While monitoring embedded devices that provide access
to the console over a serial port, in order to obtain
kernel logs from containers, it is necessary to include
consoles in the syslog_ns.
This patch adds a new interface named ns_console_unlock,
and use syslog ns as a parameter to dispaly logs from
current syslog namespace on cosoles, not just init_
syslog_ns.
Signed-off-by: Rui Xiang <rui.xiang@xxxxxxxxxx>
---
include/linux/console.h | 1 +
kernel/printk.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 116 insertions(+), 1 deletion(-)
diff --git a/include/linux/console.h b/include/linux/console.h
index 7571a16..4c02fe6 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -148,6 +148,7 @@ extern struct console *console_drivers;
extern void console_lock(void);
extern int console_trylock(void);
extern void console_unlock(void);
+extern void ns_console_unlock(struct syslog_namespace *ns);
extern void console_conditional_schedule(void);
extern void console_unblank(void);
extern struct tty_driver *console_device(int *);
diff --git a/kernel/printk.c b/kernel/printk.c
index b60c1d4..39bb9db 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1684,7 +1684,7 @@ static int ns_vprintk_emit(int facility, int level,
* regardless of whether it actually gets the console semaphore or not.
*/
if (console_trylock_for_printk(this_cpu, ns))
- console_unlock();
+ ns_console_unlock(ns);
lockdep_on();
out_restore_irqs:
@@ -2135,6 +2135,120 @@ out:
}
/**
+ * ns_console_unlock - unlock the console system for syslog_namespace
+ *
+ * Releases the console_lock which the caller holds on the console system
+ * and the console driver list.
+ *
+ * While the console_lock was held, console output may have been buffered
+ * by printk(). If this is the case, syslog_console_unlock(); emits
+ * the output prior to releasing the lock.
+ *
+ * If there is output waiting, we wake /dev/kmsg and syslog() users.
+ *
+ * syslog_console_unlock(); may be called from any context.
+ */
+void ns_console_unlock(struct syslog_namespace *ns)
+{
+ static char text[LOG_LINE_MAX + PREFIX_MAX];
+ static u64 seen_seq;
+ unsigned long flags;
+ bool wake_klogd = false;
+ bool retry;
+
+ if (console_suspended) {
+ up(&console_sem);
+ return;
+ }
+
+ console_may_schedule = 0;
+
+ /* flush buffered message fragment immediately to console */
+ console_cont_flush(text, sizeof(text), ns);
+again:
+ for (;;) {
+ struct log *msg;
+ size_t len;
+ int level;
+
+ raw_spin_lock_irqsave(&ns->logbuf_lock, flags);
+ if (seen_seq != ns->log_next_seq) {
+ wake_klogd = true;
+ seen_seq = ns->log_next_seq;
+ }
+
+ if (ns->console_seq < ns->log_first_seq) {
+ /* messages are gone, move to first one */
+ ns->console_seq = ns->log_first_seq;
+ ns->console_idx = ns->log_first_idx;
+ console_prev = 0;
+ }
+skip:
+ if (ns->console_seq == ns->log_next_seq)
+ break;
+
+ msg = log_from_idx(ns->console_idx, ns);
+ if (msg->flags & LOG_NOCONS) {
+ /*
+ * Skip record we have buffered and already printed
+ * directly to the console when we received it.
+ */
+ ns->console_idx =
+ log_next(ns->console_idx, ns);
+ ns->console_seq++;
+ /*
+ * We will get here again when we register a new
+ * CON_PRINTBUFFER console. Clear the flag so we
+ * will properly dump everything later.
+ */
+ msg->flags &= ~LOG_NOCONS;
+ console_prev = msg->flags;
+ goto skip;
+ }
+
+ level = msg->level;
+ len = msg_print_text(msg, console_prev, false,
+ text, sizeof(text));
+ ns->console_idx =
+ log_next(ns->console_idx, ns);
+ ns->console_seq++;
+ console_prev = msg->flags;
+ raw_spin_unlock(&ns->logbuf_lock);
+
+ stop_critical_timings(); /* don't trace print latency */
+ call_console_drivers(level, text, len);
+ start_critical_timings();
+ local_irq_restore(flags);
+ }
+ console_locked = 0;
+
+ /* Release the exclusive_console once it is used */
+ if (unlikely(exclusive_console))
+ exclusive_console = NULL;
+
+ raw_spin_unlock(&ns->logbuf_lock);
+
+ up(&console_sem);
+
+ /*
+ * Someone could have filled up the buffer again, so re-check if there's
+ * something to flush. In case we cannot trylock the console_sem again,
+ * there's a new owner and the console_unlock() from them will do the
+ * flush, no worries.
+ */
+ raw_spin_lock(&ns->logbuf_lock);
+ retry = ns->console_seq != ns->log_next_seq;
+ raw_spin_unlock_irqrestore(&ns->logbuf_lock, flags);
+
+ if (retry && console_trylock())
+ goto again;
+
+ if (wake_klogd)
+ wake_up_klogd();
+}
+EXPORT_SYMBOL(ns_console_unlock);
+
+/**
* console_unlock - unlock the console system
*
* Releases the console_lock which the caller holds on the console system
--
1.8.2.2
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