Re: Event logging vs enhancing printk

[Andrew Morton <akpm@zip.com.au>]

"Martin J. Bligh" wrote:
> 
> ...
> for (i=0; i<10; i++) { printk ("%d ", i); } printk("\n");
> 
> and CPU 1 does "printk("hello\n");" then instead of getting either
> 
> 0 1 2 3 4 5 6 7 8 9
> hello
> 
> or
> 
> hello
> 0 1 2 3 4 5 6 7 8 9
> 
> either of which would be fine, we may get
> 
> 0 1 2 3 hello
> 4 5 6 7 8 9
> 
> which I don't think is fine - obviously the example is somewhat
> trite, but with the real instances of things that build output for one
> line through multiple calls to printk, you can get unreadable garbage,
> if I read the code correctly ?

Ah.  Yes, that will definitely happen.  We only have atomicity
at the level of a single printk call.

It would be feasible to introduce additional locking so that
multiple printks can be made atomic.  This should be resisted
though - printk needs to be really robust, and needs to have
a good chance of working even when the machine is having hysterics.
It's already rather complex.

For the rare cases which you cite we can use a local staging
buffer and sprintf, or just live with it, I suspect.

-