Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756192Ab2HJBAx (ORCPT ); Thu, 9 Aug 2012 21:00:53 -0400 Received: from exout101.netflix.com ([69.53.237.162]:50414 "EHLO exout103.netflix.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751676Ab2HJBAv (ORCPT ); Thu, 9 Aug 2012 21:00:51 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024;d=netflix.com; h=from:to:cc:subject:date:message-id:references:in-reply-to :content-type:mime-version; b=hvNoYqpwpjPTS6NJ2T+LxLu9lK99+pKjvJeTRMVKbTqSWMiBcxVQwcUe16L03cJNnYuUJcfK PsiEfoB9snPNlw3+d8CzCS71JM/ohho64r6LxI0mkKyzgurhTIv0gJtokqf2+e7xLfckelBY VU0Rd9QrsuQgL4okNvcn7IMK2zY= From: Wesley Miaw To: Alasdair G Kergon CC: Milan Broz , Mikulas Patocka , device-mapper development , "msb@google.com" , "linux-kernel@vger.kernel.org" , =?Windows-1252?Q?Will_Drewry=99?= Subject: Re: [dm-devel] [PATCH v2 1/2] dm: verity support data device offset (Linux 3.4.7) Thread-Topic: [dm-devel] [PATCH v2 1/2] dm: verity support data device offset (Linux 3.4.7) Thread-Index: AQHNddNR+SZbnrO+/UG7B9aFuaaGnZdSsNmA Date: Fri, 10 Aug 2012 01:00:50 +0000 Message-ID: <6C715FBD-EDE6-44F4-A26F-9F49C861C827@netflix.com> References: <8893CF66-2E2C-4D8F-9239-E38BE55716AE@netflix.com> <5022CC99.30103@redhat.com> <0066B4B7-B0FA-4C7F-99C4-0AABB577382C@netflix.com> <20120809020419.GD23758@agk-dp.fab.redhat.com> In-Reply-To: <20120809020419.GD23758@agk-dp.fab.redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-originating-ip: [10.2.229.146] Content-Type: multipart/signed; boundary="Apple-Mail=_650297C4-27F9-4367-8D4A-7D72172190C4"; protocol="application/pgp-signature"; micalg=pgp-sha1 MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3023 Lines: 68 --Apple-Mail=_650297C4-27F9-4367-8D4A-7D72172190C4 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii On Aug 8, 2012, at 7:04 PM, Alasdair G Kergon wrote: >=20 > However, first you need to address the second part of Mikulas's email, > namely to make the case for these changes rather than making no kernel > changes and instead stacking the verity target over a linear target. >=20 > To put this another way, your patch offers an alternative way to do > something we think the existing kernel can already do, so you need to > advance some reasons why you believe the new alternative method is = worth > adding to the kernel and explain this in the patch header. I'm afraid for some reason I didn't get Mikulas's first email, only the = reply from Milan which must have been an incomplete quote of Mikulas's = text. For my part, I approached this as porting my existing code to the new = dm-verity implementation included in Linux 3.4. The previous code used a = data offset as this was convenient and directly supported the block = device image format I put together back then. However I can indeed accomplish what I need using linear, it's just a = bit more code. I am not able to measure any runtime performance = difference. The primary benefit I can see for is the reduced kernel = footprint if the linear target does not need to be included (and my = corresponding setup code is about 1/3 smaller). With my cross-compiled = kernel the savings is ~1KB; this is obviously a very small benefit. So I would defer to others on this. While supporting the data offset = would be convenient and match well with my specific use case I can live = without it and I don't think the size cost is significant enough to = matter. I expect to get some feedback from other developers in the = coming months regarding my Linux 3.4 integration but I doubt it would = change my current opinion on the matter. Thanks, -- Wesley Miaw= --Apple-Mail=_650297C4-27F9-4367-8D4A-7D72172190C4 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="signature.asc" Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.18 (Darwin) iQEcBAEBAgAGBQJQJF1BAAoJELoPFVk1ivvRjV8H/RbcAVBfhwD7m97iU9z6o9pB eVDxpa7RMBq/xSQGt4wfXPCBMBDmhk435bbwBAb59Y8JxVGIO28dng5aNK5OtZI0 ruLK2muNsNvum9M19RtBQyRdoXnKCndsVqe0lQeOM91Ohir+zD0UQ+PKdB0e/fY8 gxIxQeMhTSPUC0aHS/9NNEu0e0NwXCgkA69dftIIMlGdECzLJbs2hFoLdLz8Tsne Cw3iWhXe2zDEozyPxXUZTA7goqQoo6+IkKuLwmgNpUeYRPThsW+w2mcpAwwyJ/VK /EnaMSYfO7nGzgdJ72Dm1t9lAtJHmST9xADzbhsrTafQPxI4mbrx1rw3cgkMBjM= =9yB3 -----END PGP SIGNATURE----- --Apple-Mail=_650297C4-27F9-4367-8D4A-7D72172190C4-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/