Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 7 Jul 2023 11:02:10 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> /* Print type function for string type */
> int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent)
> {
>         int len = *(u32 *)data >> 16;
> 
>         if (!len)
>                 trace_seq_puts(s, "(fault)");
>         else
> ----
> 
> In this case, what we need is to set data_loc length = 0 if ret < 0.
> 
> Do you really need to get '"(fault)"' (with double quotation) or
> just '(fault)' (no double quotation) is OK?

 ># echo 'e:myopen syscalls/sys_enter_openat file=+0($filename):ustring' >> /sys/kernel/tracing/dynamic_events
 ># trace-cmd start -e myopen
 ># trace-cmd show
# tracer: nop
#
# entries-in-buffer/entries-written: 19/19   #P:4
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
       trace-cmd-4688    [000] ...1. 466968.015784: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015816: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015833: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015849: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015864: myopen: (syscalls.sys_enter_openat) file=(fault)
       trace-cmd-4688    [000] ...1. 466968.015879: myopen: (syscalls.sys_enter_openat) file=(fault)


Does that answer your question? ;-)

-- Steve