[RFC][PATCH v6 0/5] trace: Introduce objtrace trigger to trace the kernel object

[Jeff Xie]

Introduce a method based on function tracer to trace any object and get
the value of the object dynamically. 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 base the 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

The best way to use this is that we can set the entrance event and exit
event, for example, the following example is to set the read_papes as
the entrance event, and set the __blk_account_io_start as the exit event.

# cd /sys/kernel/debug/tracing/
# echo 0 > ./tracing_on
# echo 'p read_pages' >> ./kprobe_events
# echo 'p __blk_account_io_start' >> ./kprobe_events
# echo 'traceon if comm == "cat"' > ./events/kprobes/p_read_pages_0/trigger
# echo 'traceoff if comm == "cat"' > ./events/kprobes/p___blk_account_io_start_0/trigger
# 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: 50/50   #P:1
#
#                                _-----=> irqs-off
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
             cat-95      [000] .....     1.412065: _raw_spin_unlock_irqrestore <-event_triggers_call object:0xffff888108af6328 value:0x0
             cat-95      [000] .....     1.412066: __bio_try_merge_page <-bio_add_page object:0xffff888108af6328 value:0x0
             cat-95      [000] .....     1.412066: __bio_add_page <-bio_add_page object:0xffff888108af6328 value:0x0
             cat-95      [000] .....     1.412066: rcu_read_unlock_strict <-xa_load object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412066: bio_add_page <-ext4_mpage_readpages object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412066: kprobe_ftrace_handler <-ftrace_ops_list_func object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412067: get_kprobe <-kprobe_ftrace_handler object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412067: __bio_try_merge_page <-bio_add_page object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412067: __bio_add_page <-bio_add_page object:0xffff888108af6328 value:0x1000
             cat-95      [000] .....     1.412067: rcu_read_unlock_strict <-xa_load object:0xffff888108af6328 value:0x2000
             cat-95      [000] .....     1.412067: bio_add_page <-ext4_mpage_readpages object:0xffff888108af6328 value:0x2000
             cat-95      [000] .....     1.412067: kprobe_ftrace_handler <-ftrace_ops_list_func object:0xffff888108af6328 value:0x2000
             cat-95      [000] .....     1.412067: get_kprobe <-kprobe_ftrace_handler object:0xffff888108af6328 value:0x2000
             cat-95      [000] .....     1.412067: __bio_try_merge_page <-bio_add_page object:0xffff888108af6328 value:0x2000
             cat-95      [000] .....     1.412068: submit_bio <-ext4_mpage_readpages object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: submit_bio_noacct <-ext4_mpage_readpages object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: __submit_bio <-submit_bio_noacct object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: blk_try_enter_queue <-__submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: rcu_read_unlock_strict <-blk_try_enter_queue object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: rcu_read_unlock_strict <-blk_try_enter_queue object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: submit_bio_checks <-__submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: __cond_resched <-submit_bio_checks object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: rcu_all_qs <-__cond_resched object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412068: should_fail_bio <-submit_bio_checks object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: create_task_io_context <-submit_bio_checks object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: kmem_cache_alloc_node <-create_task_io_context object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: should_failslab <-kmem_cache_alloc_node object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: _raw_spin_lock <-create_task_io_context object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: blk_mq_submit_bio <-__submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: __blk_queue_split <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: bvec_split_segs <-__blk_queue_split object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412069: blk_attempt_plug_merge <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: __blk_mq_sched_bio_merge <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: dd_bio_merge <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: _raw_spin_lock <-dd_bio_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: blk_mq_sched_try_merge <-dd_bio_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: elv_merge <-blk_mq_sched_try_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: elv_rqhash_find <-elv_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: dd_request_merge <-blk_mq_sched_try_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: elv_rb_find <-dd_request_merge object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412070: __blk_mq_alloc_request <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: dd_limit_depth <-__blk_mq_alloc_request object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: blk_mq_get_tag <-__blk_mq_alloc_request object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: __blk_mq_get_tag <-blk_mq_get_tag object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: blk_mq_rq_ctx_init.isra.0 <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: ktime_get <-blk_mq_rq_ctx_init.isra.0 object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: dd_prepare_request <-blk_mq_rq_ctx_init.isra.0 object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: __blk_account_io_start <-blk_mq_submit_bio object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: kprobe_ftrace_handler <-ftrace_ops_list_func object:0xffff888108af6328 value:0x3000
             cat-95      [000] .....     1.412071: get_kprobe <-kprobe_ftrace_handler object:0xffff888108af6328 value:0x3000

Jeff Xie (5):
  trace: Add trace any kernel object
  trace/objtrace: get the value of the object
  trace/README: Document objtrace trigger syntax
  trace/objtrace: Add testcases for objtrace
  trace/objtrace: Add documentation for objtrace

 Documentation/trace/events.rst                | 114 +++
 include/linux/trace_events.h                  |   1 +
 kernel/trace/Kconfig                          |  10 +
 kernel/trace/Makefile                         |   1 +
 kernel/trace/trace.c                          |   3 +
 kernel/trace/trace.h                          |   8 +
 kernel/trace/trace_entries.h                  |  18 +
 kernel/trace/trace_events_trigger.c           |   1 +
 kernel/trace/trace_object.c                   | 660 ++++++++++++++++++
 kernel/trace/trace_output.c                   |  40 ++
 .../ftrace/test.d/trigger/trigger-objtrace.tc |  39 ++
 11 files changed, 895 insertions(+)
 create mode 100644 kernel/trace/trace_object.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-objtrace.tc

-- 
2.25.1