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Subject[PATCH v5 00/22] tracing: bootconfig: Boot-time tracing and Extra boot config

This is the 5th version of the series for the boot-time tracing.

Previous version is here.

In this version, I removed RFC tag from the series.
Changes from the v4 are here, updating bootconfig things.

- [1/22] Fix help comment and indent of Kconfig.
Restrict available characters in values(*)
Drop backslash escape from quoted value(**)
- [3/22] Fix Makefile to compile tool correctly
Remove unused pattern from Makefile
- [4/22] Show test target bootconfig
Add printable value testcases
Add bad array testcase
- [9/22] Fix TOC list
Add notes about available characters.
Fix to use correct quotes (``) for .rst.

(*) this is for preventing admin from shoot himself.
(**) this rule is from legacy command line.

Boot-time tracing features are not modified. I know Tom is working
on exporting synthetic event (and dynamic events) APIs for module.
If that APIs are merged first, I will update my series on top
of that.

This series can be applied on v5.5-rc3 or directly available at; ftrace-boottrace-v5

Extra Boot Config

Extra boot config allows admin to pass a tree-structured key-value
list when booting up the kernel. This expands the kernel command
line in an efficient way.

Each key is described as a dot-jointed-words. And user can write
the key-words in tree stlye. (In this version, the tailing ';'
becomes optional. See Documentation/admin-guide/bootconfig.rst)

For example, = 1 = 2

can be also written in

feature.option {
foo = 1
bar = 2

or more compact,


(Note that in both style, the same words are merged automatically
and make a single tree)
All values are treated as a string, or array of strings, e.g.

feature.options = "foo", "bar"

User can see the loaded key-value list via /proc/bootconfig.
The size is limited upto 32KB and 1024 key-words and values
in total.

Boot with a Boot Config

This version doesn't require to modify boot loaders anymore.
The boot config is loaded with initrd, and there is new "bootconfig"
command under tools/bootconfig.
To add (append) a bootconfig file to an initrd, you can use the
bootconfig command like:

# tools/bootconfig/bootconfig -a your-config /boot/initrd.img-X.Y.Z

This verifies the configuration file too.

Boot-time Tracing

Boot-time tracing supports following boot configs. Please read
Documentation/trace/boottime-trace.rst for details.

- kernel.dump_on_oops [= MODE]
- kernel.traceoff_on_warning
- kernel.tp_printk
- kernel.fgraph_filters = FILTER[, FILTER2...]
- kernel.fgraph_notraces = FILTER[, FILTER2...]
- kernel.fgraph_max_depth = MAX_DEPTH
- ftrace.[instance.INSTANCE.]options = OPT1[,OPT2...]
- ftrace.[instance.INSTANCE.]trace_clock = CLOCK
- ftrace.[instance.INSTANCE.]buffer_size = SIZE
- ftrace.[instance.INSTANCE.]alloc_snapshot
- ftrace.[instance.INSTANCE.]cpumask = CPUMASK
- ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2...]
- ftrace.[instance.INSTANCE.]tracer = TRACER
- ftrace.[instance.INSTANCE.]ftrace.filters
- ftrace.[instance.INSTANCE.]ftrace.notraces
- ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER
- ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2...]
- ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable
- ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2...]
- ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2...]

Kernel and Init Command Line

Boot config also supports kernel and init command line parameters
except for early kernel parameters.

In boot config, all key-values start with "kernel." are automatically
merged into user passed boot command line, and key-values which
start with "init." are also passed to init. These options are visible
on /proc/cmdline.

For example,

kernel {
audit = on
audit_backlog_limit = 256
init.systemd.unified_cgroup_hierarchy = 1


With this series, we can setup new kprobe and synthetic events, more
complicated event filters and trigger actions including histogram
via supplemental kernel cmdline.

We can add filter and actions for each event, define kprobe events,
and synthetic events with histogram like below.

ftrace.event {
task.task_newtask {
filter = "pid < 128"
kprobes.vfs_read {
probes = "vfs_read $arg1 $arg2"
filter = "common_pid < 200"
synthetic.initcall_latency {
fields = "unsigned long func", "u64 lat"
actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
initcall.initcall_start {
actions = "hist:keys=func:ts0=common_timestamp.usecs"
initcall.initcall_finish {
actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"

Also, this supports "instance" node, which allows us to run several
tracers for different purpose at once. For example, one tracer is for
tracing functions start with "user_", and others tracing "kernel_",
you can write boot config as:

ftrace.instance {
foo {
tracer = "function"
ftrace-filters = "user_*"
bar {
tracer = "function"
ftrace-filters = "function_*"

The instance node also accepts event nodes so that each instance
can customize its event tracing.

This boot-time trace also supports ftrace kernel parameters.
For example, following kernel parameters

trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*"

it can be written in boot config like below.

ftrace {
options = sym-addr;
events = "initcall:*";
buffer-size = 1MB;
ftrace-filters = "vfs*";

However, since the initialization timing is different, if you need
to trace very early boot, please use normal kernel parameters.

Some Notes

- To align the legacy command line rule, I made the quotes (double
quotes or single quotes) not able to be escaped.
Also, this rejects non-printable chars (except for space). Actually
legacy cmdline accepts any of them, but it might confuse users if
they put a control code by mistake. Imagine that they put a "\b"
on it...

- Since it is not easy to write boot-time tracing without any bug
in bootconfig, a user-helper command will be needed.
That command will generate a boot config file from current ftrace
settings, or try to apply given boot config setting to the ftrace.

- It is also possible to embed boot config file into the kernel
image for the environment which doesn't use initrd. But in that
case, user can not update the boot config.

- As you can see, the EVENT.actions value is a bit ugly since histogram
interface settings are bit complicated. Maybe we can introduce more
abstractive syntax for that. e.g.

ftrace.event.synthetic.initcall_latency {
fields = "unsigned long func", "u64 lat"
hist {
from {
event = initcall.initcall_start
key = func
assigns = "ts0=common_timestamp.usecs"
to {
event = initcall.initcall_finish
key = func
assigns = "lat=common_timestamp.usecs-$ts0"
onmatch = func, $lat
keys = func.sym, lat
vals = lat
sort = lat

Any suggestions, thoughts?

Thank you,


Masami Hiramatsu (22):
bootconfig: Add Extra Boot Config support
bootconfig: Load boot config from the tail of initrd
tools: bootconfig: Add bootconfig command
tools: bootconfig: Add bootconfig test script
proc: bootconfig: Add /proc/bootconfig to show boot config list
init/main.c: Alloc initcall_command_line in do_initcall() and free it
bootconfig: init: Allow admin to use bootconfig for kernel command line
bootconfig: init: Allow admin to use bootconfig for init command line
Documentation: bootconfig: Add a doc for extended boot config
tracing: Apply soft-disabled and filter to tracepoints printk
tracing: kprobes: Output kprobe event to printk buffer
tracing: kprobes: Register to dynevent earlier stage
tracing: Accept different type for synthetic event fields
tracing: Add NULL trace-array check in print_synth_event()
tracing/boot: Add boot-time tracing
tracing/boot: Add per-event settings
tracing/boot Add kprobe event support
tracing/boot: Add synthetic event support
tracing/boot: Add instance node support
tracing/boot: Add cpu_mask option support
tracing/boot: Add function tracer filter options
Documentation: tracing: Add boot-time tracing document

tools/bootconfig/.gitignore | 1
tools/bootconfig/Makefile | 23 ++
tools/bootconfig/include/linux/bootconfig.h | 7
tools/bootconfig/include/linux/bug.h | 12 +
tools/bootconfig/include/linux/ctype.h | 7
tools/bootconfig/include/linux/errno.h | 7
tools/bootconfig/include/linux/kernel.h | 18 +
tools/bootconfig/include/linux/printk.h | 13 +
tools/bootconfig/include/linux/string.h | 32 ++
tools/bootconfig/main.c | 337 +++++++++++++++++++++++
tools/bootconfig/samples/bad-array.bconf | 2
tools/bootconfig/samples/bad-dotword.bconf | 4
tools/bootconfig/samples/bad-empty.bconf | 1
tools/bootconfig/samples/bad-keyerror.bconf | 2
tools/bootconfig/samples/bad-longkey.bconf | 1
tools/bootconfig/samples/bad-manywords.bconf | 1
tools/bootconfig/samples/bad-no-keyword.bconf | 2
tools/bootconfig/samples/bad-nonprintable.bconf | 2
tools/bootconfig/samples/bad-spaceword.bconf | 2
tools/bootconfig/samples/bad-tree.bconf | 5
tools/bootconfig/samples/bad-value.bconf | 3
tools/bootconfig/samples/escaped.bconf | 3
tools/bootconfig/samples/good-printables.bconf | 2
tools/bootconfig/samples/good-simple.bconf | 11 +
tools/bootconfig/samples/good-single.bconf | 4
tools/bootconfig/samples/good-tree.bconf | 12 +
tools/bootconfig/ | 80 +++++
27 files changed, 594 insertions(+)
create mode 100644 tools/bootconfig/.gitignore
create mode 100644 tools/bootconfig/Makefile
create mode 100644 tools/bootconfig/include/linux/bootconfig.h
create mode 100644 tools/bootconfig/include/linux/bug.h
create mode 100644 tools/bootconfig/include/linux/ctype.h
create mode 100644 tools/bootconfig/include/linux/errno.h
create mode 100644 tools/bootconfig/include/linux/kernel.h
create mode 100644 tools/bootconfig/include/linux/printk.h
create mode 100644 tools/bootconfig/include/linux/string.h
create mode 100644 tools/bootconfig/main.c
create mode 100644 tools/bootconfig/samples/bad-array.bconf
create mode 100644 tools/bootconfig/samples/bad-dotword.bconf
create mode 100644 tools/bootconfig/samples/bad-empty.bconf
create mode 100644 tools/bootconfig/samples/bad-keyerror.bconf
create mode 100644 tools/bootconfig/samples/bad-longkey.bconf
create mode 100644 tools/bootconfig/samples/bad-manywords.bconf
create mode 100644 tools/bootconfig/samples/bad-no-keyword.bconf
create mode 100644 tools/bootconfig/samples/bad-nonprintable.bconf
create mode 100644 tools/bootconfig/samples/bad-spaceword.bconf
create mode 100644 tools/bootconfig/samples/bad-tree.bconf
create mode 100644 tools/bootconfig/samples/bad-value.bconf
create mode 100644 tools/bootconfig/samples/escaped.bconf
create mode 100644 tools/bootconfig/samples/good-printables.bconf
create mode 100644 tools/bootconfig/samples/good-simple.bconf
create mode 100644 tools/bootconfig/samples/good-single.bconf
create mode 100644 tools/bootconfig/samples/good-tree.bconf
create mode 100755 tools/bootconfig/

Masami Hiramatsu (Linaro) <>

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