BlueZ coding style🔗
Every project has its coding style, and BlueZ is not an exception. This document describes the preferred coding style for BlueZ code, in order to keep some level of consistency among developers so that code can be easily understood and maintained.
First of all, BlueZ coding style must follow every rule for Linux kernel
(https://www.kernel.org/doc/Documentation/process/coding-style.rst). There also
exists a tool named checkpatch.pl to help you check the compliance with it.
Just type checkpatch.pl --no-tree patch_name to check your patch. In theory,
you need to clean up all the warnings and errors except this one: ERROR:
Missing Signed-off-by: line(s). BlueZ does not used Signed-off-by lines, so
including them is actually an error. In certain circumstances one can ignore
the 80 character per line limit. This is generally only allowed if the
alternative would make the code even less readable.
Besides the kernel coding style above, BlueZ has special flavors for its own.
Some of them are mandatory (marked as M), while some others are optional
(marked as O), but generally preferred.
M1: Blank line before and after an if/while/do/for statement🔗
There should be a blank line before if statement unless the if is nested and
not preceded by an expression or variable declaration.
Example: 1)
a = 1;
if (b) { // wrong
a = 1
if (b) {
}
a = 2; // wrong
if (a) {
if (b) // correct
b = 2;
if (a) { // correct
}
b = 3;
The only exception to this rule applies when a variable is being checked for errors as such:
err = stat(filename, &st);
if (err || !S_ISDIR(st.st_mode))
return;
M2: Multiple line comment🔗
If your comment has more than one line, please start it from the second line.
Example:
/*
* first line comment // correct
* ...
* last line comment
*/
M3: Space before and after operator🔗
There should be a space before and after each operator.
Example:
a + b; // correct
M4: Wrap long lines🔗
If your condition in if, while, for statement or a function declaration is too
long to fit in one line, the new line needs to be indented not aligned with the
body.
Example: 1)
if ((adapter->supported_settings & MGMT_SETTING_SSP) &&
!(adapter->current_settings & MGMT_SETTING_SSP)) // wrong
if ((adapter->supported_settings & MGMT_SETTING_SSP) &&
!(adapter->current_settings & MGMT_SETTING_SSP))
void btd_adapter_register_pin_cb(struct btd_adapter *adapter,
btd_adapter_pin_cb_t cb) // wrong
void btd_adapter_register_pin_cb(struct btd_adapter *adapter,
btd_adapter_pin_cb_t cb)
The referred style for line wrapping is to indent as far as possible to the right without hitting the 80 columns limit.
M5: Space when doing type casting🔗
There should be a space between new type and variable.
Example: 1)
a = (int *)b; // wrong
a = (int *) b; // correct
M6: Don’t initialize variable unnecessarily🔗
When declaring a variable, try not to initialize it unless necessary.
Example:
int i = 1; // wrong
for (i = 0; i < 3; i++) {
}
M7: Follow the order of include header elements🔗
When writing an include header the various elements should be in the following order:
#include’sforward declarations
#define’senum’stypedef’sfunction declarations and inline function definitions
M8: Internal headers must not use include guards🔗
Any time when creating a new header file with non-public API, that header must not contain include guards.
M9: Naming of enums🔗
Enums must have a descriptive name. The enum type should be small caps and
it should not be typedef’ed. Enum contents should be in CAPITAL letters and
prefixed by the enum type name.
Example:
enum animal_type {
ANIMAL_TYPE_FOUR_LEGS,
ANIMAL_TYPE_EIGHT_LEGS,
ANIMAL_TYPE_TWO_LEGS,
};
If the enum contents have values (e.g. from specification) the formatting should be as follows:
enum animal_type {
ANIMAL_TYPE_FOUR_LEGS = 4,
ANIMAL_TYPE_EIGHT_LEGS = 8,
ANIMAL_TYPE_TWO_LEGS = 2,
};
M10: Enum as switch variable🔗
If the variable of a switch is an enum, you must include all values in
switch body even if providing default. This is enforced by compiler option
enabling extra warning in such case. The reason for this is to ensure that if
later on the enum is modified and one forget to change the switch accordingly, the
compiler will complain the new added type hasn’t been handled.
Example:
enum animal_type {
ANIMAL_TYPE_FOUR_LEGS = 4,
ANIMAL_TYPE_EIGHT_LEGS = 8,
ANIMAL_TYPE_TWO_LEGS = 2,
};
enum animal_type t;
switch (t) { // OK
case ANIMAL_TYPE_FOUR_LEGS:
...
break;
case ANIMAL_TYPE_EIGHT_LEGS:
...
break;
case ANIMAL_TYPE_TWO_LEGS:
...
break;
default:
break;
}
switch (t) { // Wrong
case ANIMAL_TYPE_FOUR_LEGS:
...
break;
case ANIMAL_TYPE_TWO_LEGS:
...
break;
default:
break;
}
However if the enum comes from an external header file outside BlueZ, such as Android headers, we cannot make any assumption of how the enum is defined and this rule might not apply.
M11: Always use parenthesis with sizeof🔗
The expression argument to the sizeof operator should always be in
parenthesis, too.
Example: 1)
memset(stuff, 0, sizeof(*stuff));
memset(stuff, 0, sizeof *stuff); // Wrong
M12: Use void if function has no parameters🔗
A function with no parameters must use void in the parameter list.
Example: 1)
void foo(void)
{
}
void foo() // Wrong
{
}
O1: Try to avoid complex if body🔗
It’s better not to have a complicated statement for if. You may judge its
contrary condition and return, break, continue or goto as soon
as possible.
Example:
if (device) { // worse
memset(&eir_data, 0, sizeof(eir_data));
if (eir_len > 0)
eir_parse(&eir_data, ev->eir, eir_len);
...
} else {
error("Unable to get device object for %s", addr);
return;
}
if (!device) {
error("Unable to get device object for %s", addr);
return;
}
memset(&eir_data, 0, sizeof(eir_data));
if (eir_len > 0)
eir_parse(&eir_data, ev->eir, eir_len);
...