[PATCH 8/9] syslog_ns: implement ns_printk for specific syslog_ns

[Rui Xiang <rui.xiang@huawei.com>]

Add a new interface named ns_printk, and assign an
patamater ns. Log which belong to a container can
be printed by ns_printk.

Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
---
 include/linux/printk.h |  4 ++++
 kernel/printk.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 29e3f85..bf83ad9 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -6,6 +6,7 @@
 #include <linux/kern_levels.h>
 #include <linux/linkage.h>
 
+struct syslog_namespace;
 extern const char linux_banner[];
 extern const char linux_proc_banner[];
 
@@ -123,6 +124,9 @@ asmlinkage int printk_emit(int facility, int level,
 asmlinkage __printf(1, 2) __cold
 int printk(const char *fmt, ...);
 
+asmlinkage __printf(2, 3) __cold
+int ns_printk(struct syslog_namespace *ns, const char *fmt, ...);
+
 /*
  * Special printk facility for scheduler use only, _DO_NOT_USE_ !
  */
diff --git a/kernel/printk.c b/kernel/printk.c
index 6b561db..56a8b27 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1554,9 +1554,10 @@ static size_t cont_print_text(char *text, size_t size)
 	return textlen;
 }
 
-asmlinkage int vprintk_emit(int facility, int level,
-			    const char *dict, size_t dictlen,
-			    const char *fmt, va_list args)
+static int ns_vprintk_emit(int facility, int level,
+			const char *dict, size_t dictlen,
+			const char *fmt, va_list args,
+			struct syslog_namespace *ns)
 {
 	static int recursion_bug;
 	static char textbuf[LOG_LINE_MAX];
@@ -1566,7 +1567,6 @@ asmlinkage int vprintk_emit(int facility, int level,
 	unsigned long flags;
 	int this_cpu;
 	int printed_len = 0;
-	struct syslog_namespace *ns = &init_syslog_ns;
 
 	boot_delay_msec(level);
 	printk_delay();
@@ -1697,6 +1697,14 @@ out_restore_irqs:
 
 	return printed_len;
 }
+
+asmlinkage int vprintk_emit(int facility, int level,
+				const char *dict, size_t dictlen,
+				const char *fmt, va_list args)
+{
+	return ns_vprintk_emit(facility, level, dict, dictlen, fmt, args,
+				&init_syslog_ns);
+}
 EXPORT_SYMBOL(vprintk_emit);
 
 asmlinkage int vprintk(const char *fmt, va_list args)
@@ -1762,6 +1770,43 @@ asmlinkage int printk(const char *fmt, ...)
 }
 EXPORT_SYMBOL(printk);
 
+/**
+ * ns_printk - print a kernel message in syslog_ns
+ * @ns: syslog namespace
+ * @fmt: format string
+ *
+ * This is ns_printk().
+ * It can be called from container context. We add a param
+ * ns to record current syslog namespace, because we need to
+ * print some log which are not generated by host, but contaner.
+ *
+ * See the vsnprintf() documentation for format string extensions over C99.
+ **/
+asmlinkage int ns_printk(struct syslog_namespace *ns,
+					const char *fmt, ...)
+{
+	va_list args;
+	int r;
+
+	if (!ns)
+		ns = current_user_ns()->syslog_ns;
+
+#ifdef CONFIG_KGDB_KDB
+	if (unlikely(kdb_trap_printk)) {
+		va_start(args, fmt);
+		r = vkdb_printf(fmt, args);
+		va_end(args);
+		return r;
+	}
+#endif
+	va_start(args, fmt);
+	r = ns_vprintk_emit(0, -1, NULL, 0, fmt, args, ns);
+	va_end(args);
+
+	return r;
+}
+EXPORT_SYMBOL(ns_printk);
+
 #else /* CONFIG_PRINTK */
 
 #define LOG_LINE_MAX		0
-- 
1.8.2.2