[lxc-devel] [lxcfs/master] virtualize the 'btime' field of /proc/stat

[almostivan on Github]

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From 9ac264cfb0836a013af6fa31a4e4c01afe72255a Mon Sep 17 00:00:00 2001
From: Jason Baron <jbaron at akamai.com>
Date: Fri, 27 Jan 2017 16:57:54 -0500
Subject: [PATCH] virtualize the 'btime' field of /proc/stat

Currently, the 'btime' of /proc/stat reflects the boot time of the host.
We would like it to reflect when the guest boots, so use the start time of
init.

Signed-off-by: Jason Baron <jbaron at akamai.com>
---
 bindings.c | 47 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/bindings.c b/bindings.c
index a23c349..8973df8 100644
--- a/bindings.c
+++ b/bindings.c
@@ -3450,6 +3450,27 @@ static int proc_cpuinfo_read(char *buf, size_t size, off_t offset,
 	return rv;
 }
 
+static long int getreaperctime(pid_t pid)
+{
+	char fnam[100];
+	struct stat sb;
+	int ret;
+	pid_t qpid;
+
+	qpid = lookup_initpid_in_store(pid);
+	if (qpid <= 0)
+		return 0;
+
+	ret = snprintf(fnam, 100, "/proc/%d", qpid);
+	if (ret < 0 || ret >= 100)
+		return 0;
+
+	if (lstat(fnam, &sb) < 0)
+		return 0;
+
+	return sb.st_ctime;
+}
+
 static int proc_stat_read(char *buf, size_t size, off_t offset,
 		struct fuse_file_info *fi)
 {
@@ -3513,7 +3534,10 @@ static int proc_stat_read(char *buf, size_t size, off_t offset,
 			continue;
 		if (sscanf(line, "cpu%9[^ ]", cpu_char) != 1) {
 			/* not a ^cpuN line containing a number N, just print it */
-			l = snprintf(cache, cache_size, "%s", line);
+			if (strncmp(line, "btime", 5) == 0)
+				l = snprintf(cache, cache_size, "btime %ld\n", getreaperctime(fc->pid));
+			else
+				l = snprintf(cache, cache_size, "%s", line);
 			if (l < 0) {
 				perror("Error writing to cache");
 				rv = 0;
@@ -3603,23 +3627,12 @@ static int proc_stat_read(char *buf, size_t size, off_t offset,
 
 static long int getreaperage(pid_t pid)
 {
-	char fnam[100];
-	struct stat sb;
-	int ret;
-	pid_t qpid;
-
-	qpid = lookup_initpid_in_store(pid);
-	if (qpid <= 0)
-		return 0;
-
-	ret = snprintf(fnam, 100, "/proc/%d", qpid);
-	if (ret < 0 || ret >= 100)
-		return 0;
-
-	if (lstat(fnam, &sb) < 0)
-		return 0;
+	long int ctime;
 
-	return time(NULL) - sb.st_ctime;
+	ctime = getreaperctime(pid);
+	if (ctime)
+		return time(NULL) - ctime;
+	return ctime;
 }
 
 static unsigned long get_reaper_busy(pid_t task)