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Date: Fri, 03 Oct 2025 01:19:33 +0200
From: "Arnd Bergmann" <arnd@...db.de>
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Subject: Re: [PATCH v17 01/47] llist: move llist_{head,node} definition to types.h

On Thu, Oct 2, 2025, at 15:53, Mathieu Desnoyers wrote:
> On 2025-10-02 04:24, Greg KH wrote:
>> On Thu, Oct 02, 2025 at 05:12:01PM +0900, Byungchul Park wrote:
>>> llist_head and llist_node can be used by some other header files.  For
>>> example, dept for tracking dependencies uses llist in its header.  To
>>> avoid header dependency, move them to types.h.
>> 
>> If you need llist in your code, then include llist.h.  Don't force all
>> types.h users to do so as there is not a dependency in types.h for
>> llist.h.
>> 
>> This patch shouldn't be needed as you are hiding "header dependency" for
>> other files.
>
> I agree that moving this into a catch-all types.h is not what we should
> aim for.
>
> However, it's a good practice to move the type declarations to a
> separate header file, so code that only cares about type and not
> implementation of static inline functions can include just that.
>
> Perhaps we can move struct llist_head and struct llist_node to a new
> include/linux/llist_types.h instead ?

We have around a dozen types of linked lists, and the most common
two of them are currently defined in linux/types.h, while the
rest of them are each defined in the same header as the inteface
definition.

Duplicating each of those headers by splitting out the trivial
type definition doesn't quite seem right either, as we'd end
up with even more headers that have to be included indirectly
in each compilation unit.

Maybe a shared linux/list_types.h would work, to specifically
contain all the list_head variants that are meant to be included
in larger structures?

    Arnd

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