On Tue, Jan 27, 2026 at 03:58:13PM +0200, Jani Nikula wrote: > On Tue, 27 Jan 2026, Cristian Ciocaltea <[email protected]> > wrote: > > Currently DIV_ROUND_CLOSEST() is only available for the kernel via > > include/linux/math.h. > > > > Expose it to userland as well by adding __KERNEL_DIV_ROUND_CLOSEST() as > > a common definition in uapi. > > > > Additionally, ensure it allows building ISO C applications by switching > > from the 'typeof' GNU extension to the ISO-friendly __typeof__. > > I am not convinced that it's a good idea to make the implementation of > kernel DIV_ROUND_CLOSEST() part of the kernel UAPI, which is what this > change effectively does. > > I'd at least like to get an ack from Andy Shevchenko first (Cc'd).
Thanks for Cc'ing me! So, the history of the DIV_ROUND_UP() to appear in UAPI is a response to the ethtool change that missed the fact that this was a kernel internal macro. Giving a precedent there is no technical issues to add DIV_ROUND_CLOSEST() to UAPI as proposed. Main question here is: Does DRM headers in question (that are going to use it) really need this? Interestingly that DRM also started using __KERNEL_DIV_ROUND_UP() in UAPI at some point, which kinda makes an argument for allowing the other one. Also fun fact: this series plead for a new macro for division while ignoring existing (UAPI) macros for masks and bits. 0xffffU is effectively __GENMASK(15, 0). (And if you change the code, avoid using variables inside GENMASK() macros, it may generate an awful code, the GENMASK($HI, $LO) << foo is preferred over GENMASK(foo + $DELTA, foo) case. GENMASK(foo - 1, 0) OTOH is fine, however be always careful against overflows with left shifts, as BIT(foo) - 1 may not work for foo == 32, while GENMASK() may not work for foo == 0). So, I have no objections for either choice Acked-by: Andy Shevchenko <[email protected]> ... But if you go that direction, please, fix up the style. > > +/* > > + * Divide positive or negative dividend by positive or negative divisor > > + * and round to closest integer. Result is undefined for negative > > + * divisors if the dividend variable type is unsigned and for negative > > + * dividends if the divisor variable type is unsigned. > > + */ > > +#define __KERNEL_DIV_ROUND_CLOSEST(x, divisor)( \ > > +{ \ Use ({ on this line together... > > + __typeof__(x) __x = x; \ > > + __typeof__(divisor) __d = divisor; \ + blank line here. > > + (((__typeof__(x))-1) > 0 || \ > > + ((__typeof__(divisor))-1) > 0 || \ > > + (((__x) > 0) == ((__d) > 0))) ? \ > > + (((__x) + ((__d) / 2)) / (__d)) : \ > > + (((__x) - ((__d) / 2)) / (__d)); \ > > +} \ > > +) ...as here join }) to be a single line. + blank line. > > #endif /* _UAPI_LINUX_CONST_H */ -- With Best Regards, Andy Shevchenko
