CODING_STYLE

   1
   2 - 8ch indent, no tabs
   3
   4 - Variables and functions *must* be static, unless they have a
   5   protoype, and are supposed to be exported.
   6
   7 - structs in MixedCase, variables + functions in lower_case
   8
   9 - The destructors always unregister the object from the next bigger
  10   object, not the other way around
  11
  12 - To minimize strict aliasing violations we prefer unions over casting
  13
  14 - For robustness reasons destructors should be able to destruct
  15   half-initialized objects, too
  16
  17 - Error codes are returned as negative Exxx. i.e. return -EINVAL. There
  18   are some exceptions: for constructors its is OK to return NULL on
  19   OOM. For lookup functions NULL is fine too for "not found".
  20
  21   Be strict with this. When you write a function that can fail due to
  22   more than one cause, it *really* should have "int" as return value
  23   for the error code.
  24
  25 - Don't bother with error checking if writing to stdout/stderr worked.
  26
  27 - Do not log errors from "library" code, only do so from "main
  28   program" code.
  29
  30 - Always check OOM. There's no excuse. In program code you can use
  31   "log_oom()" for then printing a short message.
  32
  33 - Do not issue NSS requests (that includes user name and host name
  34   lookups) from the main daemon as this might trigger deadlocks when
  35   those lookups involve synchronously talking to services that we
  36   would need to start up
  37
  38 - Don't synchronously talk to any other service, due to risk of
  39   deadlocks
  40
  41 - Avoid fixed sized string buffers, unless you really know the maximum
  42   size and that maximum size is small. They are a source of errors,
  43   since they result in strings to be truncated. Often it is nicer to
  44   use dynamic memory, or alloca(). If you do allocate fixed size
  45   strings on the stack, then it's probably only OK if you either use a
  46   maximum size such as LINE_MAX, or count in detail the maximum size a
  47   string can have. Or in other words, if you use "char buf[256]" then
  48   you are likely doing something wrong!
  49
  50 - Stay uniform. For example, always use "usec_t" for time
  51   values. Don't usec mix msec, and usec and whatnot.
  52
  53 - Make use of _cleanup_free_ and friends. It makes your code much
  54   nicer to read!
  55
  56 - Be exceptionally careful when formatting and parsing floating point
  57   numbers. Their syntax is locale dependent (i.e. "5.000" in en_US is
  58   generally understood as 5, while on de_DE as 5000.).
  59
  60 - Try to use this:
  61
  62       void foo() {
  63       }
  64
  65   instead of this:
  66
  67       void foo()
  68       {
  69       }
  70
  71   But it's OK if you don't.
  72
  73 - Don't write "foo ()", write "foo()".
  74
  75 - Please use streq() and strneq() instead of strcmp(), strncmp() where applicable.
  76
  77 - Please do not allocate variables on the stack in the middle of code,
  78   even if C99 allows it. Wrong:
  79
  80   {
  81           a = 5;
  82           int b;
  83           b = a;
  84   }
  85
  86   Right:
  87
  88   {
  89           int b;
  90           a = 5;
  91           b = a;
  92   }
  93
  94 - Unless you allocate an array, "double" is always the better choice
  95   than "float". Processors speak "double" natively anyway, so this is
  96   no speed benefit, and on calls like printf() "float"s get upgraded
  97   to "double"s anyway, so there is no point.
  98
  99 - Don't invoke functions when you allocate variables on the stack. Wrong:
 100
 101   {
 102           int a = foobar();
 103           uint64_t x = 7;
 104   }
 105
 106   Right:
 107
 108   {
 109           int a;
 110           uint64_t x = 7;
 111
 112           a = foobar();
 113   }
 114
 115 - Use "goto" for cleaning up, and only use it for that. i.e. you may
 116   only jump to the end of a function, and little else.
 117
 118 - Think about the types you use. If a value cannot sensibly be
 119   negative don't use "int", but use "unsigned".
 120
 121 - Don't use types like "short". They *never* make sense. Use ints,
 122   longs, long longs, all in unsigned+signed fashion, and the fixed
 123   size types uint32_t and so on, but nothing else.