[RFC PATCH v4 00/22] tracing: bootconfig: Boot-time tracing and Extra boot config

Masami Hiramatsu
2019-12-02T10:13:26Z

Hello,

This is the 4th version of the series for the boot-time tracing.

Previous version is here.

https://lkml.kernel.org/r/156678933823.21459.4100380582025186209.stgit@devnote2

After submitted the previous one, I had a talk on Plumbers
tracing track, and got positive feedbacks (Thanks everyone!)
and some concerns about bootloader modification to load
an SKC file.

I got many ideas from the discussion instead of passing
configuration file via bootloader. It seems most feasible way
is embedding the SKC in vmlinux or initrd.

In this version, I renamed the SKC to "extra boot config" so that
user can easier understand what it does. And I changed it to load
with the initrd image.

I also tried to integrate a part of configs into current
kernel command line. With this change, we can write long
options for subsystems, module and systemd into the boot config.
(we maybe possible to set sysctl default value via boot config,
but it's another story.)

This series can be applied on Steve's tracing tree (ftrace/core)
or directly available at;

https://github.com/mhiramat/linux.git ftrace-boottrace-v4

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,

feature.option.foo = 1
feature.option.bar = 2

can be also written in

feature.option {
foo = 1
bar = 2
}

or more compact,

feature.option{foo=1;bar=2}

(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

Usage
=====

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"
enable
}
kprobes.vfs_read {
probes = "vfs_read $arg1 $arg2"
filter = "common_pid < 200"
enable
}
synthetic.initcall_latency {
fields = "unsigned long func", "u64 lat"
actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
}
initcall.initcall_start {
actions = "hist:keys=func:ts0=common_timestamp.usecs"
}
initcall.initcall_finish {
actions = "hist:keys=func:lat=common_timestamp.usecs-$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:*";
tp-printk;
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
==========

- 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

Documentation/admin-guide/bootconfig.rst | 176 ++++++
Documentation/admin-guide/index.rst | 1
Documentation/trace/boottime-trace.rst | 184 ++++++
Documentation/trace/index.rst | 1
MAINTAINERS | 9
fs/proc/Makefile | 1
fs/proc/bootconfig.c | 89 +++
include/linux/bootconfig.h | 221 +++++++
include/linux/trace_events.h | 1
init/Kconfig | 12
init/main.c | 213 ++++++-
kernel/trace/Kconfig | 9
kernel/trace/Makefile | 1
kernel/trace/trace.c | 63 +-
kernel/trace/trace_boot.c | 353 +++++++++++
kernel/trace/trace_events.c | 1
kernel/trace/trace_events_hist.c | 14
kernel/trace/trace_events_trigger.c | 2
kernel/trace/trace_kprobe.c | 81 ++-
lib/Kconfig | 3
lib/Makefile | 2
lib/bootconfig.c | 783 +++++++++++++++++++++++++
tools/Makefile | 11
tools/bootconfig/.gitignore | 1
tools/bootconfig/Makefile | 25 +
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-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-spaceword.bconf | 2
tools/bootconfig/samples/bad-tree.bconf | 5
tools/bootconfig/samples/bad-value.bconf | 3
tools/bootconfig/samples/good-simple.bconf | 11
tools/bootconfig/samples/good-single.bconf | 4
tools/bootconfig/samples/good-tree.bconf | 15
tools/bootconfig/test-bootconfig.sh | 80 +++
46 files changed, 2742 insertions(+), 79 deletions(-)
create mode 100644 Documentation/admin-guide/bootconfig.rst
create mode 100644 Documentation/trace/boottime-trace.rst
create mode 100644 fs/proc/bootconfig.c
create mode 100644 include/linux/bootconfig.h
create mode 100644 kernel/trace/trace_boot.c
create mode 100644 lib/bootconfig.c
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-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-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/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/test-bootconfig.sh

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>