Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.32 as permitted sender) client-ip=23.128.96.32;
From:   David Laight <David.Laight@ACULAB.COM>
To:     'Miklos Szeredi' <mszeredi@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
        Takashi Iwai <tiwai@suse.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Christian Brauner" <brauner@kernel.org>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: RE: [RFC PATCH 1/2] add list_for_each_entry_del()
Thread-Topic: [RFC PATCH 1/2] add list_for_each_entry_del()
Thread-Index: AQHaA0BhVdxwGOC7H06bkVWqGZ+tgrBUAoSg
Date:   Sat, 21 Oct 2023 09:59:59 +0000
Message-ID: <3ab474953c734d0bbf0177bf5d208799@AcuMS.aculab.com>
References: <20231020102901.3354273-1-mszeredi@redhat.com>
 <20231020102901.3354273-2-mszeredi@redhat.com>
In-Reply-To: <20231020102901.3354273-2-mszeredi@redhat.com>
Accept-Language: en-GB, en-US
MIME-Version: 1.0
Content-Language: en-US
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Precedence: bulk

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

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)