Some code, most notably the Bluetooth drivers, uses something like
the following:

char buf[80];
snprintf(buf, sizeof(buf), "Driver: %s\n", driver_name);
skb_put_data(skb, buf, strlen(buf));

This looks suboptimal at least because:

1) It yields in BUG() just in case the developer underestimates
   the size of an skb being used;
2) It requires extra data copy from an external buffer;
3) It uses 'strlen()' redundantly because actual data length
   is calculated by 'snprintf()' itself.

So introduce 'skb_printf()' which aims to address all of these
issues. As usual, thoughts and comments are highly appreciated.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
---
 include/linux/skbuff.h |  1 +
 net/core/skbuff.c      | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2bcf78a4de7b..fb4ef55a8f86 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4292,6 +4292,7 @@ int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse);
 int skb_mpls_dec_ttl(struct sk_buff *skb);
 struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
 			     gfp_t gfp);
+int skb_printf(struct sk_buff *skb, const char *fmt, ...);
 
 static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
 {
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7dad68e3b518..051ab4f28c75 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6992,6 +6992,24 @@ struct sk_buff *pskb_extract(struct sk_buff *skb, int off,
 }
 EXPORT_SYMBOL(pskb_extract);
 
+int skb_printf(struct sk_buff *skb, const char *fmt, ...)
+{
+	int len, size = skb_availroom(skb);
+	va_list args;
+
+	va_start(args, fmt);
+	len = vsnprintf(skb_tail_pointer(skb), size, fmt, args);
+	va_end(args);
+
+	if (unlikely(len >= size))
+		return -ENOSPC;
+
+	skb->tail += len;
+	skb->len += len;
+	return len;
+}
+EXPORT_SYMBOL(skb_printf);
+
 /**
  * skb_condense - try to get rid of fragments/frag_list if possible
  * @skb: buffer
-- 
2.53.0