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Date: Tue, 28 Jun 2022 09:37:17 +0800
From: Jeff Xie <xiehuan09@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
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>,
Bagas Sanjaya <bagasdotme@...il.com>
Subject: Re: [PATCH v13 4/4] Documentation: trace/objtrace: Add documentation
for objtrace
Hi Masami,
I would like to ask if I change the document like "Bagas Sanjaya"
rewording in the next version.
I don't know if I can add your Reviewed-by again, I don't know the
rules very well ;-)
On Mon, Jun 27, 2022 at 3:45 PM Jeff Xie <xiehuan09@...il.com> wrote:
>
> 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
Thanks,
JeffXie
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