Re: [PATCH] i2c: add extra check to safe DMA buffer helper

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On Tue, Mar 12, 2019 at 2:46 AM Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote:
>
>
> > How about also printing some warning if threshold is zero? Since
>
> Hmm, not a warning because a user of a kernel can't do much about it. A
> debug might make sense; it is for developers and will be compiled away
> for production use.
>
> > caller might expect that if msg->len >= threshold, they will get valid
> > pointer. But they will get valid pointer if (msg->len, threshold) is
> > (>0, 0) and NULL if (=0, 0). So warn them that the threshold is bogus.
>
> Well, callers should always check for NULL because a valid pointer can
> not be guaranteed (ENOMEM case). And I still don't get why would you
> want a valid DMA-able pointer if the msg length is 0?

Yes. But I think the debug message here is just to tell caller that
threshold == 0 might not make sense. For threshold > 0, msg->len >=
threshold returns valid. But it's not the case when threshold is 0.
Also, threshold is 0 and 1 behaves the same: msg->len == 0 returns
NULL, msg->len > 0 returns valid.

>
> Thanks!
>
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