linux-kernel - Re: [PATCH v3 3/3] bootconfig: Free xbc_data in xbc_destroy

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Message-ID: <20210915102354.2841798d@oasis.local.home>
Date:   Wed, 15 Sep 2021 10:23:54 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, Linux-MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v3 3/3] bootconfig: Free xbc_data in xbc_destroy_all()

On Wed, 15 Sep 2021 22:19:52 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> @@ -810,6 +811,8 @@ void __init xbc_destroy_all(void)
>   * In error cases, @emsg will be updated with an error message and
>   * @epos will be updated with the error position which is the byte offset
>   * of @buf. If the error is not a parser error, @epos will be -1.
> + * Note that the @buf ownership is transferred, so it will be freed
> + * in xbc_destroy_all().
>   */
>  int __init xbc_init(char *buf, const char **emsg, int *epos)
>  {

I hate this "ownership transfer". Looking at the use case here:

init/main.c:

	copy = memblock_alloc(size + 1, SMP_CACHE_BYTES);
	if (!copy) {
		pr_err("Failed to allocate memory for bootconfig\n");
		return;
	}

	memcpy(copy, data, size);
	copy[size] = '\0';

	ret = xbc_init(copy, &msg, &pos);
	if (ret < 0) {

Instead of having xbc_init() return the node count on success, how about
having it allocate the buffer to use and then return it?

That is, move the:

	copy = memblock_alloc(size + 1, SMP_CACHE_BYTES);
	if (!copy) {
		pr_err("Failed to allocate memory for bootconfig\n");
		return;
	}

	memcpy(copy, data, size);
	copy[size] = '\0';

into xbc_init(), and have data, and size be passed to it.

Then, have it return the pointer of "copy" or NULL on error?

This will keep the semantics of xbc_* owning the buffer that gets
freed by the destroy.

The xbc_init() could also do the pr_info() that prints the bytes and
node count. There's no other reason to pass that node count to the
caller, is there?

-- Steve