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Date: Thu, 23 May 2024 17:44:35 +0200
From: Christoph Hellwig <hch@lst.de>
To: Mike Snitzer <snitzer@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@lst.de>,
	axboe@kernel.dk, dm-devel@lists.linux.dev,
	linux-block@vger.kernel.org, Marco Patalano <mpatalan@redhat.com>,
	Ewan Milne <emilne@redhat.com>, linux-raid@vger.kernel.org
Subject: Re: [PATCH for-6.10-rc1] block: fix blk_validate_limits() to
 properly handle stacked devices
Message-ID: <20240523154435.GA1783@lst.de>
References: <20240522025117.75568-1-snitzer@kernel.org> <20240522142458.GB7502@lst.de> <Zk4h-6f2M0XmraJV@kernel.org> <Zk6haNVa5JXxlOf1@fedora> <Zk9i7V2GRoHxBPRu@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, May 23, 2024 at 11:38:21AM -0400, Mike Snitzer wrote:
> Sure, we could elevate it to blk_validate_limits (and callers) but
> adding a 'stacking' parameter is more intrusive on an API level.
> 
> Best to just update blk_set_stacking_limits() to set a new 'stacking'
> flag in struct queue_limits, and update blk_stack_limits() to stack
> that flag up.
> 
> I've verified this commit to work and have staged it in linux-next via
> linux-dm.git's 'for-next', see:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=cedc03d697ff255dd5b600146521434e2e921815
> 
> Jens (and obviously: Christoph, Ming and others), I'm happy to send
> this to Linus tomorrow morning if you could please provide your
> Reviewed-by or Acked-by.  I'd prefer to keep the intermediate DM fix
> just to "show the work and testing".

A stacking flag in the limits is fundamentally wrong, please don't
do this.