linux-kernel - Re: [PATCH v5 03/10] maple_tree: Introduce interfaces __mt_dup() and mtree

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Message-ID: <ZS1ESVpQ+vY0yDt4@casper.infradead.org>
Date:   Mon, 16 Oct 2023 15:10:17 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Peng Zhang <zhangpeng.00@...edance.com>
Cc:     Liam.Howlett@...cle.com, corbet@....net, akpm@...ux-foundation.org,
        brauner@...nel.org, surenb@...gle.com, michael.christie@...cle.com,
        mjguzik@...il.com, mathieu.desnoyers@...icios.com,
        npiggin@...il.com, peterz@...radead.org, oliver.sang@...el.com,
        mst@...hat.com, maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 03/10] maple_tree: Introduce interfaces __mt_dup() and
 mtree_dup()

On Mon, Oct 16, 2023 at 11:22:19AM +0800, Peng Zhang wrote:
> +++ b/lib/maple_tree.c
> @@ -4,6 +4,10 @@
>   * Copyright (c) 2018-2022 Oracle Corporation
>   * Authors: Liam R. Howlett <Liam.Howlett@...cle.com>
>   *	    Matthew Wilcox <willy@...radead.org>
> + *
> + * Algorithm for duplicating Maple Tree
> + * Copyright (c) 2023 ByteDance
> + * Author: Peng Zhang <zhangpeng.00@...edance.com>

You can't copyright an algorithm.  You can copyright the
_implementation_ of an algorithm.  You have a significant chunk of code
in this file, so adding your copyright is reasonable (although not
legally required, AIUI).  Just leave out this line:

+ * Algorithm for duplicating Maple Tree

> +/**
> + * __mt_dup(): Duplicate an entire maple tree
> + * @mt: The source maple tree
> + * @new: The new maple tree
> + * @gfp: The GFP_FLAGS to use for allocations
> + *
> + * This function duplicates a maple tree in Depth-First Search (DFS) pre-order
> + * traversal. It uses memcopy() to copy nodes in the source tree and allocate

memcpy()?

> +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> +{
> +	int ret = 0;
> +	MA_STATE(mas, mt, 0, 0);
> +	MA_STATE(new_mas, new, 0, 0);
> +
> +	mas_dup_build(&mas, &new_mas, gfp);
> +
> +	if (unlikely(mas_is_err(&mas))) {
> +		ret = xa_err(mas.node);
> +		if (ret == -ENOMEM)
> +			mas_dup_free(&new_mas);
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(__mt_dup);

Why does it need to be exported?