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

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
View File

@ -9,3 +9,4 @@ Linux Tracing Technologies
tracepoint-analysis
ftrace
ftrace-uses
kprobetrace

96
Documentation/trace/kprobetrace.txt → Documentation/trace/kprobetrace.rst
View File

@ -1,8 +1,8 @@
Kprobe-based Event Tracing
==========================
Documentation is written by Masami Hiramatsu
==========================
Kprobe-based Event Tracing
==========================
:Author: Masami Hiramatsu
Overview
--------
@ -23,6 +23,8 @@ current_tracer. Instead of that, add probe points via
Synopsis of kprobe_events
-------------------------
::
p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return 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
has been paged out.
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>
@ -75,7 +77,7 @@ For $comm, the default type is "string"; any other type is invalid.
Per-Probe Event Filtering
-------------------------
Per-probe event filtering feature allows you to set different filter on each
Per-probe event filtering feature allows you to set different filter on each
probe and gives you what arguments will be shown in trace buffer. If an event
name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event
under tracing/events/kprobes/<EVENT>, at the directory you can see 'id',
@ -96,87 +98,93 @@ id:
Event Profiling
---------------
You can check the total number of probe hits and probe miss-hits via
You can check the total number of probe hits and probe miss-hits via
/sys/kernel/debug/tracing/kprobe_profile.
The first column is event name, the second is the number of probe hits,
The first column is event name, the second is the number of probe hits,
the third is the number of probe miss-hits.
Usage examples
--------------
To add a probe as a new event, write a new definition to kprobe_events
as below.
as below::
echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
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
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
under tools/perf/).
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
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.
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.
::
cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
name: myprobe
ID: 780
format:
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_preempt_count; offset:3; size:1;signed:0;
field:int common_pid; offset:4; size:4; signed:1;
name: myprobe
ID: 780
format:
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_preempt_count; offset:3; size:1;signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:unsigned long __probe_ip; offset:12; size:4; signed:0;
field:int __probe_nargs; offset:16; size:4; signed:1;
field:unsigned long dfd; offset:20; 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 mode; offset:32; 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:unsigned long dfd; offset:20; 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 mode; offset:32; size:4; signed:0;
print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip,
REC->dfd, REC->filename, REC->flags, REC->mode
print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip,
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
This clears all probe points.
This clears all probe points.
Or,
Or,
::
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.
::
echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/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
# tracer: nop
#
# 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] 1038282.286878: 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] 1038282.286915: 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] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
# tracer: nop
#
# 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] 1038282.286878: 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] 1038282.286915: 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] 1038282.286976: 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 do_sys_open to sys_open+0x1b).