DEFINE_FREE/CLASS && code readability (Was: [PATCH v2 2/6] Provide __free(argv) for argv_split() users)

[Oleg Nesterov]

Masami,

Sorry for abusing this thread. Your patches look fine to me, it is not
that I suggest to change them. I will use your patch as an example for
off-topic discussion.

On 01/05, Masami Hiramatsu (Google) wrote:
>
> +DEFINE_FREE(argv, char **, if (!IS_ERR_OR_NULL(_T)) argv_free(_T))

(IS_ERR looks unneeded but this is cosmetic).

OK, so it can be used as

	void func(void)
	{
		char **argv __free(argv) = argv_split(...);
		do_something(argv);
		return;
	}

And I cry every time when I read the code like this ;)

Because, to understand this code, I need to do the "nontrivial" grep to find
"DEFINE_FREE(argv,".

Perhaps we can establish a simple rule that every DEFINE_FREE() or DEFINE_CLASS()
should add another #define? I mean something like


	DEFINE_FREE(argv, char **, if (!IS_ERR_OR_NULL(_T)) argv_free(_T))
	#define __FREE_ARGV	__free(argv)
	
	void func(void)
	{
		char **argv __FREE_ARGV = argv_split(...);
		do_something(argv);
		return;
	}

This way I can press Ctrl-] and see what the cleanup code actually does.
Can save a second or two. Important when you try to read the code you are
not familiar with.

Same for DEFINE_CLASS. For example,

	int ksys_fchown(unsigned int fd, uid_t user, gid_t group)
	{
		CLASS(fd, f)(fd);

		if (fd_empty(f))
			return -EBADF;

		return vfs_fchown(fd_file(f), user, group);
	}

If you are not familiar with this code, it looks mysterious until you find
DEFINE_CLASS(fd, ...) in include/linux/file.h.

Oleg.