Add documentation explaining how to use objtrace trigger to get the value of the object. Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Bagas Sanjaya <bagasdotme@xxxxxxxxx> Cc: linux-doc@xxxxxxxxxxxxxxx Signed-off-by: Jeff Xie <xiehuan09@xxxxxxxxx> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> --- Changelog: v14: - make documentation more readable and fix literal code block by Bagas Sanjaya Documentation/trace/events.rst | 87 ++++++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst index c47f381d0c00..c15f1d25d4a0 100644 --- a/Documentation/trace/events.rst +++ b/Documentation/trace/events.rst @@ -546,6 +546,93 @@ 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, 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(): + + .. code-block:: c + + 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 as first parameter (arg1) to + to the function: + + .. code-block:: + + # echo 'p bio_add_page arg1=$arg1' > ./kprobe_events + + Secondly, we can get the value dynamically based on the object: + + .. code-block:: + + find the offset of the bi_size in struct bio: + $ gdb vmlinux + (gdb) p &(((struct bio *)0)->bi_iter.bi_size) + $1 = (unsigned int *) 0x28 + + # echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \ + p_bio_add_page_0/trigger + + # cd /sys/kernel/debug/tracing/ + # echo 'p bio_add_page arg1=$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
