linux-kernel - [PATCH] timens: show clock symbolic names in /proc/pid/timens

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Date:   Fri, 10 Apr 2020 23:52:09 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrei Vagin <avagin@...il.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH] timens: show clock symbolic names in /proc/pid/timens_offsets

Michael Kerrisk suggested to replace numeric clock IDs on symbolic
names.

Now the content of these files looks like this:
$ cat /proc/5362/timens_offsets
monotonic	   9504000	         0
boottime	   3456000	         0

For setting offsets, both representations of clocks can be used.

As for compatibility, it is acceptable to change things as long as
userspace doesn't care. The format of timens_offsets files is very
new and there are no userspace tools that rely on this format.

But three projects crun, util-linux and criu rely on the interface of
setting time offsets and this is why we need to continue supporting the
clock IDs in this case.

Fixes: 04a8682a71be ("fs/proc: Introduce /proc/pid/timens_offsets")
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: Dmitry Safonov <0x7f454c46@...il.com>
Suggested-by: Michael Kerrisk <mtk.manpages@...il.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
---
 fs/proc/base.c          | 14 +++++++++++++-
 kernel/time/namespace.c | 15 ++++++++++++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6042b646ab27..572898dd16a0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1573,6 +1573,7 @@ static ssize_t timens_offsets_write(struct file *file, const char __user *buf,
 	noffsets = 0;
 	for (pos = kbuf; pos; pos = next_line) {
 		struct proc_timens_offset *off = &offsets[noffsets];
+		char clock[10];
 		int err;
 
 		/* Find the end of line and ensure we don't look past it */
@@ -1584,10 +1585,21 @@ static ssize_t timens_offsets_write(struct file *file, const char __user *buf,
 				next_line = NULL;
 		}
 
-		err = sscanf(pos, "%u %lld %lu", &off->clockid,
+		err = sscanf(pos, "%9s %lld %lu", clock,
 				&off->val.tv_sec, &off->val.tv_nsec);
 		if (err != 3 || off->val.tv_nsec >= NSEC_PER_SEC)
 			goto out;
+
+		clock[sizeof(clock) - 1] = 0;
+		if (strcmp(clock, "monotonic") == 0 ||
+		    strcmp(clock, __stringify(CLOCK_MONOTONIC)) == 0)
+			off->clockid = CLOCK_MONOTONIC;
+		else if (strcmp(clock, "boottime") == 0 ||
+			 strcmp(clock, __stringify(CLOCK_BOOTTIME)) == 0)
+			off->clockid = CLOCK_BOOTTIME;
+		else
+			goto out;
+
 		noffsets++;
 		if (noffsets == ARRAY_SIZE(offsets)) {
 			if (next_line)
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index e6ba064ce773..8127d2647064 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -338,7 +338,20 @@ static struct user_namespace *timens_owner(struct ns_common *ns)
 
 static void show_offset(struct seq_file *m, int clockid, struct timespec64 *ts)
 {
-	seq_printf(m, "%d %lld %ld\n", clockid, ts->tv_sec, ts->tv_nsec);
+	char *clock;
+
+	switch (clockid) {
+	case CLOCK_BOOTTIME:
+		clock = "boottime";
+		break;
+	case CLOCK_MONOTONIC:
+		clock = "monotonic";
+		break;
+	default:
+		clock = "unknown";
+		break;
+	}
+	seq_printf(m, "%s\t%10lld\t%10ld\n", clock, ts->tv_sec, ts->tv_nsec);
 }
 
 void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m)
-- 
2.24.1