-- 8ch indent, no tabs
+- 8ch indent, no tabs, except for files in man/ which are 2ch indent,
+ and still no tabs
+
+- We prefer /* comments */ over // comments, please. This is not C++, after
+ all. (Yes we know that C99 supports both kinds of comments, but still,
+ please!)
- Don't break code lines too eagerly. We do *not* force line breaks at
80ch, all of today's screens should be much larger than that. But
no speed benefit, and on calls like printf() "float"s get promoted
to "double"s anyway, so there is no point.
-- Do not invoke functions when you allocate variables on the stack. Wrong:
+- Do not mix function invocations with variable definitions in one
+ line. Wrong:
{
int a = foobar();
- Do not 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.
+ size types uint32_t and so on, as well as size_t, but nothing
+ else. Do not use kernel types like u32 and so on, leave that to the
+ kernel.
- Public API calls (i.e. functions exported by our shared libraries)
must be marked "_public_" and need to be prefixed with "sd_". No
is_main_thread() to detect whether the calling thread is the main
thread.
-- Option parsing:
+- Command line option parsing:
- Do not print full help() on error, be specific about the error.
- Do not print messages to stdout on error.
- Do not POSIX_ME_HARDER unless necessary, i.e. avoid "+" in option string.
+
+- Do not write functions that clobber call-by-reference variables on
+ failure. Use temporary variables for these cases and change the
+ passed in variables only on success.
+
+- When you allocate a file descriptor, it should be made O_CLOEXEC
+ right from the beginning, as none of our files should leak to forked
+ binaries by default. Hence, whenever you open a file, O_CLOEXEC must
+ be specified, right from the beginning. This also applies to
+ sockets. Effectively this means that all invocations to:
+
+ a) open() must get O_CLOEXEC passed
+ b) socket() and socketpair() must get SOCK_CLOEXEC passed
+ c) recvmsg() must get MSG_CMSG_CLOEXEC set
+ d) F_DUPFD_CLOEXEC should be used instead of F_DUPFD, and so on
+
+- We never use the POSIX version of basename() (which glibc defines it in
+ libgen.h), only the GNU version (which glibc defines in string.h).
+ The only reason to include libgen.h is because dirname()
+ is needed. Everytime you need that please immediately undefine
+ basename(), and add a comment about it, so that no code ever ends up
+ using the POSIX version!
+
+- Use the bool type for booleans, not integers. One exception: in public
+ headers (i.e those in src/systemd/sd-*.h) use integers after all, as "bool"
+ is C99 and in our public APIs we try to stick to C89 (with a few extension).
+
+- When you invoke certain calls like unlink(), or mkdir_p() and you
+ know it is safe to ignore the error it might return (because a later
+ call would detect the failure anyway, or because the error is in an
+ error path and you thus couldn't do anything about it anyway), then
+ make this clear by casting the invocation explicitly to (void). Code
+ checks like Coverity understand that, and will not complain about
+ ignored error codes. Hence, please use this:
+
+ (void) unlink("/foo/bar/baz");
+
+ instead of just this:
+
+ unlink("/foo/bar/baz");
+
+- Don't invoke exit(), ever. It is not replacement for proper error
+ handling. Please escalate errors up your call chain, and use normal
+ "return" to exit from the main function of a process. If you
+ fork()ed off a child process, please use _exit() instead of exit(),
+ so that the exit handlers are not run.
+
+- Please never use dup(). Use fcntl(fd, F_DUPFD_CLOEXEC, 3)
+ instead. For two reason: first, you want O_CLOEXEC set on the new fd
+ (see above). Second, dup() will happily duplicate your fd as 0, 1,
+ 2, i.e. stdin, stdout, stderr, should those fds be closed. Given the
+ special semantics of those fds, it's probably a good idea to avoid
+ them. F_DUPFD_CLOEXEC with "3" as parameter avoids them.
+
+- When you define a destructor or unref() call for an object, please
+ accept a NULL object and simply treat this as NOP. This is similar
+ to how libc free() works, which accepts NULL pointers and becomes a
+ NOP for them. By following this scheme a lot of if checks can be
+ removed before invoking your destructor, which makes the code
+ substantially more readable and robust.
+
+- Related to this: when you define a destructor or unref() call for an
+ object, please make it return the same type it takes and always
+ return NULL from it. This allows writing code like this:
+
+ p = foobar_unref(p);
+
+ which will always work regardless if p is initialized or not, and
+ guarantees that p is NULL afterwards, all in just one line.
+
+- Use alloca(), but never forget that it is not OK to invoke alloca()
+ within a loop or within function call parameters. alloca() memory is
+ released at the end of a function, and not at the end of a {}
+ block. Thus, if you invoke it in a loop, you keep increasing the
+ stack pointer without ever releasing memory again. (VLAs have better
+ behaviour in this case, so consider using them as an alternative.)
+ Regarding not using alloca() within function parameters, see the
+ BUGS section of the alloca(3) man page.
+
+- Use memzero() or even better zero() instead of memset(..., 0, ...)
+
+- Instead of using memzero()/memset() to initialize structs allocated
+ on the stack, please try to use c99 structure initializers. It's
+ short, prettier and actually even faster at execution. Hence:
+
+ struct foobar t = {
+ .foo = 7,
+ .bar = "bazz",
+ };
+
+ instead of:
+
+ struct foobar t;
+ zero(t);
+ t.foo = 7;
+ t.bar = "bazz";
+
+- When returning a return code from main(), please preferably use
+ EXIT_FAILURE and EXIT_SUCCESS as defined by libc.
+
+- The order in which header files are included doesn't matter too
+ much. However, please try to include the headers of external
+ libraries first (these are all headers enclosed in <>), followed by
+ the headers of our own public headers (these are all headers
+ starting with "sd-"), internal utility libraries from src/shared/,
+ followed by the headers of the specific component. Or in other
+ words:
+
+ #include <stdio.h>
+ #include "sd-daemon.h"
+ #include "util.h"
+ #include "frobnicator.h"
+
+ Where stdio.h is a public glibc API, sd-daemon.h is a public API of
+ our own, util.h is a utility library header from src/shared, and
+ frobnicator.h is an placeholder name for any systemd component. The
+ benefit of following this ordering is that more local definitions
+ are always defined after more global ones. Thus, our local
+ definitions will never "leak" into the global header files, possibly
+ altering their effect due to #ifdeffery.
+
+- To implement an endless loop, use "for (;;)" rather than "while
+ (1)". The latter is a bit ugly anyway, since you probably really
+ meant "while (true)"... To avoid the discussion what the right
+ always-true expression for an infinite while() loop is our
+ recommendation is to simply write it without any such expression by
+ using "for (;;)".
~ianmdlvl / elogind.git / blobdiff