X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=CODING_STYLE;h=996897bcde976479faf2845d6ca7a5f6f9930250;hp=1c6c12bc1e7410aedbefb3325bee21c1e7b95b8f;hb=9dddaedfcc70c6dc37ba6a48d1d8e27e12c0cb2e;hpb=f49f49ba133daf18c7690c733755eeaad075b858 diff --git a/CODING_STYLE b/CODING_STYLE index 1c6c12bc1..996897bcd 100644 --- a/CODING_STYLE +++ b/CODING_STYLE @@ -1,27 +1,169 @@ - 8ch indent, no tabs -- structs in MixedCase, variables, functions in lower_case +- Variables and functions *must* be static, unless they have a + prototype, and are supposed to be exported. -- the destructors always unregister the object from the next bigger +- structs in MixedCase (with exceptions, such as public API structs), + variables + functions in lower_case. + +- The destructors always unregister the object from the next bigger object, not the other way around -- to minimize strict aliasing violations we prefer unions over casting +- To minimize strict aliasing violations we prefer unions over casting -- for robustness reasons destructors should be able to destruct +- For robustness reasons destructors should be able to destruct half-initialized objects, too -- error codes are returned as negative Exxx. i.e. return -EINVAL. There +- Error codes are returned as negative Exxx. i.e. return -EINVAL. There are some exceptions: for constructors its is OK to return NULL on - OOM. For lookup functions NULL is fine too for "not found" + OOM. For lookup functions NULL is fine too for "not found". + + Be strict with this. When you write a function that can fail due to + more than one cause, it *really* should have "int" as return value + for the error code. + +- Don't bother with error checking whether writing to stdout/stderr + worked. + +- Do not log errors from "library" code, only do so from "main + program" code. (With one exception: it's OK to log with DEBUG level + from any code, with the exception of maybe inner loops). + +- Always check OOM. There's no excuse. In program code you can use + "log_oom()" for then printing a short message, but not in "library" code. - Do not issue NSS requests (that includes user name and host name - lookups) from the main daemon as this might trigger deadlocks when - we those lookups involve synchronously talking to services that we - would need to start up + lookups) from PID 1 as this might trigger deadlocks when those + lookups involve synchronously talking to services that we would need + to start up + +- Don't synchronously talk to any other service from PID 1, due to + risk of deadlocks + +- Avoid fixed sized string buffers, unless you really know the maximum + size and that maximum size is small. They are a source of errors, + since they possibly result in truncated strings. Often it is nicer + to use dynamic memory, alloca() or VLAs. If you do allocate fixed + size strings on the stack, then it's probably only OK if you either + use a maximum size such as LINE_MAX, or count in detail the maximum + size a string can have. (DECIMAL_STR_MAX and DECIMAL_STR_WIDTH + macros are your friends for this!) + + Or in other words, if you use "char buf[256]" then you are likely + doing something wrong! + +- Stay uniform. For example, always use "usec_t" for time + values. Don't usec mix msec, and usec and whatnot. + +- Make use of _cleanup_free_ and friends. It makes your code much + nicer to read! + +- Be exceptionally careful when formatting and parsing floating point + numbers. Their syntax is locale dependent (i.e. "5.000" in en_US is + generally understood as 5, while on de_DE as 5000.). + +- Try to use this: + + void foo() { + } + + instead of this: + + void foo() + { + } + + But it's OK if you don't. + +- Don't write "foo ()", write "foo()". + +- Please use streq() and strneq() instead of strcmp(), strncmp() where applicable. + +- Please do not allocate variables on the stack in the middle of code, + even if C99 allows it. Wrong: + + { + a = 5; + int b; + b = a; + } + + Right: + + { + int b; + a = 5; + b = a; + } + +- Unless you allocate an array, "double" is always the better choice + than "float". Processors speak "double" natively anyway, so this is + no speed benefit, and on calls like printf() "float"s get upgraded + to "double"s anyway, so there is no point. + +- Don't invoke functions when you allocate variables on the stack. Wrong: + + { + int a = foobar(); + uint64_t x = 7; + } + + Right: + + { + int a; + uint64_t x = 7; + + a = foobar(); + } + +- Use "goto" for cleaning up, and only use it for that. i.e. you may + only jump to the end of a function, and little else. Never jump + backwards! + +- Think about the types you use. If a value cannot sensibly be + negative don't use "int", but use "unsigned". + +- Don't use types like "short". They *never* make sense. Use ints, + longs, long longs, all in unsigned+signed fashion, and the fixed + size types uint32_t and so on, as well as size_t but nothing else. + +- Public API calls (i.e. functions exported by our shared libraries) + must be marked "_public_" and need to be prefixed with "sd_". No + other functions should be prefixed like that. + +- In public API calls you *must* validate all your input arguments for + programming error with assert_return() and return a sensible return + code. In all other calls it is recommended to check for programming + errors with a more brutal assert(). We are more forgiving to public + users then for ourselves! Note that assert() and assert_return() + really only should be used for detecting programming errors, not for + runtime errors. assert() and assert_return() by usage of _likely_() + inform the compiler that he shouldn't expect these checks to fail, + and they inform fellow programmers about the expected validity and + range of parameters. + +- Never use strtol(), atoi() and similar calls. Use safe_atoli(), + safe_atou32() and suchlike instead. They are much nicer to use in + most cases and correctly check for parsing errors. -- Do not access any directories outside of /etc/, /dev, /lib from the - init daemon to avoid deadlocks with the automounter +- For every function you add, think about whether it is a "logging" + function or a "non-logging" function. "Logging" functions do logging + on their own, "non-logging" function never log on their own and + expect their callers to log. All functions in "library" code, + i.e. in src/shared/ and suchlike must be "non-logging". Everytime a + "logging" function calls a "non-logging" function it should log + about the resulting errors. If a "logging" function calls another + "logging" function, then it should not generate log messages, so + that log messages are not generated twice for the same errors. -- Don't synchronously talk to any other service, due to risk of - deadlocks +- Avoid static variables, except for caches and very few other + cases. Think about thread-safety! While most of our code is never + used in threaded environments at least the library code should make + sure it works correctly in them. Instead of doing a lot of locking + for that we tend to prefer using TLS to do per-thread caching (which + only works for small, fixed-size cache objects), or we disable + caching for any thread that is not the main thread. Use + is_main_thread() to detect whether the calling thread is the main + thread.