On Sun, Jan 13, 2019 at 08:49:36AM -0800, Matthew Wilcox wrote: > On Thu, Jan 10, 2019 at 11:48:13PM +0000, Jason Gunthorpe wrote: > > +The Linux kernel bool type is an alias for the C99 _Bool type. bool values can > > +only evaluate to 0 or 1, and implicit or explicit conversion to bool > > +automatically converts the value to true or false. When using bool types the > > +!! construction is not needed, which eliminates a class of bugs. > > + > > +When working with bool values the true and false definitions should be used > > +instead of 0 and 1. > > + > > +bool function return types and stack variables are always fine to use whenever > > +appropriate. Use of bool is encouraged to improve readability and is often a > > +better option than 'int' for storing boolean values. > > It's awkward to start a sentence with a lower case letter. How about > rephrasing this paragraph and the following one as: > > Using bool as the return type of a function or as a variable is always > fine when appropriate. It often improves readability and is a better option > than int for storing boolean values. Using bool in data structures is > more debatable; its size and alignment can vary between architectures. This is more concise, but I think if the coding style is not going to give a concrete advise then it should at least provide some general information so the reader can try and make an informed choice. That is why I had it expand on some of the rationals a little bit, along with a concrete direction to not use bool in the cases Linus specifically called out. > > +Do not use bool if cache line layout or size of the value matters, its size > > +and alignment varies based on the compiled architecture. Structures that are > > +optimized for alignment and size should not use bool. > > + > > +If a structure has many true/false values, consider consolidating them into a > > +bitfield with 1 bit members, or using an appropriate fixed width type, such as > > +u8. JAson
