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trace doc: convert trace/kprobetrace.txt to rst format

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This converts the plain text documentation to reStructuredText format and
add it into Sphinx TOC tree. No essential content change.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Changbin Du 2018-02-17 13:39:39 +08:00 committed by Jonathan Corbet
parent 1f198e22bc
commit 263ee77574
2 changed files with 53 additions and 44 deletions
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1
Documentation/trace/index.rst
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@ -9,3 +9,4 @@ Linux Tracing Technologies
tracepoint-analysis tracepoint-analysis
ftrace ftrace
ftrace-uses ftrace-uses
kprobetrace

96
Documentation/trace/kprobetrace.txt → Documentation/trace/kprobetrace.rst
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@ -1,8 +1,8 @@
Kprobe-based Event Tracing ==========================
========================== Kprobe-based Event Tracing
==========================
Documentation is written by Masami Hiramatsu
:Author: Masami Hiramatsu
Overview Overview
-------- --------
@ -23,6 +23,8 @@ current_tracer. Instead of that, add probe points via
Synopsis of kprobe_events Synopsis of kprobe_events
------------------------- -------------------------
::
p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
-:[GRP/]EVENT : Clear a probe -:[GRP/]EVENT : Clear a probe
@ -66,7 +68,7 @@ String type is a special type, which fetches a "null-terminated" string from
kernel space. This means it will fail and store NULL if the string container kernel space. This means it will fail and store NULL if the string container
has been paged out. has been paged out.
Bitfield is another special type, which takes 3 parameters, bit-width, bit- Bitfield is another special type, which takes 3 parameters, bit-width, bit-
offset, and container-size (usually 32). The syntax is; offset, and container-size (usually 32). The syntax is::
b<bit-width>@<bit-offset>/<container-size> b<bit-width>@<bit-offset>/<container-size>
@ -75,7 +77,7 @@ For $comm, the default type is "string"; any other type is invalid.
Per-Probe Event Filtering Per-Probe Event Filtering
------------------------- -------------------------
Per-probe event filtering feature allows you to set different filter on each Per-probe event filtering feature allows you to set different filter on each
probe and gives you what arguments will be shown in trace buffer. If an event probe and gives you what arguments will be shown in trace buffer. If an event
name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event
under tracing/events/kprobes/<EVENT>, at the directory you can see 'id', under tracing/events/kprobes/<EVENT>, at the directory you can see 'id',
@ -96,87 +98,93 @@ id:
Event Profiling Event Profiling
--------------- ---------------
You can check the total number of probe hits and probe miss-hits via You can check the total number of probe hits and probe miss-hits via
/sys/kernel/debug/tracing/kprobe_profile. /sys/kernel/debug/tracing/kprobe_profile.
The first column is event name, the second is the number of probe hits, The first column is event name, the second is the number of probe hits,
the third is the number of probe miss-hits. the third is the number of probe miss-hits.
Usage examples Usage examples
-------------- --------------
To add a probe as a new event, write a new definition to kprobe_events To add a probe as a new event, write a new definition to kprobe_events
as below. as below::
echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
This sets a kprobe on the top of do_sys_open() function with recording This sets a kprobe on the top of do_sys_open() function with recording
1st to 4th arguments as "myprobe" event. Note, which register/stack entry is 1st to 4th arguments as "myprobe" event. Note, which register/stack entry is
assigned to each function argument depends on arch-specific ABI. If you unsure assigned to each function argument depends on arch-specific ABI. If you unsure
the ABI, please try to use probe subcommand of perf-tools (you can find it the ABI, please try to use probe subcommand of perf-tools (you can find it
under tools/perf/). under tools/perf/).
As this example shows, users can choose more familiar names for each arguments. As this example shows, users can choose more familiar names for each arguments.
::
echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events
This sets a kretprobe on the return point of do_sys_open() function with This sets a kretprobe on the return point of do_sys_open() function with
recording return value as "myretprobe" event. recording return value as "myretprobe" event.
You can see the format of these events via You can see the format of these events via
/sys/kernel/debug/tracing/events/kprobes/<EVENT>/format. /sys/kernel/debug/tracing/events/kprobes/<EVENT>/format.
::
cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
name: myprobe name: myprobe
ID: 780 ID: 780
format: format:
field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1;signed:0; field:unsigned char common_preempt_count; offset:3; size:1;signed:0;
field:int common_pid; offset:4; size:4; signed:1; field:int common_pid; offset:4; size:4; signed:1;
field:unsigned long __probe_ip; offset:12; size:4; signed:0; field:unsigned long __probe_ip; offset:12; size:4; signed:0;
field:int __probe_nargs; offset:16; size:4; signed:1; field:int __probe_nargs; offset:16; size:4; signed:1;
field:unsigned long dfd; offset:20; size:4; signed:0; field:unsigned long dfd; offset:20; size:4; signed:0;
field:unsigned long filename; offset:24; size:4; signed:0; field:unsigned long filename; offset:24; size:4; signed:0;
field:unsigned long flags; offset:28; size:4; signed:0; field:unsigned long flags; offset:28; size:4; signed:0;
field:unsigned long mode; offset:32; size:4; signed:0; field:unsigned long mode; offset:32; size:4; signed:0;
print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip, print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip,
REC->dfd, REC->filename, REC->flags, REC->mode REC->dfd, REC->filename, REC->flags, REC->mode
You can see that the event has 4 arguments as in the expressions you specified. You can see that the event has 4 arguments as in the expressions you specified.
::
echo > /sys/kernel/debug/tracing/kprobe_events echo > /sys/kernel/debug/tracing/kprobe_events
This clears all probe points. This clears all probe points.
Or, Or,
::
echo -:myprobe >> kprobe_events echo -:myprobe >> kprobe_events
This clears probe points selectively. This clears probe points selectively.
Right after definition, each event is disabled by default. For tracing these Right after definition, each event is disabled by default. For tracing these
events, you need to enable it. events, you need to enable it.
::
echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
And you can see the traced information via /sys/kernel/debug/tracing/trace. And you can see the traced information via /sys/kernel/debug/tracing/trace.
::
cat /sys/kernel/debug/tracing/trace cat /sys/kernel/debug/tracing/trace
# tracer: nop # tracer: nop
# #
# TASK-PID CPU# TIMESTAMP FUNCTION # TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | | # | | | | |
<...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0 <...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0
<...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe <...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe
<...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6 <...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6
<...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 <...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
<...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10 <...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10
<...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 <...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
Each line shows when the kernel hits an event, and <- SYMBOL means kernel Each line shows when the kernel hits an event, and <- SYMBOL means kernel
returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
returns from do_sys_open to sys_open+0x1b). returns from do_sys_open to sys_open+0x1b).