On 2019-01-11 00:48, 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_zj2dojncy3x6e4u...@mail.gmail.com
Signed-off-by: Joe Perches <j...@perches.com>
Acked-by: Joe Perches <j...@perches.com>
Reviewed-by: Bart Van Assche <bvanass...@acm.org>
Signed-off-by: Jason Gunthorpe <j...@mellanox.com>
---
Documentation/process/coding-style.rst | 38 +++++++++++++++++++++++---
scripts/checkpatch.pl | 13 ---------
2 files changed, 34 insertions(+), 17 deletions(-)
v4:
- Describe true/false as definitions [Joe]
- Use clearer language for the _Bool explanation [Bart]
- Delete the checkpatch tests [Joe]
diff --git a/Documentation/process/coding-style.rst
b/Documentation/process/coding-style.rst
index b78dd680c03809..db3e030d0df908 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 0 and 1.
A very minor thing. I would suggest to keep consistent, in the
statement, the mapping
between definitions ("true and false [...]") and their correspondent
integer values
("[...] instead of 1 and 0").
In few words, I propose to change "0 and 1" into "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, 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 a more
readable
+alternative if the call-sites have naked true/false constants.
Of course, English is not my primary language, but it looks to me that
here a "be"
is missing: "[...] and 'flags' can often a more readable alternative
[...]".
+
+Otherwise limited use of bool in structures and arguments can improve
+readability.
I'm going to update the Italian translations for this. Do you want me to
contribute
directly to this patch? Otherwise I will send a dedicated patch later
when this one
get accepted.
Thanks
+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/
