liblog: document the liblog<->logd protocol format
This protocol documentation is spread out among various functions
where it is implemented. This change makes a single
README.protocol.md file with a high level overview, referencing the
struct names where useful.
Test: n/a
Change-Id: I83c9f484352b489b4a20cce241d92413f780f9ec
diff --git a/liblog/README.protocol.md b/liblog/README.protocol.md
new file mode 100644
index 0000000..fef29c9
--- /dev/null
+++ b/liblog/README.protocol.md
@@ -0,0 +1,49 @@
+# liblog -> logd
+
+The data that liblog sends to logd is represented below.
+
+ struct {
+ android_log_header_t header;
+ union {
+ struct {
+ char prio;
+ char tag[...];
+ char message[...];
+ } string;
+ struct {
+ android_event_header_t event_header;
+ android_event_*_t payload[...];
+ } binary;
+ };
+ };
+
+The payload, excluding the header, has a max size of LOGGER_ENTRY_MAX_PAYLOAD.
+
+## header
+
+The header is added immediately before sending the log message to logd.
+
+## `string` payload
+
+The `string` part of the union is for normal buffers (main, system, radio, etc) and consists of a
+single character priority, followed by a variable length null terminated string for the tag, and
+finally a variable length null terminated string for the message.
+
+This payload is used for the `__android_log_buf_write()` family of functions.
+
+## `binary` payload
+
+The `binary` part of the union is for binary buffers (events, security, etc) and consists of an
+android_event_header_t struct followed by a variable number of android_event_*_t
+(android_event_list_t, android_event_int_t, etc) structs.
+
+If multiple android_event_*_t elements are present, then they must be in a list and the first
+element in payload must be an android_event_list_t.
+
+This payload is used for the `__android_log_bwrite()` family of functions. It is additionally used
+for `android_log_write_list()` and the related functions that manipulate event lists.
+
+# logd -> liblog
+
+logd sends a `logger_entry` struct to liblog followed by the payload. The payload is identical to
+the payloads defined above. The max size of the entire message from logd is LOGGER_ENTRY_MAX_LEN.
diff --git a/liblog/logd_writer.cpp b/liblog/logd_writer.cpp
index 06a2baf..a22c3be 100644
--- a/liblog/logd_writer.cpp
+++ b/liblog/logd_writer.cpp
@@ -148,24 +148,6 @@
return 0;
}
- /*
- * struct {
- * // what we provide to socket
- * android_log_header_t header;
- * // caller provides
- * union {
- * struct {
- * char prio;
- * char payload[];
- * } string;
- * struct {
- * uint32_t tag
- * char payload[];
- * } binary;
- * };
- * };
- */
-
header.tid = gettid();
header.realtime.tv_sec = ts->tv_sec;
header.realtime.tv_nsec = ts->tv_nsec;