Stephen Hemminger wrote:

quoted

The following options come to mind:
1. Keep the msg buffer, but make it smaller.  Around 120 bytes would probably be
big enough for the vast majority of messages.  (printk() uses a 1024-byte buffer,
but it's static -- see #2.)

2. Use a big, static buffer, protected by a spinlock.  printk() does this.

3. Do the whole thing in a macro, as in previous proposals.  The size of the macro
expansion could be reduced somewhat by doing the encode-prefix step in a function --
something like:

[more on #3 snipped]

Is there some way to tack copy and prepend what you want onto the format
string, and add additional arguments to the call to printk?  That way you
wouldn't need space for the potentially large resulting string, but only
enough room for the expanded format string.

Interesting idea.  I pondered this for a while.  But even if you postulate 
a varargs version of printk (which doesn't exist), it's not really
feasible to do this in a function.  There's no way for a function to
prepend args to a va_list.  That means you'd have to encode the text of
the prefix as part of the format string, and that would require you to
allocate room for prefix+format, which is still a lot of stack.  Also,
the fact that the interface name itself may contain "%d" or some such
makes it even messier.

Greg K-H thinks #2 is a reasonable solution (you're about to serialize on printk's
lock anyway), so I'll go with that.

Thanks.
Jim