The hard-coded 16 is used in various bpf progs. These progs get task
comm either via bpf_get_current_comm() or prctl() or
bpf_core_read_str(), all of which can work well even if the task comm size
is changed.

In these BPF programs, one thing to be improved is the
sched:sched_switch tracepoint args. As the tracepoint args are derived
from the kernel, we'd better make it same with the kernel. So the macro
TASK_COMM_LEN is converted to type enum, then all the BPF programs can
get it through BTF.

The BPF program which wants to use TASK_COMM_LEN should include the header
vmlinux.h. Regarding the test_stacktrace_map and test_tracepoint, as the
type defined in linux/bpf.h are also defined in vmlinux.h, so we don't
need to include linux/bpf.h again.

Signed-off-by: Yafang Shao <redacted>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <redacted>
Cc: Andrii Nakryiko <redacted>
Cc: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <redacted>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <redacted>
Cc: Petr Mladek <pmladek@suse.com>
---
 include/linux/sched.h                                   | 9 +++++++--
 tools/testing/selftests/bpf/progs/test_stacktrace_map.c | 6 +++---
 tools/testing/selftests/bpf/progs/test_tracepoint.c     | 6 +++---
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e0454e60fe8f..1c456691f890 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -274,8 +274,13 @@ struct task_group;
 
 #define get_current_state()	READ_ONCE(current->__state)
 
-/* Task command name length: */
-#define TASK_COMM_LEN			16
+/*
+ * Define the task command name length as enum, then it can be visible to
+ * BPF programs.
+ */
+enum {
+	TASK_COMM_LEN = 16,
+};
 
 extern void scheduler_tick(void);
 

diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
index 00ed48672620..e9b602a6dc1b 100644
--- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
+++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2018 Facebook
 
-#include <linux/bpf.h>
+#include <vmlinux.h>
 #include <bpf/bpf_helpers.h>
 
 #ifndef PERF_MAX_STACK_DEPTH

@@ -41,11 +41,11 @@ struct {
 /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
 struct sched_switch_args {
 	unsigned long long pad;
-	char prev_comm[16];
+	char prev_comm[TASK_COMM_LEN];
 	int prev_pid;
 	int prev_prio;
 	long long prev_state;
-	char next_comm[16];
+	char next_comm[TASK_COMM_LEN];
 	int next_pid;
 	int next_prio;
 };

diff --git a/tools/testing/selftests/bpf/progs/test_tracepoint.c b/tools/testing/selftests/bpf/progs/test_tracepoint.c
index 4b825ee122cf..f21982681e28 100644
--- a/tools/testing/selftests/bpf/progs/test_tracepoint.c
+++ b/tools/testing/selftests/bpf/progs/test_tracepoint.c

@@ -1,17 +1,17 @@
 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2017 Facebook
 
-#include <linux/bpf.h>
+#include <vmlinux.h>
 #include <bpf/bpf_helpers.h>
 
 /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
 struct sched_switch_args {
 	unsigned long long pad;
-	char prev_comm[16];
+	char prev_comm[TASK_COMM_LEN];
 	int prev_pid;
 	int prev_prio;
 	long long prev_state;
-	char next_comm[16];
+	char next_comm[TASK_COMM_LEN];
 	int next_pid;
 	int next_prio;
 };

-- 
2.17.1