linux-kernel - RE: [RFC PATCH 1/2] add list_for_each_entry

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Date:   Sat, 21 Oct 2023 09:59:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Miklos Szeredi' <mszeredi@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Takashi Iwai <tiwai@...e.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Christian Brauner" <brauner@...nel.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: RE: [RFC PATCH 1/2] add list_for_each_entry_del()

From: Miklos Szeredi
> Sent: 20 October 2023 11:29
> 
> Add a new list iteration macro that always takes the first element of the
> list and removes it, until the list is empty.
...
> +/**
> + * list_for_each_entry_del - iterate list and remove elements
> + * @pos:	the type * to use as a loop cursor.
> + * @head:	the head for your list.
> + * @member:	the name of the list_head within the struct.
> + *
> + * Delete first element from list before the iteration.  Iterate until
> + * the list is empty.
> + */
> +#define list_for_each_entry_del(pos, head, member)			\
> +	while (!list_empty(head) &&					\
> +		({ pos = list_first_entry(head, typeof(*(pos)), member);\
> +		   list_del(&(pos)->member); 1; }))

That pattern is actually pretty obvious.
Add another wrapper and people end up having to read the
header to find out what it does.

I can't help feeling that if you look inside list_empty(),
list_first_entry() and list_del() there is a lot of
replicated code and tests.

Adding a list_del_first() function that returns the deleted
item or NULL to optimise it might make more sense.

	David

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