printk: Provide helper for message prepending

In order to support prepending different texts to printk
messages, split out the prepending code into a helper
function.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

Author: jogness

kernel/printk/printk.c

@@ -2843,30 +2843,31 @@ static void __console_unlock(void)
 #ifdef CONFIG_PRINTK
 
 /*
- * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This
- * is achieved by shifting the existing message over and inserting the dropped
- * message.
+ * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting
+ * the existing message over and inserting the scratchbuf message.
  *
- * @pmsg is the printk message to prepend.
- *
- * @dropped is the dropped count to report in the dropped message.
+ * @pmsg is the original printk message.
+ * @fmt is the printf format of the message which will prepend the existing one.
  *
- * If the message text in @pmsg->pbufs->outbuf does not have enough space for
- * the dropped message, the message text will be sufficiently truncated.
+ * If there is not enough space in @pmsg->pbufs->outbuf, the existing
+ * message text will be sufficiently truncated.
  *
  * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
  */
-void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+__printf(2, 3)
+static void console_prepend_message(struct printk_message *pmsg, const char *fmt, ...)
 {
 	struct printk_buffers *pbufs = pmsg->pbufs;
 	const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
 	const size_t outbuf_sz = sizeof(pbufs->outbuf);
 	char *scratchbuf = &pbufs->scratchbuf[0];
 	char *outbuf = &pbufs->outbuf[0];
+	va_list args;
 	size_t len;
 
-	len = scnprintf(scratchbuf, scratchbuf_sz,
-		       "** %lu printk messages dropped **\n", dropped);
+	va_start(args, fmt);
+	len = vscnprintf(scratchbuf, scratchbuf_sz, fmt, args);
+	va_end(args);
 
 	/*
 	 * Make sure outbuf is sufficiently large before prepending.
@@ -2888,6 +2889,19 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
 	pmsg->outbuf_len += len;
 }
 
+/*
+ * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message".
+ * @pmsg->outbuf_len is updated appropriately.
+ *
+ * @pmsg is the printk message to prepend.
+ *
+ * @dropped is the dropped count to report in the dropped message.
+ */
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+{
+	console_prepend_message(pmsg, "** %lu printk messages dropped **\n", dropped);
+}
+
 /*
  * Read and format the specified record (or a later record if the specified
  * record is not available).