linux-kernel - Re: [PATCH 2/6] list: add new MACROs to make iterator invisiable

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Message-ID: <YiqPmIdZ/RGiaOei@qmqm.qmqm.pl>
Date:   Fri, 11 Mar 2022 00:54:00 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Xiaomeng Tong <xiam0nd.tong@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/6] list: add new MACROs to make iterator invisiable

Hi Linus,

If the macro implementation doesn't have to be pretty, maybe it could go
a step further and remember the list_head's offset? That would look
something like following (expanding on your patch; not compile tested):

#define list_traversal_head(type,name,target_member) \
	union { \
		struct list_head name; \
		type *name##_traversal_type; \
		char (*name##_list_head_offset)[offsetof(type, target_member)];  \
	}

#define list_traversal_entry(ptr, head) \
	(typeof(*head##_traversal_type))((void *)ptr - sizeof(**head##_list_head_offset))

#define list_traversal_entry_head(ptr, head) \
	(struct list_head *)((void *)ptr + sizeof(**head##_list_head_offset))

#define list_traversal_entry_is_head(ptr, head) \
	(list_traversal_entry_head(ptr, head) == (head))

#define list_traversal_next_entry(ptr, head) \
	list_traversal_entry(list_traversal_entry_head(ptr, head)->next)

#define list_traverse(pos, head) \
	for (typeof(*head##_traversal_type) pos = list_traversal_entry((head)->next); \
		!list_traversal_entry_head(pos, head) == (head); \
		pos = list_traversal_next_entry(pos, head))

[Sorry for lack of citations - I found the thread via https://lwn.net/Articles/887097/]

-- 
Michał Mirosław