linux-kernel - [RFC PATCH 7/9] docs: tracing: Update fprobe documentation

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Date:   Wed,  9 Nov 2022 00:50:16 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     linux-trace-kernel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        mhiramat@...nel.org, Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>
Subject: [RFC PATCH 7/9] docs: tracing: Update fprobe documentation

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Update fprobe.rst for
 - the private entry_data argument
 - the return value of the entry handler
 - the nr_rethook_node field.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 Documentation/trace/fprobe.rst |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/fprobe.rst b/Documentation/trace/fprobe.rst
index b64bec1ce144..40dd2fbce861 100644
--- a/Documentation/trace/fprobe.rst
+++ b/Documentation/trace/fprobe.rst
@@ -87,14 +87,16 @@ returns as same as unregister_ftrace_function().
 The fprobe entry/exit handler
 =============================
 
-The prototype of the entry/exit callback function is as follows:
+The prototype of the entry/exit callback function are as follows:
 
 .. code-block:: c
 
- void callback_func(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
+ int entry_callback(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs, void *entry_data);
 
-Note that both entry and exit callbacks have same ptototype. The @entry_ip is
-saved at function entry and passed to exit handler.
+ void exit_callback(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs, void *entry_data);
+
+Note that the @entry_ip is saved at function entry and passed to exit handler.
+If the entry callback function returns !0, the corresponding exit callback will be cancelled.
 
 @fp
         This is the address of `fprobe` data structure related to this handler.
@@ -113,6 +115,12 @@ saved at function entry and passed to exit handler.
         to use @entry_ip. On the other hand, in the exit_handler, the instruction
         pointer of @regs is set to the currect return address.
 
+@...ry_data
+        This is a local storage to share the data between entry and exit handlers.
+        This storage is NULL by default. If the user specify `exit_handler` field
+        and `entry_data_size` field when registering the fprobe, the storage is
+        allocated and passed to both `entry_handler` and `exit_handler`.
+
 Share the callbacks with kprobes
 ================================