On Mon, Feb 12, 2024 at 08:56:32AM +0100, Herve Codina wrote:
> The bitmap_onto() function translates one bitmap relative to another but
> no function are present to perform the reverse translation.
>
> Introduce bitmap_off() to fill this hole.
>
> Signed-off-by: Herve Codina <herve.cod...@bootlin.com>
> ---
> include/linux/bitmap.h | 3 +++
> lib/bitmap.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 99451431e4d6..5ecfcbbc91f4 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -65,6 +65,7 @@ struct device;
> * bitmap_remap(dst, src, old, new, nbits) *dst = map(old, new)(src)
> * bitmap_bitremap(oldbit, old, new, nbits) newbit = map(old,
> new)(oldbit)
> * bitmap_onto(dst, orig, relmap, nbits) *dst = orig relative to
> relmap
> + * bitmap_off(dst, orig, relmap, nbits) *dst = bitmap_onto() reverse
> operation
> * bitmap_fold(dst, orig, sz, nbits) dst bits = orig bits mod sz
> * bitmap_parse(buf, buflen, dst, nbits) Parse bitmap dst from kernel
> buf
> * bitmap_parse_user(ubuf, ulen, dst, nbits) Parse bitmap dst from user
> buf
> @@ -208,6 +209,8 @@ int bitmap_bitremap(int oldbit,
> const unsigned long *old, const unsigned long *new, int bits);
> void bitmap_onto(unsigned long *dst, const unsigned long *orig,
> const unsigned long *relmap, unsigned int bits);
> +void bitmap_off(unsigned long *dst, const unsigned long *orig,
> + const unsigned long *relmap, unsigned int bits);
> void bitmap_fold(unsigned long *dst, const unsigned long *orig,
> unsigned int sz, unsigned int nbits);
>
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 2feccb5047dc..71343967335e 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -682,6 +682,48 @@ void bitmap_onto(unsigned long *dst, const unsigned long
> *orig,
> }
> EXPORT_SYMBOL(bitmap_onto);
>
> +/**
> + * bitmap_off - revert operation done by bitmap_onto()
This is definitely a bad name. I've no a better idea, but even
bitmap_onto_revert() would be better.
> + * @dst: resulting translated bitmap
> + * @orig: original untranslated bitmap
> + * @relmap: bitmap relative to which translated
> + * @bits: number of bits in each of these bitmaps
> + *
> + * Suppose onto computed using bitmap_onto(onto, src, relmap, n)
> + * The operation bitmap_off(result, onto, relmap, n) leads to a
> + * result equal or equivalent to src.
Agree with Rasmus. This should be well tested.
> + * The result can be 'equivalent' because bitmap_onto() and
> + * bitmap_off() are not bijective.
> + * The result and src values are equivalent in that sense that a
> + * call to bitmap_onto(onto, src, relmap, n) and a call to
> + * bitmap_onto(onto, result, relmap, n) will lead to the same onto
> + * value.
Did you mean "a call to bitmap_onto(onto, src, relmap, n) and a
call to bitmap_off(onto, result, relmap, n)"?
I think the whole paragraph adds more confusion than explanations.
If a new function is supposed to revert the result of some other
function, I'd better focus on testing that it actually reverts as
advertised, and keep description as brief as possible.
> + * If either of @orig or @relmap is empty (no set bits), then @dst
> + * will be returned empty.
Is this an exception from the 'revert' policy? Doesn't look like that.
So, what for mentioning this specific case?
> + * All bits in @dst not set by the above rule are cleared.
The above rule is about empty @orig and @relmap, not about setting
bits. What did you mean here?
> + */
> +void bitmap_off(unsigned long *dst, const unsigned long *orig,
> + const unsigned long *relmap, unsigned int bits)
> +{
> + unsigned int n, m; /* same meaning as in above comment */
In the above comment, n means the size of bitmaps, and m is not
mentioned at all.
> + if (dst == orig) /* following doesn't handle inplace mappings */
> + return;
> + bitmap_zero(dst, bits);
Can you add an empty line after 'return'.
> + m = 0;
> + for_each_set_bit(n, relmap, bits) {
> + /* m == bitmap_pos_to_ord(relmap, n, bits) */
Don't think we need this comment here. If you want to underline that
m tracks bit order, can you just give it a more explanatory name. For
example, 'bit_order'.
> + if (test_bit(n, orig))
> + set_bit(m, dst);
> + m++;
> + }
> +}
> +EXPORT_SYMBOL(bitmap_off);
> +
> #ifdef CONFIG_NUMA
> /**
> * bitmap_fold - fold larger bitmap into smaller, modulo specified size
> --
> 2.43.0
