[PATCH -mm v3] replace old hard-coded 16 with TASK_COMM_LEN_16

[Yafang Shao <laoar.shao@gmail.com>]

This is the followup work of task comm cleanups[1].

A new macro TASK_COMM_LEN_16 is introduced to replace old hard-coded 16
in various files, in order to make them grepable. The difference between
TASK_COMM_LEN and TASK_COMM_LEN_16 is:
- TASK_COMM_LEN
  The size should be same with the TASK_COMM_LEN defined in linux/sched.h.
- TASK_COMM_LEN_16
  The size must be a fixed-size 16 no matter what TASK_COMM_LEN is. The
  usage around it is exposed to userspace, so this macro is defined in
  the UAPI header.

[1]. https://lore.kernel.org/lkml/20211120112738.45980-1-laoar.shao@gmail.com/

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
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 <david@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>

---
Changes since v2:
- make TASK_COMM_LEN_16 a single instance (Michal)
- merge all the patches into a single patch

Changes since v1:
- use TASK_COMM_LEN_16 instead of TASK_COMM_LEN in patch #3 (Steven)
- avoid changing samples/bpf and bpf/progs (Alexei)
---
 include/linux/elfcore-compat.h    | 8 ++------
 include/linux/elfcore.h           | 9 ++-------
 include/uapi/linux/cn_proc.h      | 3 ++-
 include/uapi/linux/sched.h        | 7 +++++++
 tools/include/uapi/linux/sched.h  | 7 +++++++
 tools/perf/tests/evsel-tp-sched.c | 7 ++++---
 6 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
index 54feb64e9b5d..319daa69bb23 100644
--- a/include/linux/elfcore-compat.h
+++ b/include/linux/elfcore-compat.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_ELFCORE_COMPAT_H
 #define _LINUX_ELFCORE_COMPAT_H
 
+#include <uapi/linux/sched.h>
 #include <linux/elf.h>
 #include <linux/elfcore.h>
 #include <linux/compat.h>
@@ -43,12 +44,7 @@ struct compat_elf_prpsinfo
 	__compat_uid_t			pr_uid;
 	__compat_gid_t			pr_gid;
 	compat_pid_t			pr_pid, pr_ppid, pr_pgrp, pr_sid;
-	/*
-	 * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
-	 * changed as it is exposed to userspace. We'd better make it hard-coded
-	 * here.
-	 */
-	char				pr_fname[16];
+	char				pr_fname[TASK_COMM_LEN_16];
 	char				pr_psargs[ELF_PRARGSZ];
 };
 
diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
index 746e081879a5..d3bb4bd3c985 100644
--- a/include/linux/elfcore.h
+++ b/include/linux/elfcore.h
@@ -65,13 +65,8 @@ struct elf_prpsinfo
 	__kernel_gid_t	pr_gid;
 	pid_t	pr_pid, pr_ppid, pr_pgrp, pr_sid;
 	/* Lots missing */
-	/*
-	 * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
-	 * changed as it is exposed to userspace. We'd better make it hard-coded
-	 * here.
-	 */
-	char	pr_fname[16];	/* filename of executable */
-	char	pr_psargs[ELF_PRARGSZ];	/* initial part of arg list */
+	char	pr_fname[TASK_COMM_LEN_16];	/* filename of executable */
+	char	pr_psargs[ELF_PRARGSZ];		/* initial part of arg list */
 };
 
 static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
diff --git a/include/uapi/linux/cn_proc.h b/include/uapi/linux/cn_proc.h
index db210625cee8..88e645230ea5 100644
--- a/include/uapi/linux/cn_proc.h
+++ b/include/uapi/linux/cn_proc.h
@@ -20,6 +20,7 @@
 #define _UAPICN_PROC_H
 
 #include <linux/types.h>
+#include "sched.h"
 
 /*
  * Userspace sends this enum to register with the kernel that it is listening
@@ -110,7 +111,7 @@ struct proc_event {
 		struct comm_proc_event {
 			__kernel_pid_t process_pid;
 			__kernel_pid_t process_tgid;
-			char           comm[16];
+			char           comm[TASK_COMM_LEN_16];
 		} comm;
 
 		struct coredump_proc_event {
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 3bac0a8ceab2..490fd5d48378 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -145,4 +145,11 @@ struct clone_args {
 			 SCHED_FLAG_KEEP_ALL		| \
 			 SCHED_FLAG_UTIL_CLAMP)
 
+/*
+ * For the one which is exposed to userspace and thus can't be changed.
+ */
+enum {
+	TASK_COMM_LEN_16 = 16,
+};
+
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/tools/include/uapi/linux/sched.h b/tools/include/uapi/linux/sched.h
index 3bac0a8ceab2..490fd5d48378 100644
--- a/tools/include/uapi/linux/sched.h
+++ b/tools/include/uapi/linux/sched.h
@@ -145,4 +145,11 @@ struct clone_args {
 			 SCHED_FLAG_KEEP_ALL		| \
 			 SCHED_FLAG_UTIL_CLAMP)
 
+/*
+ * For the one which is exposed to userspace and thus can't be changed.
+ */
+enum {
+	TASK_COMM_LEN_16 = 16,
+};
+
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/tools/perf/tests/evsel-tp-sched.c b/tools/perf/tests/evsel-tp-sched.c
index cf4da3d748c2..0b74bf2ca1ce 100644
--- a/tools/perf/tests/evsel-tp-sched.c
+++ b/tools/perf/tests/evsel-tp-sched.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/err.h>
+#include <linux/sched.h>
 #include <traceevent/event-parse.h>
 #include "evsel.h"
 #include "tests.h"
@@ -43,7 +44,7 @@ static int test__perf_evsel__tp_sched_test(struct test_suite *test __maybe_unuse
 		return -1;
 	}
 
-	if (evsel__test_field(evsel, "prev_comm", 16, false))
+	if (evsel__test_field(evsel, "prev_comm", TASK_COMM_LEN_16, false))
 		ret = -1;
 
 	if (evsel__test_field(evsel, "prev_pid", 4, true))
@@ -55,7 +56,7 @@ static int test__perf_evsel__tp_sched_test(struct test_suite *test __maybe_unuse
 	if (evsel__test_field(evsel, "prev_state", sizeof(long), true))
 		ret = -1;
 
-	if (evsel__test_field(evsel, "next_comm", 16, false))
+	if (evsel__test_field(evsel, "next_comm", TASK_COMM_LEN_16, false))
 		ret = -1;
 
 	if (evsel__test_field(evsel, "next_pid", 4, true))
@@ -73,7 +74,7 @@ static int test__perf_evsel__tp_sched_test(struct test_suite *test __maybe_unuse
 		return -1;
 	}
 
-	if (evsel__test_field(evsel, "comm", 16, false))
+	if (evsel__test_field(evsel, "comm", TASK_COMM_LEN_16, false))
 		ret = -1;
 
 	if (evsel__test_field(evsel, "pid", 4, true))
-- 
2.17.1