Hi Jeff, OK, this looks good to me. Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> And just a note that please add 'Documentation:' tag to the title and Cc to linux-doc@xxxxxxxxxxxxxxx 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@xxxxxxxxx> wrote: > Added documentation explaining how to use objtrace trigger to get the value > of the object. > > Signed-off-by: Jeff Xie <xiehuan09@xxxxxxxxx> > --- > 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@xxxxxxxxxx>
