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Message-ID: <YrkSkuluNhGcMyOu@debian.me>
Date: Mon, 27 Jun 2022 09:14:42 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Jeff Xie <xiehuan09@...il.com>
Cc: rostedt@...dmis.org, mingo@...hat.com, mhiramat@...nel.org,
zanussi@...nel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, shuah@...nel.org,
linux-doc@...r.kernel.org, corbet@....net, chensong_2000@....cn
Subject: Re: [PATCH v13 4/4] Documentation: trace/objtrace: Add documentation
for objtrace
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.
> +- 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?"
> + 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"?
> + 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):
---- >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
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