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

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Date:   Thu,  3 Mar 2022 11:31:22 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     james.bottomley@...senpartnership.com
Cc:     arnd@...db.de, gregkh@...uxfoundation.org, jakobkoschel@...il.com,
        jannh@...gle.com, keescook@...omium.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        torvalds@...ux-foundation.org, xiam0nd.tong@...il.com
Subject: Re: [PATCH 2/6] list: add new MACROs to make iterator invisiable outside the loop

On Wed, 02 Mar 2022 08:02:23 -0500, James Bottomley
<James.Bottomley@...senPartnership.com> wrote:
> pos shouldn't be an input to the macro since it's being declared inside
> it.  All that will do will set up confusion about the shadowing of pos.
> The macro should still work as
>
> #define list_for_each_entry_inside(type, head, member) \
>   ...
>
> For safety, you could
>
> #define POS __UNIQUE_ID(pos)
>
> and use POS as the loop variable .. you'll have to go through an
> intermediate macro to get it to be stable.  There are examples in
> linux/rcupdate.h

The outer "pos" variable is no longer needed and thus the declare
statement before the loop is removed, see the demostration in PATCH
3~6. Now, there is only one inner "pos" variable left. Thus, there
should be no such *shadow* problem.

Please remind me if i missed something, thanks.

--
Xiaomeng Tong