On Tue, Jan 09, 2018 at 12:29:23AM +0100, Rasmus Villemoes wrote: > On 28 December 2017 at 16:00, Yury Norov <[email protected]> wrote: > > > > In this patch, bitmap_copy_safe and bitmap_{from,to}_arr32 are introduced. > > > > 'Safe' in bitmap_copy_safe() stands for clearing unused bits in bitmap > > beyond last bit till the end of last word. It is useful for hardening > > API when bitmap is assumed to be exposed to userspace. > > I agree completely with getting rid of the complexity of the u32array > functions, and also think they should simply be implemented as a > memcpy() when possible. > > I'm not a fan of the _safe suffix, though. It doesn't say what it's > safe from. For example, one possible interpretation is that it allows > src or dst to be NULL (becoming a noop in such a case). Why not say > what it does? _clear_tail, _clear_rest, something like that.
OK, _clear_tail sounds good. I have to send v2 anyway because there's new driver coming that uses u32array, and I'll also do rename. https://www.spinics.net/lists/arm-kernel/msg627220.html > Or maybe, > can we simply make bitmap_copy behave that way? Hm, probably not, a > bit too many users to check they'd all be ok with that. Yep, and there's explicit comment in lib/bitmap.c: * The possible unused bits in the last, partially used word * of a bitmap are 'don't care'. The implementation makes * no particular effort to keep them zero. It ensures that * their value will not affect the results of any operation. * The bitmap operations that return Boolean (bitmap_empty, * for example) or scalar (bitmap_weight, for example) results * carefully filter out these unused bits from impacting their * results. Changing this may potentially affect performance, and anyway, too revolutionary to me. Yury
