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Date: Sun, 26 Jun 2022 01:10:06 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jeff Xie <xiehuan09@...il.com>
Cc: rostedt@...dmis.org, mingo@...hat.com, mhiramat@...nel.org,
zanussi@...nel.org, linux-kernel@...r.kernel.org,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v12 4/4] trace/objtrace: Add documentation for objtrace
Hi Jeff,
OK, this looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
And just a note that please add 'Documentation:' tag to the title
and Cc to linux-doc@...r.kernel.org and Jonathan Corbet too since
this is a patch for the Documentation/*.
Thank you,
On Tue, 7 Jun 2022 00:09:43 +0800
Jeff Xie <xiehuan09@...il.com> wrote:
> Added documentation explaining how to use objtrace trigger to get the value
> of the object.
>
> Signed-off-by: Jeff Xie <xiehuan09@...il.com>
> ---
> Documentation/trace/events.rst | 83 ++++++++++++++++++++++++++++++++++
> 1 file changed, 83 insertions(+)
>
> diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst
> index c47f381d0c00..0dc475160133 100644
> --- a/Documentation/trace/events.rst
> +++ b/Documentation/trace/events.rst
> @@ -546,6 +546,89 @@ The following commands are supported:
>
> See Documentation/trace/histogram.rst for details and examples.
>
> +- objtrace
> +
> + This command provides a way to get the value of any object, The object
> + can be obtained from the dynamic event(kprobe_event/uprobe_event) or the
> + static event(tracepoint).
> +
> + Usage:
> + When using the kprobe event, only need to set the objtrace(a new trigger),
> + we can get the value of the object. The object is from the setting of the
> + kprobe event.
> +
> + For example:
> + For the function bio_add_page():
> +
> + int bio_add_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int offset)
> +
> + Firstly, we can set the base of the object, thus the first string "arg1"
> + stands for the value of the first parameter of this function bio_add_gage(),
> +
> + # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> +
> + Secondly, we can get the value dynamically based on above object.
> +
> + find the offset of the bi_size in struct bio:
> + $ gdb vmlinux
> + (gdb) p &(((struct bio *)0)->bi_iter.bi_size)
> + $1 = (unsigned int *) 0x28
> +
> + # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \
> + p_bio_add_page_0/trigger
> +
> + # cd /sys/kernel/debug/tracing/
> + # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> + # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/p_bio_add_page_0/trigger
> +
> + # du -sh /test.txt
> + 12.0K /test.txt
> +
> + # cat /test.txt > /dev/null
> + # cat ./trace
> + # tracer: nop
> + #
> + # entries-in-buffer/entries-written: 128/128 #P:4
> + #
> + # _-----=> irqs-off/BH-disabled
> + # / _----=> need-resched
> + # | / _---=> hardirq/softirq
> + # || / _--=> preempt-depth
> + # ||| / _-=> migrate-disable
> + # |||| / delay
> + # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> + # | | | ||||| | |
> + cat-117 [002] ...1. 1.602243: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x0
> + cat-117 [002] ...1. 1.602244: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x0
> + cat-117 [002] ...2. 1.602244: bio_add_page <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x1000
> + cat-117 [002] ...1. 1.602245: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x1000
> + cat-117 [002] ...1. 1.602245: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x1000
> + cat-117 [002] ...2. 1.602245: bio_add_page <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x2000
> + cat-117 [002] ...1. 1.602245: __bio_try_merge_page <-bio_add_page object:0xffff88811bee4000 value:0x2000
> + cat-117 [002] ...1. 1.602245: __bio_add_page <-bio_add_page object:0xffff88811bee4000 value:0x2000
> + cat-117 [002] ...1. 1.602245: submit_bio <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602245: submit_bio_noacct <-ext4_mpage_readpages object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: __submit_bio <-submit_bio_noacct object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: submit_bio_checks <-__submit_bio object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: __cond_resched <-submit_bio_checks object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: should_fail_bio <-submit_bio_checks object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: blk_mq_submit_bio <-submit_bio_noacct object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: blk_attempt_plug_merge <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602246: blk_mq_sched_bio_merge <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602247: __rcu_read_lock <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602247: __rcu_read_unlock <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
> + cat-117 [002] ...1. 1.602247: __blk_mq_alloc_requests <-blk_mq_submit_bio object:0xffff88811bee4000 value:0x3000
> + <idle>-0 [002] d..3. 1.602298: bio_endio <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602298: mpage_end_io <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602298: __read_end_io <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602300: bio_put <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602300: bio_free <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602300: mempool_free <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602300: mempool_free_slab <-blk_update_request object:0xffff88811bee4000 value:0x0
> + <idle>-0 [002] d..3. 1.602300: kmem_cache_free <-blk_update_request object:0xffff88811bee4000 value:0x0
> + ...
> +
> 7. In-kernel trace event API
> ============================
>
> --
> 2.25.1
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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