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Date: Mon, 27 Jun 2022 15:45:39 +0800
From: Jeff Xie <xiehuan09@...il.com>
To: Bagas Sanjaya <bagasdotme@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
Masami Hiramatsu <mhiramat@...nel.org>,
Tom Zanussi <zanussi@...nel.org>, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
Song Chen <chensong_2000@....cn>
Subject: Re: [PATCH v13 4/4] Documentation: trace/objtrace: Add documentation
for objtrace
Hi,
On Mon, Jun 27, 2022 at 10:14 AM Bagas Sanjaya <bagasdotme@...il.com> wrote:
>
> On Sun, Jun 26, 2022 at 10:56:04AM +0800, Jeff Xie wrote:
> > Added documentation explaining how to use objtrace trigger to get the value
> > of the object.
> >
>
> Write "Add documentation..." instead.
Thanks, I will change it.
> > +- 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.
> > +
>
> Did you mean "the object value can be obtained by only needing to set the
> objtrace?"
Yes, that's what it means.
> > + 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
> > +
>
> Did you mean "the first parameter (arg1) is the parameter value of function
> that is passed to kprobe_event, in this case the object base"?
Yes, that's what it means.
> > + 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
> > + ...
> > +
>
> The output is messy, because for code example and output, literal code
> blocks aren't used, hence trigger new warnings:
>
> Documentation/trace/events.rst:564: WARNING: Inline emphasis start-string without end-string.
> Documentation/trace/events.rst:564: WARNING: Inline emphasis start-string without end-string.
> Documentation/trace/events.rst:573: WARNING: Inline emphasis start-string without end-string.
> Documentation/trace/events.rst:573: WARNING: Inline emphasis start-string without end-string.
> Documentation/trace/events.rst:602: WARNING: Unexpected indentation.
> Documentation/trace/events.rst:622: WARNING: Block quote ends without a blank line; unexpected unindent.
> Documentation/trace/events.rst:630: WARNING: Unexpected indentation.
>
> I had to apply the following fixup (with rewording):
Thank you so much for your help, It looks better ;-)
> ---- >8 ----
>
> diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst
> index 0dc47516013331..c15f1d25d4a071 100644
> --- a/Documentation/trace/events.rst
> +++ b/Documentation/trace/events.rst
> @@ -549,85 +549,89 @@ The following commands are supported:
> - 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).
> + 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.
> + When using the kprobe event, by only need to set the objtrace (a new
> + trigger), we can get the value of object that is set by kprobe event.
>
> - For example:
> - For the function bio_add_page():
> + For example, for the function bio_add_page():
>
> - int bio_add_page(struct bio *bio, struct page *page,
> - unsigned int len, unsigned int offset)
> + .. code-block:: c
>
> - 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(),
> + int bio_add_page(struct bio *bio, struct page *page,
> + unsigned int len, unsigned int offset)
>
> - # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> + Firstly, we can set the base of the object as first parameter (arg1) to
> + to the function:
>
> - Secondly, we can get the value dynamically based on above object.
> + .. code-block::
>
> - find the offset of the bi_size in struct bio:
> - $ gdb vmlinux
> - (gdb) p &(((struct bio *)0)->bi_iter.bi_size)
> - $1 = (unsigned int *) 0x28
> + # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
>
> - # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \
> - p_bio_add_page_0/trigger
> + Secondly, we can get the value dynamically based on the object:
>
> - # 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
> + .. code-block::
>
> - # du -sh /test.txt
> - 12.0K /test.txt
> + 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
>
> - # 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
> - ...
> + # 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
> ============================
>
>
> Thanks.
>
> --
> An old man doll... just what I always wanted! - Clara
Thanks,
JeffXie
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