1 = babeltrace2-source.text.dmesg(7)
2 :manpagetype: component class
3 :revdate: 14 September 2019
8 babeltrace2-source.text.dmesg - Babeltrace 2's Linux kernel ring buffer
14 A Babeltrace~2 compcls:source.text.dmesg message iterator reads the
15 lines of a Linux kernel ring buffer, as printed by the man:dmesg(1)
16 tool, and emits corresponding event messages.
19 Linux kernel ring buffer
20 lines (file or standard input)
25 | out @--> Messages (single stream)
29 include::common-see-babeltrace2-intro.txt[]
31 A compcls:source.text.dmesg message iterator names the events it creates
32 `string`. Each event contain a single payload string field named `str`
33 which contains the corresponding ring buffer line.
35 By default, a compcls:source.text.dmesg message iterator reads the lines
36 of the standard input stream. You can make the message iterator read the
37 lines of a text file instead with the param:path parameter.
39 By default, the message iterator tries to extract the timestamps of the
40 kernel ring buffer lines and use them as the created events's
41 timestamps. A typical man:dmesg(1) line looks like this:
44 [87166.510937] PM: Finishing wakeup.
47 The `[87166.510937]` part is the timestamp to extract. When this
48 information is available, the component creates a clock class which does
49 :not: have the Unix epoch as its origin.
51 You can make the message iterator not extract timestamps from lines with
52 the param:no-extract-timestamp parameter.
56 It is possible that the output of man:dmesg(1) contains unsorted lines,
57 that is, their timestamps go back in time. You can see this with the
58 nlopt:--show-delta option of man:dmesg(1): some time differences can be
61 This is due to a https://lwn.net/Articles/780556/[2019 change] to the
62 kernel's ring buffer API.
64 As of this version, a compcls:source.text.dmesg message iterator
65 requires that the input kernel ring buffer lines be sorted by timestamp
66 (when they have timestamps), failing otherwise.
70 == INITIALIZATION PARAMETERS
72 param:no-extract-timestamp=`yes` vtype:[optional boolean]::
73 Do :not: extract timestamps from the kernel ring buffer lines: set
74 the created event's payload's `str` field to the whole line,
75 including any timestamp prefix.
77 param:path='PATH' vtype:[optional string]::
78 Read the kernel ring buffer lines from the file 'PATH' instead of
79 the standard input stream.
99 include::common-footer.txt[]
104 man:babeltrace2-plugin-text(7),
105 man:babeltrace2-intro(7)