From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/9] MD: add a new disk role to present cache device
Date: Tue, 4 Aug 2015 07:28:24 -0700
Message-ID: <20150804142824.GA8204@infradead.org>
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>  		case 0xfffe: /* faulty */
>  			set_bit(Faulty, &rdev->flags);
>  			break;
> +		case 0xfffd: /* cache device */

Any chance to get constants for these magic numbers as an additional
prep patch?

Also I don't really think that adding the role without the actual
implementation is that useful.