[PATCH] printk: add pr_line buffering API

[Sergey Senozhatsky]

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 include/linux/printk.h | 63 ++++++++++++++++++++++++++++++++++++++++++
 kernel/printk/printk.c | 55 ++++++++++++++++++++++++++++++++++++
 2 files changed, 118 insertions(+)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index cf3eccfe1543..fc5f11c7579c 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -157,6 +157,15 @@ static inline void printk_nmi_direct_enter(void) { }
 static inline void printk_nmi_direct_exit(void) { }
 #endif /* PRINTK_NMI */
 
+#define PRINTK_PR_LINE_BUF_SZ	80
+
+struct pr_line {
+	char			*buffer;
+	int			size;
+	int			len;
+	char			*level;
+};
+
 #ifdef CONFIG_PRINTK
 asmlinkage __printf(5, 0)
 int vprintk_emit(int facility, int level,
@@ -209,6 +218,30 @@ extern asmlinkage void dump_stack(void) __cold;
 extern void printk_safe_init(void);
 extern void printk_safe_flush(void);
 extern void printk_safe_flush_on_panic(void);
+
+#define DEFINE_PR_LINE(lev, name)				\
+	char		__pr_line_buf[PRINTK_PR_LINE_BUF_SZ];	\
+	struct pr_line	name = {				\
+		.buffer = __pr_line_buf,			\
+		.size 	= PRINTK_PR_LINE_BUF_SZ,		\
+		.len 	= 0,					\
+		.level	= lev,					\
+	}
+
+#define DEFINE_PR_LINE_BUF(lev, name, buf, sz)			\
+	struct pr_line	name = {				\
+		.buffer = buf,					\
+		.size 	= (sz),					\
+		.len 	= 0,					\
+		.level	= lev,					\
+	}
+
+extern __printf(2, 3)
+int pr_line(struct pr_line *pl, const char *fmt, ...);
+extern __printf(2, 0)
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args);
+extern void pr_line_flush(struct pr_line *pl);
+
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -284,6 +317,36 @@ static inline void printk_safe_flush(void)
 static inline void printk_safe_flush_on_panic(void)
 {
 }
+
+#define DEFINE_PR_LINE(lev, name)				\
+	struct pr_line	name = {				\
+		.buffer = NULL,					\
+		.size 	= 0,					\
+		.len 	= 0,					\
+		.level	= lev,					\
+	}
+
+#define DEFINE_PR_LINE_BUF(lev, name, buf, sz)			\
+	struct pr_line	name = {				\
+		.buffer = buf,					\
+		.size 	= 0,					\
+		.len 	= 0,					\
+		.level	= lev,					\
+	}
+
+static inline __printf(2, 3)
+int pr_line(struct pr_line *pl, const char *fmt, ...)
+{
+	return 0;
+}
+static inline __printf(2, 0)
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args)
+{
+	return 0;
+}
+static inline void pr_line_flush(struct pr_line *pl)
+{
+}
 #endif
 
 extern int kptr_restrict;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fd6f8ed28e01..daeb41a57929 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2004,6 +2004,61 @@ asmlinkage __visible int printk(const char *fmt, ...)
 }
 EXPORT_SYMBOL(printk);
 
+#define PR_LINE_TRUNCATED_MSG "** truncated **\n"
+
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args)
+{
+	int len;
+
+	if (unlikely(pl->size >= LOG_LINE_MAX))
+		pl->size = LOG_LINE_MAX - sizeof(PR_LINE_TRUNCATED_MSG);
+
+	if (fmt[0] == '\n') {
+		pr_line_flush(pl);
+		return 0;
+	}
+
+	if (pl->len >= pl->size)
+		return -1;
+
+	len = vsnprintf(pl->buffer + pl->len, pl->size - pl->len, fmt, args);
+	if (pl->len + len >= pl->size) {
+		pl->len = pl->size + 1;
+		return -1;
+	}
+
+	pl->len += len;
+	if (pl->len && pl->buffer[pl->len - 1] == '\n')
+		pr_line_flush(pl);
+	return 0;
+}
+EXPORT_SYMBOL(vpr_line);
+
+int pr_line(struct pr_line *pl, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, fmt);
+	ret = vpr_line(pl, fmt, ap);
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(pr_line);
+
+void pr_line_flush(struct pr_line *pl)
+{
+	if (!pl->len)
+		return;
+
+	if (pl->len < pl->size)
+		printk("%s%.*s", pl->level, pl->len, pl->buffer);
+	else
+		printk("%s%.*s%s", pl->level, pl->len, pl->buffer,
+			PR_LINE_TRUNCATED_MSG);
+	pl->len = 0;
+}
+EXPORT_SYMBOL(pr_line_flush);
 #else /* CONFIG_PRINTK */
 
 #define LOG_LINE_MAX		0
-- 
2.19.0