Re: [RFC PATCH] net: skb: on zero-copy formatted output to skb

[Andrew Lunn <andrew@lunn.ch>]

> +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;

A quick look in drivers/bluetooth suggests that none of them care
about truncation, at least they don't check the return code. Maybe it
would be better to truncate than return an error?

I would also try to make the behaviour consistent with the normal
sprintf(), or snprintf(). You want to give users some idea what it is
doing based on its name. It is well known that snprintf() will
truncate, and does not return an error code. sprintf() will just
overwrite the end of the buffer and not return an error code etc.

However calling this skb_snprintf() would be odd, since you don't
actually pass size. But it hints at what it does.

So please add some kerneldoc describing what it actually does.

Please also annotate the const char *fmt, so the compiler can do
format string checks, parameter counting etc.

	Andrew