From mboxrd@z Thu Jan 1 00:00:00 1970 From: Federico Vaga Subject: Re: [PATCH v5] coding-style: Clarify the expectations around bool Date: Sun, 20 Jan 2019 09:36:43 +0100 Message-ID: <69366f385e6bdf23d67589850d98cf51@vaga.pv.it> References: <20190118225047.GH4759@ziepe.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190118225047.GH4759@ziepe.ca> Sender: linux-kernel-owner@vger.kernel.org To: Jason Gunthorpe Cc: Joe Perches , Gal Pressman , Bart Van Assche , Stephen Warren , Tariq Toukan , xavier.huwei@huawei.com, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, Doug Ledford , Stephen Warren , Christoph Hellwig , Andrew Morton , Linus Torvalds , linux-doc@vger.kernel.org, Jonathan Corbet , linux-kernel@vger.kernel.org List-Id: linux-rdma@vger.kernel.org On 2019-01-18 23:50, Jason Gunthorpe wrote: > 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. > > Link: > https://lkml.kernel.org/r/CA+55aFwVZk1OfB9T2v014PTAKFhtVan_Zj2dOjnCy3x6E4UJfA@mail.gmail.com > Signed-off-by: Joe Perches > Acked-by: Joe Perches > Reviewed-by: Bart Van Assche > Acked-by: Jani Nikula > Reviewed-by: Joey Pabalinas > Signed-off-by: Jason Gunthorpe Acked-by: Federico Vaga > --- > Documentation/process/coding-style.rst | 38 +++++++++++++++++++++++--- > scripts/checkpatch.pl | 13 --------- > 2 files changed, 34 insertions(+), 17 deletions(-) > > v5: > - Wording updates from JoeyP, MatthewW, FedericoV > > diff --git a/Documentation/process/coding-style.rst > b/Documentation/process/coding-style.rst > index b78dd680c03809..de889deaf29c42 100644 > --- a/Documentation/process/coding-style.rst > +++ b/Documentation/process/coding-style.rst > @@ -921,7 +921,37 @@ 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 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 1 and 0. > + > +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. > + > +Do not use bool if cache line layout or size of the value matters, as > 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. > + > +Similarly for function arguments, many true/false values can be > consolidated > +into a single bitwise 'flags' argument and 'flags' can often be a more > +readable alternative if the call-sites have naked true/false > constants. > + > +Otherwise limited use of bool in structures and arguments can improve > +readability. > + > +18) Don't re-invent the kernel macros > ------------------------------------- > > The header file include/linux/kernel.h contains a number of macros > that > @@ -944,7 +974,7 @@ 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, > @@ -978,7 +1008,7 @@ 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 > @@ -1010,7 +1040,7 @@ 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 > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl > index b737ca9d720441..d62abd032885a1 100755 > --- a/scripts/checkpatch.pl > +++ b/scripts/checkpatch.pl > @@ -6368,19 +6368,6 @@ sub process { > } > } > > -# check for bool bitfields > - if ($sline =~ /^.\s+bool\s*$Ident\s*:\s*\d+\s*;/) { > - WARN("BOOL_BITFIELD", > - "Avoid using bool as bitfield. Prefer bool bitfields as > unsigned int or u<8|16|32>\n" . $herecurr); > - } > - > -# check for bool use in .h files > - if ($realfile =~ /\.h$/ && > - $sline =~ /^.\s+bool\s*$Ident\s*(?::\s*d+\s*)?;/) { > - CHK("BOOL_MEMBER", > - "Avoid using bool structure members because of possible > alignment issues - see: https://lkml.org/lkml/2017/11/21/384\n" . > $herecurr); > - } > - > # check for semaphores initialized locked > if ($line =~ /^.\s*sema_init.+,\W?0\W?\)/) { > WARN("CONSIDER_COMPLETION", -- Federico Vaga http://www.federicovaga.it/