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1# liblog -> logd
2
3The data that liblog sends to logd is represented below.
4
5    struct {
6        android_log_header_t header;
7        union {
8           struct {
9                char     prio;
10                char     tag[...];
11                char     message[...];
12            } string;
13            struct {
14                android_event_header_t event_header;
15                android_event_*_t      payload[...];
16            } binary;
17        };
18    };
19
20where the embedded structs are defined as:
21
22    struct android_log_header_t {
23        uint8_t id;
24        uint16_t tid;
25        log_time realtime;
26    };
27
28    struct log_time {
29        uint32_t tv_sec = 0;
30        uint32_t tv_nsec = 0;
31    }
32
33    struct android_event_header_t {
34        int32_t tag;
35    };
36
37    struct android_event_list_t {
38        int8_t type;  // EVENT_TYPE_LIST
39        int8_t element_count;
40    };
41
42    struct android_event_float_t {
43        int8_t type;  // EVENT_TYPE_FLOAT
44        float data;
45    };
46
47    struct android_event_int_t {
48        int8_t type;   // EVENT_TYPE_INT
49        int32_t data;
50    } android_event_int_t;
51
52    struct android_event_long_t {
53        int8_t type;   // EVENT_TYPE_LONG
54        int64_t data;
55    };
56
57    struct android_event_string_t {
58        int8_t type;     // EVENT_TYPE_STRING;
59        int32_t length;
60        char data[];
61    };
62
63The payload, excluding the header, has a max size of LOGGER_ENTRY_MAX_PAYLOAD.
64
65## header
66
67The header is added immediately before sending the log message to logd.
68
69## `string` payload
70
71The `string` part of the union is for normal buffers (main, system, radio, etc) and consists of a
72single character priority, followed by a variable length null terminated string for the tag, and
73finally a variable length null terminated string for the message.
74
75This payload is used for the `__android_log_buf_write()` family of functions.
76
77## `binary` payload
78
79The `binary` part of the union is for binary buffers (events, security, etc) and consists of an
80android_event_header_t struct followed by a variable number of android_event_*_t
81(android_event_list_t, android_event_int_t, etc) structs.
82
83If multiple android_event_*_t elements are present, then they must be in a list and the first
84element in payload must be an android_event_list_t.
85
86This payload is used for the `__android_log_bwrite()` family of functions. It is additionally used
87for `android_log_write_list()` and the related functions that manipulate event lists.
88
89# logd -> liblog
90
91logd sends a `logger_entry` struct to liblog followed by the payload. The payload is identical to
92the payloads defined above. The max size of the entire message from logd is LOGGER_ENTRY_MAX_LEN.
93