str(foo) can be used
+ * in the TP_printk().
+ *
* __bitmask: This is another kind of __dynamic_array, but it expects
* an array of longs, and the number of bits to parse. It takes
* two parameters (name, nr_bits), where name is the name of the