[Devel] [PATCH rh7 1/2] kmsg: Virtualize timestamps in /dev/ksmg output

[Konstantin Khorenko]

Internally log messages contain the timestamps relative to the Host boot
time, while Container could start much later than the Host boots and the
timestamps should be shifted accordingly.

Otherwise "dmesg -H" reports data from the future.

https://jira.sw.ru/browse/PSBM-145263

Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 kernel/printk.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/printk.c b/kernel/printk.c
index 5380594d231f..27221d15590a 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -555,6 +555,7 @@ static ssize_t devkmsg_writev(struct kiocb *iocb, const struct iovec *iv,
 static ssize_t devkmsg_read(struct file *file, char __user *buf,
 			    size_t count, loff_t *ppos)
 {
+	struct ve_struct *ve;
 	struct log_state *log = ve_log_state();
 	struct devkmsg_user *user = file->private_data;
 	struct log *msg;
@@ -597,6 +598,13 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 
 	msg = log_from_idx(log, user->idx);
 	ts_usec = msg->ts_nsec;
+
+	/* shift the timestamp on the Container uptime value */
+	ve = get_exec_env();
+	if (!ve_is_super(ve)) {
+		ts_usec -= ve->real_start_timespec.tv_sec * NSEC_PER_SEC;
+		ts_usec -= ve->real_start_timespec.tv_nsec;
+	}
 	do_div(ts_usec, 1000);
 
 	/*
-- 
2.24.3