€•É¨      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ%/translations/zh_CN/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/zh_TW/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/it_IT/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ja_JP/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ko_KR/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/sp_SP/trace/fprobetrace”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒcomment”“”)”}”(hŒ SPDX-License-Identifier: GPL-2.0”h]”hŒ SPDX-License-Identifier: GPL-2.0”…””}”hh£sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1h¡hhhžhhŸŒ?/var/lib/git/docbuild/linux/Documentation/trace/fprobetrace.rst”h KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒFprobe-based Event Tracing”h]”hŒFprobe-based Event Tracing”…””}”(hh»hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh¶hžhhŸh³h Kubh¢)”}”(hŒ.Author: Masami Hiramatsu <mhiramat@kernel.org>”h]”hŒ.Author: Masami Hiramatsu <mhiramat@kernel.org>”…””}”hhÉsbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1h¡hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒOverview”h]”hŒOverview”…””}”(hhÚhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh×hžhhŸh³h K
ubhŒ	paragraph”“”)”}”(hŒ¶Fprobe event is similar to the kprobe event, but limited to probe on
the function entry and exit only. It is good enough for many use cases
which only traces some specific functions.”h]”hŒ¶Fprobe event is similar to the kprobe event, but limited to probe on
the function entry and exit only. It is good enough for many use cases
which only traces some specific functions.”…””}”(hhêhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Khh×hžhubhé)”}”(hŒçThis document also covers tracepoint probe events (tprobe) since this
is also works only on the tracepoint entry. User can trace a part of
tracepoint argument, or the tracepoint without trace-event, which is
not exposed on tracefs.”h]”hŒçThis document also covers tracepoint probe events (tprobe) since this
is also works only on the tracepoint entry. User can trace a part of
tracepoint argument, or the tracepoint without trace-event, which is
not exposed on tracefs.”…””}”(hhøhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Khh×hžhubhé)”}”(hŒ†As same as other dynamic events, fprobe events and tracepoint probe
events are defined via `dynamic_events` interface file on tracefs.”h]”(hŒ[As same as other dynamic events, fprobe events and tracepoint probe
events are defined via ”…””}”(hj  hžhhŸNh NubhŒtitle_reference”“”)”}”(hŒ`dynamic_events`”h]”hŒdynamic_events”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hj  ubhŒ interface file on tracefs.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Khh×hžhubeh}”(h]”Œoverview”ah ]”h"]”Œoverview”ah$]”h&]”uh1h´hh¶hžhhŸh³h K
ubhµ)”}”(hhh]”(hº)”}”(hŒSynopsis of fprobe-events”h]”hŒSynopsis of fprobe-events”…””}”(hj3  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj0  hžhhŸh³h KubhŒliteral_block”“”)”}”(hXþ	   f[:[GRP1/][EVENT1]] SYM [FETCHARGS]                       : Probe on function entry
 f[MAXACTIVE][:[GRP1/][EVENT1]] SYM%return [FETCHARGS]     : Probe on function exit
 t[:[GRP2/][EVENT2]] TRACEPOINT [FETCHARGS]                : Probe on tracepoint

GRP1           : Group name for fprobe. If omitted, use "fprobes" for it.
GRP2           : Group name for tprobe. If omitted, use "tracepoints" for it.
EVENT1         : Event name for fprobe. If omitted, the event name is
                 "SYM__entry" or "SYM__exit".
EVENT2         : Event name for tprobe. If omitted, the event name is
                 the same as "TRACEPOINT", but if the "TRACEPOINT" starts
                 with a digit character, "_TRACEPOINT" is used.
MAXACTIVE      : Maximum number of instances of the specified function that
                 can be probed simultaneously, or 0 for the default value
                 as defined in Documentation/trace/fprobe.rst

FETCHARGS      : Arguments. Each probe can have up to 128 args.
 ARG           : Fetch "ARG" function argument using BTF (only for function
                 entry or tracepoint.) (\*1)
 @ADDR         : Fetch memory at ADDR (ADDR should be in kernel)
 @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
 $stackN       : Fetch Nth entry of stack (N >= 0)
 $stack        : Fetch stack address.
 $argN         : Fetch the Nth function argument. (N >= 1) (\*2)
 $retval       : Fetch return value.(\*3)
 $comm         : Fetch current task comm.
 +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*4)(\*5)
 \IMM          : Store an immediate value to the argument.
 NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
 FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
                 (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
                 (x8/x16/x32/x64), "char", "string", "ustring", "symbol", "symstr"
                 and bitfield are supported.

 (\*1) This is available only when BTF is enabled.
 (\*2) only for the probe on function entry (offs == 0). Note, this argument access
       is best effort, because depending on the argument type, it may be passed on
       the stack. But this only support the arguments via registers.
 (\*3) only for return probe. Note that this is also best effort. Depending on the
       return value type, it might be passed via a pair of registers. But this only
       accesses one register.
 (\*4) this is useful for fetching a field of data structures.
 (\*5) "u" means user-space dereference.”h]”hXþ	   f[:[GRP1/][EVENT1]] SYM [FETCHARGS]                       : Probe on function entry
 f[MAXACTIVE][:[GRP1/][EVENT1]] SYM%return [FETCHARGS]     : Probe on function exit
 t[:[GRP2/][EVENT2]] TRACEPOINT [FETCHARGS]                : Probe on tracepoint

GRP1           : Group name for fprobe. If omitted, use "fprobes" for it.
GRP2           : Group name for tprobe. If omitted, use "tracepoints" for it.
EVENT1         : Event name for fprobe. If omitted, the event name is
                 "SYM__entry" or "SYM__exit".
EVENT2         : Event name for tprobe. If omitted, the event name is
                 the same as "TRACEPOINT", but if the "TRACEPOINT" starts
                 with a digit character, "_TRACEPOINT" is used.
MAXACTIVE      : Maximum number of instances of the specified function that
                 can be probed simultaneously, or 0 for the default value
                 as defined in Documentation/trace/fprobe.rst

FETCHARGS      : Arguments. Each probe can have up to 128 args.
 ARG           : Fetch "ARG" function argument using BTF (only for function
                 entry or tracepoint.) (\*1)
 @ADDR         : Fetch memory at ADDR (ADDR should be in kernel)
 @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
 $stackN       : Fetch Nth entry of stack (N >= 0)
 $stack        : Fetch stack address.
 $argN         : Fetch the Nth function argument. (N >= 1) (\*2)
 $retval       : Fetch return value.(\*3)
 $comm         : Fetch current task comm.
 +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*4)(\*5)
 \IMM          : Store an immediate value to the argument.
 NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
 FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
                 (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
                 (x8/x16/x32/x64), "char", "string", "ustring", "symbol", "symstr"
                 and bitfield are supported.

 (\*1) This is available only when BTF is enabled.
 (\*2) only for the probe on function entry (offs == 0). Note, this argument access
       is best effort, because depending on the argument type, it may be passed on
       the stack. But this only support the arguments via registers.
 (\*3) only for return probe. Note that this is also best effort. Depending on the
       return value type, it might be passed via a pair of registers. But this only
       accesses one register.
 (\*4) this is useful for fetching a field of data structures.
 (\*5) "u" means user-space dereference.”…””}”hjC  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h Khj0  hžhubhé)”}”(hŒRFor the details of TYPE, see :ref:`kprobetrace documentation <kprobetrace_types>`.”h]”(hŒFor the details of TYPE, see ”…””}”(hjQ  hžhhŸNh Nubh)”}”(hŒ4:ref:`kprobetrace documentation <kprobetrace_types>`”h]”hŒinline”“”)”}”(hj[  h]”hŒkprobetrace documentation”…””}”(hj_  hžhhŸNh Nubah}”(h]”h ]”(Œxref”Œstd”Œstd-ref”eh"]”h$]”h&]”uh1j]  hjY  ubah}”(h]”h ]”h"]”h$]”h&]”Œrefdoc”Œtrace/fprobetrace”Œ	refdomain”jj  Œreftype”Œref”Œrefexplicit”ˆŒrefwarn”ˆŒ	reftarget”Œkprobetrace_types”uh1hhŸh³h KGhjQ  ubhŒ.”…””}”(hjQ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KGhj0  hžhubeh}”(h]”Œsynopsis-of-fprobe-events”ah ]”h"]”Œsynopsis of fprobe-events”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒFunction arguments at exit”h]”hŒFunction arguments at exit”…””}”(hj“  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj  hžhhŸh³h KJubhé)”}”(hXc  Function arguments can be accessed at exit probe using $arg<N> fetcharg. This
is useful to record the function parameter and return value at once, and
trace the difference of structure fields (for debugging a function whether it
correctly updates the given data structure or not)
See the :ref:`sample<fprobetrace_exit_args_sample>` below for how it works.”h]”(hX   Function arguments can be accessed at exit probe using $arg<N> fetcharg. This
is useful to record the function parameter and return value at once, and
trace the difference of structure fields (for debugging a function whether it
correctly updates the given data structure or not)
See the ”…””}”(hj¡  hžhhŸNh Nubh)”}”(hŒ+:ref:`sample<fprobetrace_exit_args_sample>`”h]”j^  )”}”(hj«  h]”hŒsample”…””}”(hj­  hžhhŸNh Nubah}”(h]”h ]”(ji  Œstd”Œstd-ref”eh"]”h$]”h&]”uh1j]  hj©  ubah}”(h]”h ]”h"]”h$]”h&]”Œrefdoc”jv  Œ	refdomain”j·  Œreftype”Œref”Œrefexplicit”ˆŒrefwarn”ˆj|  Œfprobetrace_exit_args_sample”uh1hhŸh³h KKhj¡  ubhŒ below for how it works.”…””}”(hj¡  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KKhj  hžhubeh}”(h]”Œfunction-arguments-at-exit”ah ]”h"]”Œfunction arguments at exit”ah$]”h&]”uh1h´hh¶hžhhŸh³h KJubhµ)”}”(hhh]”(hº)”}”(hŒBTF arguments”h]”hŒBTF arguments”…””}”(hjÞ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjÛ  hžhhŸh³h KRubhé)”}”(hXR  BTF (BPF Type Format) argument allows user to trace function and tracepoint
parameters by its name instead of ``$argN``. This feature is available if the
kernel is configured with CONFIG_BPF_SYSCALL and CONFIG_DEBUG_INFO_BTF.
If user only specify the BTF argument, the event's argument name is also
automatically set by the given name. ::”h]”(hŒnBTF (BPF Type Format) argument allows user to trace function and tracepoint
parameters by its name instead of ”…””}”(hjì  hžhhŸNh NubhŒliteral”“”)”}”(hŒ	``$argN``”h]”hŒ$argN”…””}”(hjö  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjì  ubhŒÚ. This feature is available if the
kernel is configured with CONFIG_BPF_SYSCALL and CONFIG_DEBUG_INFO_BTF.
If user only specify the BTF argument, the eventâ€™s argument name is also
automatically set by the given name.”…””}”(hjì  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KShjÛ  hžhubjB  )”}”(hŒ{# echo 'f:myprobe vfs_read count pos' >> dynamic_events
# cat dynamic_events
f:fprobes/myprobe vfs_read count=count pos=pos”h]”hŒ{# echo 'f:myprobe vfs_read count pos' >> dynamic_events
# cat dynamic_events
f:fprobes/myprobe vfs_read count=count pos=pos”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KYhjÛ  hžhubhé)”}”(hŒúIt also chooses the fetch type from BTF information. For example, in the above
example, the ``count`` is unsigned long, and the ``pos`` is a pointer. Thus,
both are converted to 64bit unsigned long, but only ``pos`` has "%Lx"
print-format as below ::”h]”(hŒ\It also chooses the fetch type from BTF information. For example, in the above
example, the ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ	``count``”h]”hŒcount”…””}”(hj$  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ is unsigned long, and the ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``pos``”h]”hŒpos”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒI is a pointer. Thus,
both are converted to 64bit unsigned long, but only ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``pos``”h]”hŒpos”…””}”(hjH  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ$ has â€œ%Lxâ€
print-format as below”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h K]hjÛ  hžhubjB  )”}”(hX‘  # cat events/fprobes/myprobe/format
name: myprobe
ID: 1313
format:
       field:unsigned short common_type;       offset:0;       size:2; signed:0;
       field:unsigned char common_flags;       offset:2;       size:1; signed:0;
       field:unsigned char common_preempt_count;       offset:3;       size:1; signed:0;
       field:int common_pid;   offset:4;       size:4; signed:1;

       field:unsigned long __probe_ip; offset:8;       size:8; signed:0;
       field:u64 count;        offset:16;      size:8; signed:0;
       field:u64 pos;  offset:24;      size:8; signed:0;

print fmt: "(%lx) count=%Lu pos=0x%Lx", REC->__probe_ip, REC->count, REC->pos”h]”hX‘  # cat events/fprobes/myprobe/format
name: myprobe
ID: 1313
format:
       field:unsigned short common_type;       offset:0;       size:2; signed:0;
       field:unsigned char common_flags;       offset:2;       size:1; signed:0;
       field:unsigned char common_preempt_count;       offset:3;       size:1; signed:0;
       field:int common_pid;   offset:4;       size:4; signed:1;

       field:unsigned long __probe_ip; offset:8;       size:8; signed:0;
       field:u64 count;        offset:16;      size:8; signed:0;
       field:u64 pos;  offset:24;      size:8; signed:0;

print fmt: "(%lx) count=%Lu pos=0x%Lx", REC->__probe_ip, REC->count, REC->pos”…””}”hj`  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KbhjÛ  hžhubhé)”}”(hŒ›If user unsures the name of arguments, ``$arg*`` will be helpful. The ``$arg*``
is expanded to all function arguments of the function or the tracepoint. ::”h]”(hŒ'If user unsures the name of arguments, ”…””}”(hjn  hžhhŸNh Nubjõ  )”}”(hŒ	``$arg*``”h]”hŒ$arg*”…””}”(hjv  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjn  ubhŒ will be helpful. The ”…””}”(hjn  hžhhŸNh Nubjõ  )”}”(hŒ	``$arg*``”h]”hŒ$arg*”…””}”(hjˆ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjn  ubhŒI
is expanded to all function arguments of the function or the tracepoint.”…””}”(hjn  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KqhjÛ  hžhubjB  )”}”(hŒ‰# echo 'f:myprobe vfs_read $arg*' >> dynamic_events
# cat dynamic_events
f:fprobes/myprobe vfs_read file=file buf=buf count=count pos=pos”h]”hŒ‰# echo 'f:myprobe vfs_read $arg*' >> dynamic_events
# cat dynamic_events
f:fprobes/myprobe vfs_read file=file buf=buf count=count pos=pos”…””}”hj   sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KthjÛ  hžhubhé)”}”(hŒ°BTF also affects the ``$retval``. If user doesn't set any type, the retval
type is automatically picked from the BTF. If the function returns ``void``,
``$retval`` is rejected.”h]”(hŒBTF also affects the ”…””}”(hj®  hžhhŸNh Nubjõ  )”}”(hŒ``$retval``”h]”hŒ$retval”…””}”(hj¶  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj®  ubhŒp. If user doesnâ€™t set any type, the retval
type is automatically picked from the BTF. If the function returns ”…””}”(hj®  hžhhŸNh Nubjõ  )”}”(hŒ``void``”h]”hŒvoid”…””}”(hjÈ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj®  ubhŒ,
”…””}”(hj®  hžhhŸNh Nubjõ  )”}”(hŒ``$retval``”h]”hŒ$retval”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj®  ubhŒ is rejected.”…””}”(hj®  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KxhjÛ  hžhubhé)”}”(hŒ•You can access the data fields of a data structure using allow operator ``->``
(for pointer type) and dot operator ``.`` (for data structure type.)::”h]”(hŒHYou can access the data fields of a data structure using allow operator ”…””}”(hjò  hžhhŸNh Nubjõ  )”}”(hŒ``->``”h]”hŒ->”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjò  ubhŒ%
(for pointer type) and dot operator ”…””}”(hjò  hžhhŸNh Nubjõ  )”}”(hŒ``.``”h]”hŒ.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjò  ubhŒ (for data structure type.):”…””}”(hjò  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h K|hjÛ  hžhubjB  )”}”(hŒW# echo 't sched_switch preempt prev_pid=prev->pid next_pid=next->pid' >> dynamic_events”h]”hŒW# echo 't sched_switch preempt prev_pid=prev->pid next_pid=next->pid' >> dynamic_events”…””}”hj$  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KhjÛ  hžhubhé)”}”(hX  The field access operators, ``->`` and ``.`` can be combined for accessing deeper
members and other structure members pointed by the member. e.g. ``foo->bar.baz->qux``
If there is non-name union member, you can directly access it as the C code does.
For example::”h]”(hŒThe field access operators, ”…””}”(hj2  hžhhŸNh Nubjõ  )”}”(hŒ``->``”h]”hŒ->”…””}”(hj:  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj2  ubhŒ and ”…””}”(hj2  hžhhŸNh Nubjõ  )”}”(hŒ``.``”h]”hŒ.”…””}”(hjL  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj2  ubhŒf can be combined for accessing deeper
members and other structure members pointed by the member. e.g. ”…””}”(hj2  hžhhŸNh Nubjõ  )”}”(hŒ``foo->bar.baz->qux``”h]”hŒfoo->bar.baz->qux”…””}”(hj^  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj2  ubhŒ_
If there is non-name union member, you can directly access it as the C code does.
For example:”…””}”(hj2  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KhjÛ  hžhubjB  )”}”(hŒEstruct {
       union {
       int a;
       int b;
       };
} *foo;”h]”hŒEstruct {
       union {
       int a;
       int b;
       };
} *foo;”…””}”hjv  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h K†hjÛ  hžhubhé)”}”(hŒFTo access ``a`` and ``b``, use ``foo->a`` and ``foo->b`` in this case.”h]”(hŒ
To access ”…””}”(hj„  hžhhŸNh Nubjõ  )”}”(hŒ``a``”h]”hŒa”…””}”(hjŒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj„  ubhŒ and ”…””}”(hj„  hžhhŸNh Nubjõ  )”}”(hŒ``b``”h]”hŒb”…””}”(hjž  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj„  ubhŒ, use ”…””}”(hj„  hžhhŸNh Nubjõ  )”}”(hŒ
``foo->a``”h]”hŒfoo->a”…””}”(hj°  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj„  ubhŒ and ”…””}”hj„  sbjõ  )”}”(hŒ
``foo->b``”h]”hŒfoo->b”…””}”(hjÂ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj„  ubhŒ in this case.”…””}”(hj„  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KhjÛ  hžhubhé)”}”(hŒaThis data field access is available for the return value via ``$retval``,
e.g. ``$retval->name``.”h]”(hŒ=This data field access is available for the return value via ”…””}”(hjÚ  hžhhŸNh Nubjõ  )”}”(hŒ``$retval``”h]”hŒ$retval”…””}”(hjâ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjÚ  ubhŒ,
e.g. ”…””}”(hjÚ  hžhhŸNh Nubjõ  )”}”(hŒ``$retval->name``”h]”hŒ$retval->name”…””}”(hjô  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjÚ  ubhŒ.”…””}”(hjÚ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KhjÛ  hžhubhé)”}”(hX÷  For these BTF arguments and fields, ``:string`` and ``:ustring`` change the
behavior. If these are used for BTF argument or field, it checks whether
the BTF type of the argument or the data field is ``char *`` or ``char []``,
or not.  If not, it rejects applying the string types. Also, with the BTF
support, you don't need a memory dereference operator (``+0(PTR)``) for
accessing the string pointed by a ``PTR``. It automatically adds the memory
dereference operator according to the BTF type. e.g. ::”h]”(hŒ$For these BTF arguments and fields, ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``:string``”h]”hŒ:string”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ and ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``:ustring``”h]”hŒ:ustring”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ‡ change the
behavior. If these are used for BTF argument or field, it checks whether
the BTF type of the argument or the data field is ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ
``char *``”h]”hŒchar *”…””}”(hj8  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ or ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``char []``”h]”hŒchar []”…””}”(hjJ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ…,
or not.  If not, it rejects applying the string types. Also, with the BTF
support, you donâ€™t need a memory dereference operator (”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``+0(PTR)``”h]”hŒ+0(PTR)”…””}”(hj\  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒ() for
accessing the string pointed by a ”…””}”(hj  hžhhŸNh Nubjõ  )”}”(hŒ``PTR``”h]”hŒPTR”…””}”(hjn  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj  ubhŒW. It automatically adds the memory
dereference operator according to the BTF type. e.g.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h K’hjÛ  hžhubjB  )”}”(hŒ‚# echo 't sched_switch prev->comm:string' >> dynamic_events
# echo 'f getname_flags%return $retval->name:string' >> dynamic_events”h]”hŒ‚# echo 't sched_switch prev->comm:string' >> dynamic_events
# echo 'f getname_flags%return $retval->name:string' >> dynamic_events”…””}”hj†  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KšhjÛ  hžhubhé)”}”(hŒÅThe ``prev->comm`` is an embedded char array in the data structure, and
``$retval->name`` is a char pointer in the data structure. But in both
cases, you can use ``:string`` type to get the string.”h]”(hŒThe ”…””}”(hj”  hžhhŸNh Nubjõ  )”}”(hŒ``prev->comm``”h]”hŒ
prev->comm”…””}”(hjœ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj”  ubhŒ6 is an embedded char array in the data structure, and
”…””}”(hj”  hžhhŸNh Nubjõ  )”}”(hŒ``$retval->name``”h]”hŒ$retval->name”…””}”(hj®  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj”  ubhŒI is a char pointer in the data structure. But in both
cases, you can use ”…””}”(hj”  hžhhŸNh Nubjõ  )”}”(hŒ``:string``”h]”hŒ:string”…””}”(hjÀ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj”  ubhŒ type to get the string.”…””}”(hj”  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KhjÛ  hžhubeh}”(h]”Œbtf-arguments”ah ]”h"]”Œbtf arguments”ah$]”h&]”uh1h´hh¶hžhhŸh³h KRubhµ)”}”(hhh]”(hº)”}”(hŒUsage examples”h]”hŒUsage examples”…””}”(hjã  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjà  hžhhŸh³h K£ubhé)”}”(hŒiHere is an example to add fprobe events on ``vfs_read()`` function entry
and exit, with BTF arguments.
::”h]”(hŒ+Here is an example to add fprobe events on ”…””}”(hjñ  hžhhŸNh Nubjõ  )”}”(hŒ``vfs_read()``”h]”hŒ
vfs_read()”…””}”(hjù  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjñ  ubhŒ- function entry
and exit, with BTF arguments.”…””}”(hjñ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h K¤hjà  hžhubjB  )”}”(hXã   # echo 'f vfs_read $arg*' >> dynamic_events
 # echo 'f vfs_read%return $retval' >> dynamic_events
 # cat dynamic_events
f:fprobes/vfs_read__entry vfs_read file=file buf=buf count=count pos=pos
f:fprobes/vfs_read__exit vfs_read%return arg1=$retval
 # echo 1 > events/fprobes/enable
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] ...1.   335.883195: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883208: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   335.883220: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883224: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   335.883232: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c687a count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883237: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   336.050329: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   336.050343: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1”h]”hXã   # echo 'f vfs_read $arg*' >> dynamic_events
 # echo 'f vfs_read%return $retval' >> dynamic_events
 # cat dynamic_events
f:fprobes/vfs_read__entry vfs_read file=file buf=buf count=count pos=pos
f:fprobes/vfs_read__exit vfs_read%return arg1=$retval
 # echo 1 > events/fprobes/enable
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] ...1.   335.883195: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883208: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   335.883220: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883224: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   335.883232: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c687a count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   335.883237: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1
              sh-70      [000] ...1.   336.050329: vfs_read__entry: (vfs_read+0x4/0x340) file=0xffff888005cf9a80 buf=0x7ffef36c6879 count=1 pos=0xffffc900005aff08
              sh-70      [000] .....   336.050343: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=1”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h K¨hjà  hžhubhé)”}”(hŒPYou can see all function arguments and return values are recorded as signed int.”h]”hŒPYou can see all function arguments and return values are recorded as signed int.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Kºhjà  hžhubhé)”}”(hŒžAlso, here is an example of tracepoint events on ``sched_switch`` tracepoint.
To compare the result, this also enables the ``sched_switch`` traceevent too.
::”h]”(hŒ1Also, here is an example of tracepoint events on ”…””}”(hj-  hžhhŸNh Nubjõ  )”}”(hŒ``sched_switch``”h]”hŒsched_switch”…””}”(hj5  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj-  ubhŒ: tracepoint.
To compare the result, this also enables the ”…””}”(hj-  hžhhŸNh Nubjõ  )”}”(hŒ``sched_switch``”h]”hŒsched_switch”…””}”(hjG  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hj-  ubhŒ traceevent too.”…””}”(hj-  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h K¼hjà  hžhubjB  )”}”(hX   # echo 't sched_switch $arg*' >> dynamic_events
 # echo 1 > events/sched/sched_switch/enable
 # echo 1 > events/tracepoints/sched_switch/enable
 # echo > trace
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] d..2.  3912.083993: sched_switch: prev_comm=sh prev_pid=70 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
              sh-70      [000] d..3.  3912.083995: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffff88800664e100 next=0xffffffff828229c0 prev_state=1
          <idle>-0       [000] d..2.  3912.084183: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=16 next_prio=120
          <idle>-0       [000] d..3.  3912.084184: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffffffff828229c0 next=0xffff888004208000 prev_state=0
     rcu_preempt-16      [000] d..2.  3912.084196: sched_switch: prev_comm=rcu_preempt prev_pid=16 prev_prio=120 prev_state=I ==> next_comm=swapper/0 next_pid=0 next_prio=120
     rcu_preempt-16      [000] d..3.  3912.084196: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffff888004208000 next=0xffffffff828229c0 prev_state=1026
          <idle>-0       [000] d..2.  3912.085191: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=16 next_prio=120
          <idle>-0       [000] d..3.  3912.085191: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffffffff828229c0 next=0xffff888004208000 prev_state=0”h]”hX   # echo 't sched_switch $arg*' >> dynamic_events
 # echo 1 > events/sched/sched_switch/enable
 # echo 1 > events/tracepoints/sched_switch/enable
 # echo > trace
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] d..2.  3912.083993: sched_switch: prev_comm=sh prev_pid=70 prev_prio=120 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
              sh-70      [000] d..3.  3912.083995: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffff88800664e100 next=0xffffffff828229c0 prev_state=1
          <idle>-0       [000] d..2.  3912.084183: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=16 next_prio=120
          <idle>-0       [000] d..3.  3912.084184: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffffffff828229c0 next=0xffff888004208000 prev_state=0
     rcu_preempt-16      [000] d..2.  3912.084196: sched_switch: prev_comm=rcu_preempt prev_pid=16 prev_prio=120 prev_state=I ==> next_comm=swapper/0 next_pid=0 next_prio=120
     rcu_preempt-16      [000] d..3.  3912.084196: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffff888004208000 next=0xffffffff828229c0 prev_state=1026
          <idle>-0       [000] d..2.  3912.085191: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=16 next_prio=120
          <idle>-0       [000] d..3.  3912.085191: sched_switch: (__probestub_sched_switch+0x4/0x10) preempt=0 prev=0xffffffff828229c0 next=0xffff888004208000 prev_state=0”…””}”hj_  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KÀhjà  hžhubhé)”}”(hX  As you can see, the ``sched_switch`` trace-event shows *cooked* parameters, on
the other hand, the ``sched_switch`` tracepoint probe event shows *raw*
parameters. This means you can access any field values in the task
structure pointed by the ``prev`` and ``next`` arguments.”h]”(hŒAs you can see, the ”…””}”(hjm  hžhhŸNh Nubjõ  )”}”(hŒ``sched_switch``”h]”hŒsched_switch”…””}”(hju  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjm  ubhŒ trace-event shows ”…””}”(hjm  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ*cooked*”h]”hŒcooked”…””}”(hj‰  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‡  hjm  ubhŒ$ parameters, on
the other hand, the ”…””}”(hjm  hžhhŸNh Nubjõ  )”}”(hŒ``sched_switch``”h]”hŒsched_switch”…””}”(hj›  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjm  ubhŒ tracepoint probe event shows ”…””}”(hjm  hžhhŸNh Nubjˆ  )”}”(hŒ*raw*”h]”hŒraw”…””}”(hj­  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j‡  hjm  ubhŒ]
parameters. This means you can access any field values in the task
structure pointed by the ”…””}”(hjm  hžhhŸNh Nubjõ  )”}”(hŒ``prev``”h]”hŒprev”…””}”(hj¿  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjm  ubhŒ and ”…””}”(hjm  hžhhŸNh Nubjõ  )”}”(hŒ``next``”h]”hŒnext”…””}”(hjÑ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjm  ubhŒ arguments.”…””}”(hjm  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KÐhjà  hžhubhé)”}”(hŒ…For example, usually ``task_struct::start_time`` is not traced, but with this
traceprobe event, you can trace that field as below.
::”h]”(hŒFor example, usually ”…””}”(hjé  hžhhŸNh Nubjõ  )”}”(hŒ``task_struct::start_time``”h]”hŒtask_struct::start_time”…””}”(hjñ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jô  hjé  ubhŒR is not traced, but with this
traceprobe event, you can trace that field as below.”…””}”(hjé  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h KÕhjà  hžhubjB  )”}”(hX]   # echo 't sched_switch comm=next->comm:string next->start_time' > dynamic_events
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] d..3.  5606.686577: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="rcu_preempt" usage=1 start_time=245000000
     rcu_preempt-16      [000] d..3.  5606.686602: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="sh" usage=1 start_time=1596095526
              sh-70      [000] d..3.  5606.686637: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.687190: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="rcu_preempt" usage=1 start_time=245000000
     rcu_preempt-16      [000] d..3.  5606.687202: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.690317: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000
     kworker/0:1-14      [000] d..3.  5606.690339: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.692368: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000”h]”hX]   # echo 't sched_switch comm=next->comm:string next->start_time' > dynamic_events
 # head -n 20 trace | tail
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
              sh-70      [000] d..3.  5606.686577: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="rcu_preempt" usage=1 start_time=245000000
     rcu_preempt-16      [000] d..3.  5606.686602: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="sh" usage=1 start_time=1596095526
              sh-70      [000] d..3.  5606.686637: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.687190: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="rcu_preempt" usage=1 start_time=245000000
     rcu_preempt-16      [000] d..3.  5606.687202: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.690317: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000
     kworker/0:1-14      [000] d..3.  5606.690339: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="swapper/0" usage=2 start_time=0
          <idle>-0       [000] d..3.  5606.692368: sched_switch: (__probestub_sched_switch+0x4/0x10) comm="kworker/0:1" usage=1 start_time=137000000”…””}”hj	  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h KÙhjà  hžhubhŒtarget”“”)”}”(hŒ!.. _fprobetrace_exit_args_sample:”h]”h}”(h]”h ]”h"]”h$]”h&]”Œrefid”Œfprobetrace-exit-args-sample”uh1j  h Kæhjà  hžhhŸh³ubhé)”}”(hŒÁThe return probe allows us to access the results of some functions, which returns
the error code and its results are passed via function parameter, such as an
structure-initialization function.”h]”hŒÁThe return probe allows us to access the results of some functions, which returns
the error code and its results are passed via function parameter, such as an
structure-initialization function.”…””}”(hj%  hžhhŸNh Nubah}”(h]”j$  ah ]”h"]”Œfprobetrace_exit_args_sample”ah$]”h&]”uh1hèhŸh³h Kèhjà  hžhŒexpect_referenced_by_name”}”j1  j  sŒexpect_referenced_by_id”}”j$  j  subhé)”}”(hŒƒFor example, vfs_open() will link the file structure to the inode and update
mode. You can trace that changes with return probe.
::”h]”hŒ€For example, vfs_open() will link the file structure to the inode and update
mode. You can trace that changes with return probe.”…””}”(hj8  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Kìhjà  hžhubjB  )”}”(hXº  # echo 'f vfs_open mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
# echo 'f vfs_open%%return mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
# echo 1 > events/fprobes/enable
# cat trace
             sh-131     [006] ...1.  1945.714346: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x2 inode=0x0
             sh-131     [006] ...1.  1945.714358: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4d801e inode=0xffff888008470168
            cat-143     [007] ...1.  1945.717949: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
            cat-143     [007] ...1.  1945.717956: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4a801d inode=0xffff888005f78d28
            cat-143     [007] ...1.  1945.720616: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
            cat-143     [007] ...1.  1945.728263: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0xa800d inode=0xffff888004ada8d8”h]”hXº  # echo 'f vfs_open mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
# echo 'f vfs_open%%return mode=file->f_mode:x32 inode=file->f_inode:x64' >> dynamic_events
# echo 1 > events/fprobes/enable
# cat trace
             sh-131     [006] ...1.  1945.714346: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x2 inode=0x0
             sh-131     [006] ...1.  1945.714358: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4d801e inode=0xffff888008470168
            cat-143     [007] ...1.  1945.717949: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
            cat-143     [007] ...1.  1945.717956: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0x4a801d inode=0xffff888005f78d28
            cat-143     [007] ...1.  1945.720616: vfs_open__entry: (vfs_open+0x4/0x40) mode=0x1 inode=0x0
            cat-143     [007] ...1.  1945.728263: vfs_open__exit: (do_open+0x274/0x3d0 <- vfs_open) mode=0xa800d inode=0xffff888004ada8d8”…””}”hjF  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1jA  hŸh³h Kðhjà  hžhubhé)”}”(hŒOYou can see the `file::f_mode` and `file::f_inode` are updated in `vfs_open()`.”h]”(hŒYou can see the ”…””}”(hjT  hžhhŸNh Nubj  )”}”(hŒ`file::f_mode`”h]”hŒfile::f_mode”…””}”(hj\  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjT  ubhŒ and ”…””}”(hjT  hžhhŸNh Nubj  )”}”(hŒ`file::f_inode`”h]”hŒfile::f_inode”…””}”(hjn  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjT  ubhŒ are updated in ”…””}”(hjT  hžhhŸNh Nubj  )”}”(hŒ`vfs_open()`”h]”hŒ
vfs_open()”…””}”(hj€  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjT  ubhŒ.”…””}”(hjT  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hèhŸh³h Kûhjà  hžhubeh}”(h]”Œusage-examples”ah ]”h"]”Œusage examples”ah$]”h&]”uh1h´hh¶hžhhŸh³h K£ubeh}”(h]”Œfprobe-based-event-tracing”ah ]”h"]”Œfprobe-based event tracing”ah$]”h&]”uh1h´hhhžhhŸh³h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h³uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¹NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jË  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h³Œ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”j$  ]”j  asŒnameids”}”(j¥  j¢  j-  j*  j  jŠ  jØ  jÕ  jÝ  jÚ  j  jš  j1  j$  uŒ	nametypes”}”(j¥  ‰j-  ‰j  ‰jØ  ‰jÝ  ‰j  ‰j1  ˆuh}”(j¢  h¶j*  h×jŠ  j0  jÕ  j  jÚ  jÛ  jš  jà  j$  j%  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”hŒsystem_message”“”)”}”(hhh]”hé)”}”(hhh]”hŒBHyperlink target "fprobetrace-exit-args-sample" is not referenced.”…””}”hj5  sbah}”(h]”h ]”h"]”h$]”h&]”uh1hèhj2  ubah}”(h]”h ]”h"]”h$]”h&]”Œlevel”KŒtype”ŒINFO”Œsource”h³Œline”Kæuh1j0  ubaŒtransformer”NŒinclude_log”]”Œ
decoration”Nhžhub.