Messages in this thread | | | Subject | Re: [PATCH v2] printk: add console output tracing | From | Johannes Berg <> | Date | Thu, 24 Nov 2011 20:00:16 +0100 |
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On Thu, 2011-11-24 at 16:45 +0100, Frederic Weisbecker wrote:
> > I don't really feel comfortable modifying the _call_console_drivers() > > function to not handle start > end (modulo log buf size of course), but > > at the same time I don't feel comfortable putting code into it that > > doesn't handle it. > > So, the: > > BUG_ON(((int)(start - end)) > 0); > > check is there to ensure we haven't wrapped INT_MAX. If we have reached > that point it definetly means we have a bug because log_buf_len is itself > an int and we shouldn't overlap INT_MAX.
Ok that makes sense.
> The care on the wrapping that is done in _call_console_drivers() is > different and concerns log_buf_len itself. If log_buf_len = 8, start = 7 > and end = 9, then you will enter the "((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK))" > condition that handle the wrap on LOG_BUF_MASK to print the two chars. > But this is totally different from "start > end" which would mean we have > a bug.
Oh. So we get end = 9 in that case? That seems confusing ... I would have expected end = 1 then! Which is the whole reason I got confused I guess.
> So, in your tracepoint you can safely use "end - start" as a length for your > dynamic array. But the rest of your tracepoint (all the fast assign part) > still needs the masks as you did.
Oh, that's all you were trying to say? I can see that, ok. I just didn't see that end would be 9 instead of 1 and tried to handle that. The _call_console_drivers() code is a bit different I guess.
I'll send a new version.
johannes
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