linux-kernel - Re: [PATCH 04/24] PCI: Add busn

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Message-ID: <CAErSpo7F4caRyFVjrQKoCZLMo-45Vy+oEr4fMUXLeMojpuDNag@mail.gmail.com>
Date:	Sun, 12 Feb 2012 16:11:48 -0800
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...el.com>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 04/24] PCI: Add busn_res operation functions

On Sun, Feb 12, 2012 at 4:03 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Sun, Feb 12, 2012 at 3:51 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>>
>>>>
>>>> I think it would be better to remove the bus resource from the tree,
>>>> change its "end," then re-insert it.
>>>
>>> how about parent buses that have extended top?
>>
>> I don't understand your question.  I assume you mean there's a case
>> where remove/update/reinsert doesn't work, but I don't see why that
>> would be a problem.  Can you show an example?
>
> I mean parent busn_res already had several level's children busn_res.
> and every level may have some siblings.
> before remove will need to record those resources, to later to put them back.
>
> that just increase not necessary complexity. because we already know
> those resource could be extended safely.

You're doing surgery on the middle of a relatively complicated data
structure.  Now readers of the code have to trust that not only does
kernel/resource.c work correctly, but they also have to examine this
PCI code to make sure that these alterations are safe.  I know this is
all crystal-clear in your mind, and no doubt it is correct right now,
but I don't think it is a reader-friendly approach.

But I don't expect to convince you, so I'll stop trying :)

Bjorn
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