linux-kernel - Re: [PATCH v3 1/2] printk: console: Create console= parser that supports named options

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Message-ID: <ZD1f-1JjpihR1djd@chrisdown.name>
Date:   Mon, 17 Apr 2023 16:04:27 +0100
From:   Chris Down <chris@...isdown.name>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, kernel-team@...com
Subject: Re: [PATCH v3 1/2] printk: console: Create console= parser that
 supports named options

(To others on this thread wondering about this patchset, Petr and I have had 
some discussions offlist about v4 and it should be up soon.)

Petr Mladek writes:
>I thought a lot how to do it a clean way. IMHO, it would be great to
>parse everything at a single place but it might require updating
>all drivers. I am not sure if it is worth it.
>
>So, I suggest to do it another way. We could implement a generic
>function to find in the new key[:value] format. It would check
>if the given option (key) exists and read the optional value.
>
>The optional value would allow to define another new options
>that would not need any value, e.g. "kthread" or "atomic" that
>might be used in the upcoming code that allows to offload
>console handling to kthreads.

Any thoughts on something simple like this that takes advantage of memmove()? 
This should overcome the mmio/io concerns, and it's fairly simple.

---

static bool find_and_remove_console_option(char *buf, size_t size,
					   const char *wanted, char *options)
{
	bool found = false, first = true;
	char *item, *opt = options;

	while ((item = strsep(&opt, ","))) {
		char *key = item, *value;

		value = strchr(item, ':');
		if (value)
			*(value++) = '\0';

		if (strcmp(key, wanted) == 0) {
			found = true;
			if (value) {
				if (strlen(value) > size - 1) {
					pr_warn("Can't copy console option value for %s:%s: not enough space (%zu)\n",
						key, value, size);
					found = false;
				} else {
					strscpy(buf, value, size);
				}
			} else
				*buf = '\0';
		}

		if (!found && opt)
			*(opt - 1) = ',';
		if (!found && value)
			*(value - 1) = ':';
		if (!first)
			*(item - 1) = ',';

		if (found)
			break;

		first = false;
	}

	if (found) {
		if (opt)
			memmove(item, opt, strlen(opt) + 1);
		else if (first)
			*item = '\0';
		else
			*--item = '\0';
	}

	return found;
}