Re: [PATCH v6 bpf-next 07/11] tracepoint: introduce kernel_tracepoint_find_by_name

----- On Mar 27, 2018, at 10:07 AM, rostedt rostedt@goodmis.org wrote:

On Mon, 26 Mar 2018 19:47:02 -0700
Alexei Starovoitov [off-list ref] wrote:

quoted

From: Alexei Starovoitov <ast@kernel.org>

introduce kernel_tracepoint_find_by_name() helper to let bpf core
find tracepoint by name and later attach bpf probe to a tracepoint

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Steven showed preference for tracepoint_kernel_find_by_name() at some
point (starting with a tracepoint_ prefix). I'm find with either of
the names.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thanks,

Mathieu

Thanks for doing this Alexei!

One nit below.

quoted

---
 include/linux/tracepoint.h | 6 ++++++
 kernel/tracepoint.c        | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c92f4adbc0d7..a00b84473211 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h

@@ -43,6 +43,12 @@ tracepoint_probe_unregister(struct tracepoint *tp, void

*probe, void *data);
 extern void
 for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
 		void *priv);
+#ifdef CONFIG_TRACEPOINTS
+struct tracepoint *kernel_tracepoint_find_by_name(const char *name);
+#else
+static inline struct tracepoint *
+kernel_tracepoint_find_by_name(const char *name) { return NULL; }
+#endif
 
 #ifdef CONFIG_MODULES
 struct tp_module {

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 671b13457387..e2a9a0391ae2 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c

@@ -528,6 +528,15 @@ void for_each_kernel_tracepoint(void (*fct)(struct

tracepoint *tp, void *priv),
 }
 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
 
+struct tracepoint *kernel_tracepoint_find_by_name(const char *name)
+{
+	struct tracepoint * const *tp = __start___tracepoints_ptrs;
+
+	for (; tp < __stop___tracepoints_ptrs; tp++)
+		if (!strcmp((*tp)->name, name))
+			return *tp;

Usually for cases like this, we prefer to add brackets for the for
block, as it's not a single line below it.

for (; tp < __stop__tracepoints_ptrs; tp++) {
	if (!strcmp((*tp)->name, name))
		return *tp;
}

-- Steve

quoted

+	return NULL;
+}
 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
 
 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com