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authorLennart Poettering <lennart@poettering.net>2013-12-09 22:51:35 +0100
committerLennart Poettering <lennart@poettering.net>2013-12-09 23:04:05 +0100
commitd3a485135a98184cba28992752834a1bb4769003 (patch)
tree5a19c78c458b45acda20f5760eadeaebf83d2166 /CODING_STYLE
parent171754aa4ae37a6ab626878256f7b664da78ef55 (diff)
extend CODING_STYLE document a bit
Diffstat (limited to 'CODING_STYLE')
-rw-r--r--CODING_STYLE80
1 files changed, 63 insertions, 17 deletions
diff --git a/CODING_STYLE b/CODING_STYLE
index c5f1e2e6c9..996897bcde 100644
--- a/CODING_STYLE
+++ b/CODING_STYLE
@@ -4,7 +4,8 @@
- Variables and functions *must* be static, unless they have a
prototype, and are supposed to be exported.
-- structs in MixedCase, variables + functions in lower_case
+- 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
@@ -22,30 +23,35 @@
more than one cause, it *really* should have "int" as return value
for the error code.
-- Don't bother with error checking if writing to stdout/stderr worked.
+- 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.
+ 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.
+ "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
- 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, due to risk of
- deadlocks
+- 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 result in strings to be truncated. Often it is nicer to
- use dynamic memory, or alloca(). 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. Or in other words, if you use "char buf[256]" then
- you are likely doing something wrong!
+ 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.
@@ -113,11 +119,51 @@
}
- 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.
+ 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, but nothing else.
+ 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.
+
+- 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.
+
+- 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.