1LIBTRACEEVENT(3) libtraceevent Manual LIBTRACEEVENT(3)
2
6 kbuffer_timestamp, kbuffer_subbuf_timestamp - Functions that read
7 various data of a kbuffer descriptor
8
10 #include <kbuffer.h>
11 unsigned long long kbuffer_timestamp(struct kbuffer *kbuf);
13 unsigned long long kbuffer_subbuf_timestamp(struct kbuffer *kbuf, void *subbuf);
14
16 The function kbuffer_timestamp() returns the timestamp of the current
17 event of kbuf.
18 The function kbuffer_subbuf_timestamp() returns the timestamp for the
20 sub-buffer that was loaded in kbuf. This usually is (but not guaranteed
21 to be) the timestamp of the first event on the sub-buffer.
22 The function kbuffer_start_of_data() returns the offset of where the
24 delta
25
27 kbuffer_read_event() returns the event that the kbuf descriptor is
28 currently at, or NULL if the last event was passed (by
29 kbuffer_next_event()).
30 kbuffer_next_event() returns the next event after the current event or
32 NULL if there are no more events.
33 kbuffer_read_at_offset() returns the event at a given offset from the
35 start of the sub-buffer stored in kbuf, or NULL if there exists no
36 event. Note, offset only needs to be an offset that lands on the
37 record, or is at the start of it. It does not need to be exactly at the
38 beginning of the record.
39 kbuffer_missed_events() returns 0 if there were no missed events before
41 loaded sub-buffer. Returns -1 if there were an unknown number of missed
42 events, or if the number of missed events is known, that number will be
43 returned.
44 kbuffer_event_size() returns the size of the data payload of the
46 current event of kbuf.
47 kbuffer_curr_size() returns the size of the entire record of the
49 current event of kbuf. This includes the size of the meta data for that
50 record.
51 kbuf_curr_offset() returns the offset of the current record from the
53 beginning of the kbuf sub-buffer.
54 kbuf_curr_index() returns the index of the current record from the
56 beginning of the kbuf data section.
57
59 #include <stdio.h>
60 #include <stdlib.h>
61 #include <fcntl.h>
62 #include <unistd.h>
63 #include <sys/stat.h>
64 #include <kbuffer.h>
66 int main (int argc, char **argv)
68 {
69 unsigned long long ts;
70 struct kbuffer *kbuf;
71 struct stat st;
72 char *buf;
73 void *event;
74 int save_offset = -1;
75 int record_size;
76 int offset;
77 int index;
78 int size;
79 int ret;
80 int fd;
81 int i = 0;
82 if (argc < 2) {
84 printf("usage: %s raw-subbuffer-page\n", argv[0]);
85 printf(" Try: dd count=1 bs=4096 if=/sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw of=/tmp/file\n");
86 exit(0);
87 }
88 if (stat(argv[1], &st) < 0) {
90 perror("stat");
91 exit(-1);
92 }
93 buf = malloc(st.st_size);
95 if (!buf) {
96 perror("Allocating buffer");
97 exit(-1);
98 }
99 fd = open(argv[1], O_RDONLY);
101 if (fd < 0) {
102 perror(argv[1]);
103 exit(-1);
104 }
105 ret = read(fd, buf, st.st_size);
107 if (ret < 0) {
108 perror("Reading buffer");
109 exit(-1);
110 }
111 close(fd);
112 kbuf = kbuffer_alloc(KBUFFER_ENDIAN_SAME_AS_HOST,
114 KBUFFER_LSIZE_SAME_AS_HOST);
115 if (!kbuf) {
116 perror("Creating kbuffer");
117 exit(-1);
118 }
119 ret = kbuffer_load_subbuffer(kbuf, buf);
120 if (ret < 0) {
121 perror("Loading sub bufer");
122 exit(-1);
123 }
124 if (kbuffer_subbuffer_size(kbuf) > st.st_size) {
126 fprintf(stderr, "kbuffer is bigger than raw size %d > %ld\n",
127 kbuffer_subbuffer_size(kbuf), st.st_size);
128 exit(-1);
129 }
130 ret = kbuffer_missed_events(kbuf);
132 if (ret) {
133 if (ret > 0)
134 printf("Missed %d events before this buffer\n", ret);
135 else
136 printf("Missed unknown number of events before this buffer\n");
137 }
138 do {
139 event = kbuffer_read_event(kbuf, &ts);
140 if (event) {
141 record_size = kbuffer_curr_size(kbuf);
142 offset = kbuffer_curr_offset(kbuf);
143 index = kbuffer_curr_index(kbuf);
144 size = kbuffer_event_size(kbuf);
145 if (i == 20)
147 save_offset = offset;
148 printf(" event %3d ts:%lld\trecord_size:%d size:%d\tindex:%d offset:%d\n",
149 i++, ts, record_size, size, index, offset);
150 event = kbuffer_next_event(kbuf, NULL);
151 }
152 } while (event);
153 if (!event)
155 printf("Finished sub buffer\n");
156 if (save_offset > 0) {
158 event = kbuffer_read_at_offset(kbuf, save_offset, &ts);
159 if (!event) {
160 fprintf(stderr, "Funny, can't find event 20 at offset %d\n", save_offset);
161 exit(-1);
162 }
163 record_size = kbuffer_curr_size(kbuf);
164 offset = kbuffer_curr_offset(kbuf);
165 index = kbuffer_curr_index(kbuf);
166 size = kbuffer_event_size(kbuf);
167 printf("\n saved event 20 ts:%lld\trecord_size:%d size:%d\tindex:%d offset:%d\n\n",
169 ts, record_size, size, index, offset);
170 }
171 kbuffer_free(kbuf);
172 return 0;
174 }
175
177 event-parse.h
178 Header file to include in order to have access to the library APIs.
179 -ltraceevent
180 Linker switch to add when building a program that uses the library.
181
183 libtraceevent(3), trace-cmd(1)
184
186 Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.
187
189 Report bugs to <linux-trace-devel@vger.kernel.org[2]>
190
192 libtraceevent is Free Software licensed under the GNU LGPL 2.1
193
195 https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/
196
198 1. rostedt@goodmis.org
199 mailto:rostedt@goodmis.org
200 2. linux-trace-devel@vger.kernel.org
202 mailto:linux-trace-devel@vger.kernel.org
203libtraceevent 1.7.2 07/20/2023 LIBTRACEEVENT(3)