linux-kernel - Re: [PATCH v6 02/11] kbuild: Add list_size, list_at_index, list_for_each

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Message-ID: <Z1DjikoDzwIAID5T@bombadil.infradead.org>
Date: Wed, 4 Dec 2024 15:19:38 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Ole Schuerks <ole0811sch@...il.com>
Cc: linux-kbuild@...r.kernel.org, jude.gyimah@....de,
	thorsten.berger@....de, deltaone@...ian.org, jan.sollmann@....de,
	masahiroy@...nel.org, linux-kernel@...r.kernel.org,
	nathan@...nel.org, nicolas@...sle.eu
Subject: Re: [PATCH v6 02/11] kbuild: Add list_size, list_at_index,
 list_for_each_from

On Mon, Oct 28, 2024 at 04:49:40AM +0100, Ole Schuerks wrote:
> +/**
> + * list_size - counts the number of entries in a list
> + * @head: the list whose entries are counted
> + */
> +static inline size_t list_size(const struct list_head *head)
> +{
> +	size_t ret = 0;
> +
> +	for (struct list_head *curr = head->next; curr != head;
> +	     curr = curr->next)
> +		++ret;
> +
> +	return ret;

What's wrong with list_count_nodes()?

> @@ -310,6 +325,40 @@ static inline int list_empty(const struct list_head *head)
>  	     !list_entry_is_head(pos, head, member);			\
>  	     pos = n, n = list_next_entry(n, member))
>  
> +/**
> + * list_for_each_entry_from - iterate over list of given type starting at a given node
> + * @pos:	the type * to use as a loop cursor.
> + * @start:	the node to start iterating at
> + * @head:	the head for your list.
> + * @member:	the name of the list_head within the struct.
> + */
> +#define list_for_each_entry_from(pos, start, head, member)  \
> +	for (pos = list_entry(start, typeof(*pos), member); \
> +	     !list_entry_is_head(pos, head, member);        \
> +	     pos = list_next_entry(pos, member))

list_for_each_entry_from() exists on my tree on linux-next added
through commit e229c2fb3370a ("[LIST]: Introduce
list_for_each_entry_from") since v2.6.17, so since 2006.

> +/**
> + * list_at_index - retrieve the entry at index i in O(n)
> + * @i:		index of entry to retrieve.
> + * @head:	the head for your list.
> + * @type:	the type of the struct the entries are embedded in.
> + * @member:	the name of the list_head within the struct.
> + */
> +#define list_at_index(i, head, type, member)               \
> +	({                                                 \
> +		type *__pos;                               \
> +		size_t __counter = 0;                      \
> +		list_for_each_entry(__pos, head, member) { \
> +			if (__counter++ == i)              \
> +				break;                     \
> +			if (__pos->member.next == head) {  \
> +				__pos = NULL;              \
> +				break;                     \
> +			}                                  \
> +		}                                          \
> +		__pos;                                     \
> +	})
> +

Seems like the only thing being added. I'd just keep thsi internal
to your code for now, and later if we really want we can add this
as a generic helper. If you really want this on list.h I'd recommend
to find a few users of this already in kernel and generalize the common
thing to use it first and add it that way. Then you separate *that*
patches series from this one, and address that first, and address
the addition then as a seprate patch series.

If you keep it to the tool itself, just change the namespace to be not
be as generically named of course.

  Luis