On Mon, Oct 29, 2012 at 01:59:35PM -0700, Andrew Morton wrote:
> On Fri, 26 Oct 2012 15:56:57 +0800
> Yuanhan Liu <yuanhan....@linux.intel.com> wrote:
>
> > Say, if we want to allocate a filo with size of 6 bytes, it would be safer
> > to allocate 8 bytes instead of 4 bytes.
> >
> > ...
> >
> > --- a/kernel/kfifo.c
> > +++ b/kernel/kfifo.c
> > @@ -39,11 +39,11 @@ int __kfifo_alloc(struct __kfifo *fifo, unsigned int
> > size,
> > size_t esize, gfp_t gfp_mask)
> > {
> > /*
> > - * round down to the next power of 2, since our 'let the indices
> > + * round up to the next power of 2, since our 'let the indices
> > * wrap' technique works only in this case.
> > */
> > if (!is_power_of_2(size))
> > - size = rounddown_pow_of_two(size);
> > + size = roundup_pow_of_two(size);
> >
> > fifo->in = 0;
> > fifo->out = 0;
> > @@ -84,7 +84,7 @@ int __kfifo_init(struct __kfifo *fifo, void *buffer,
> > size /= esize;
> >
> > if (!is_power_of_2(size))
> > - size = rounddown_pow_of_two(size);
> > + size = roundup_pow_of_two(size);
> >
> > fifo->in = 0;
> > fifo->out = 0;
>
> hm, well, if the user asked for a 100-element fifo then it is a bit
> strange and unexpected to give them a 128-element one.
Hi Andrew,
Yes, and I guess the same to give them a 64-element one.
>
> If there's absolutely no prospect that the kfifo code will ever support
> 100-byte fifos then I guess we should rework the API so that the caller
> has to pass in log2 of the size, not the size itself. That way there
> will be no surprises and no mistakes.
>
> That being said, the power-of-2 limitation isn't at all intrinsic to a
> fifo, so we shouldn't do this. Ideally, we'd change the kfifo
> implementation so it does what the caller asked it to do!
I'm fine with removing the power-of-2 limitation. Stefani, what's your
comment on that?
--yliu
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
