On 22-Dec-18 01:52, Jason Gunthorpe wrote: > On Thu, Dec 20, 2018 at 09:12:43PM -0800, Joe Perches wrote: >> Care to submit a coding_style.rst patch or >> improve the one below this? > > I took yours and revised it a little bit. I spent some time looking at > assembly and decided to drop the performance note, the number of cases > that run into overhead seems pretty small and probably already > requires !! to be correct. There is also an equally unlikely gain, ie > 'if (a & b)' optimizes a tiny bit better for bool types. > > I also added a small intro on bool, as I know some people are > unfamiliar with C11 _Bool and might think bool is just '#define bool > u8' > > (for those added to the cc) I'm looking at cases, like the patch that > spawned this, where the struct has a single bool and no performance > considerations. As CH said, seeing that get converted to int due to > checkpatch is worse than having used bool. Using u8 won't make this > struct smaller or faster. > > Cheers, > Jason > > From c5e2c887f6326e1c4369876f39996417da5e90cc Mon Sep 17 00:00:00 2001 > From: Jason Gunthorpe <jgg@xxxxxxxxxxxx> > Date: Fri, 21 Dec 2018 16:29:22 -0700 > Subject: [PATCH] coding-style: Clarify the expectations around bool > > There has been some confusion since checkpatch started warning about bool > use in structures, and people have been avoiding using it. > > Many people feel there is still a legitimate place for bool in structures, > so provide some guidance on bool usage derived from the entire thread that > spawned the checkpatch warning. Since a "Using bool" section is added, perhaps it's worth documenting the bool usage as a function parameter [1]? [1] https://www.spinics.net/lists/linux-rdma/msg72336.html > > Link: https://lkml.kernel.org/r/CA+55aFwVZk1OfB9T2v014PTAKFhtVan_Zj2dOjnCy3x6E4UJfA@xxxxxxxxxxxxxx > Signed-off-by: Joe Perches <joe@xxxxxxxxxxx> > Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx> > --- > Documentation/process/coding-style.rst | 33 ++++++++++++++++++++++---- > 1 file changed, 29 insertions(+), 4 deletions(-) > > diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst > index 4e7c0a1c427a9a..efdb1d32035fe1 100644 > --- a/Documentation/process/coding-style.rst > +++ b/Documentation/process/coding-style.rst > @@ -918,7 +918,32 @@ result. Typical examples would be functions that return pointers; they use > NULL or the ERR_PTR mechanism to report failure. > > > -17) Don't re-invent the kernel macros > +17) Using bool > +-------------- > + > +The Linux kernel uses the C11 standard for the 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 labels should be used instead > +of 0 and 1. > + > +bool function return types, arguments 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. > + > +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. > + > +Otherwise limited use of bool in structures does improve readability. > + > +18) Don't re-invent the kernel macros > ------------------------------------- > > The header file include/linux/kernel.h contains a number of macros that > @@ -941,7 +966,7 @@ need them. Feel free to peruse that header file to see what else is already > defined that you shouldn't reproduce in your code. > > > -18) Editor modelines and other cruft > +19) Editor modelines and other cruft > ------------------------------------ > > Some editors can interpret configuration information embedded in source files, > @@ -975,7 +1000,7 @@ own custom mode, or may have some other magic method for making indentation > work correctly. > > > -19) Inline assembly > +20) Inline assembly > ------------------- > > In architecture-specific code, you may need to use inline assembly to interface > @@ -1007,7 +1032,7 @@ the next instruction in the assembly output: > : /* outputs */ : /* inputs */ : /* clobbers */); > > > -20) Conditional Compilation > +21) Conditional Compilation > --------------------------- > > Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c >
