From mboxrd@z Thu Jan 1 00:00:00 1970 From: Heinz Mauelshagen Subject: Re: [PATCH 1/1] dm raid: fix compat_features validation Date: Fri, 14 Oct 2016 19:14:32 +0200 Message-ID: References: <20161011142835.11620-1-apw@canonical.com> <1c517f14-1234-7844-fc6a-cd1b9698fb8b@redhat.com> <20161011153808.nmyf6hafjaadcemw@brain> <591b9d8d-2036-2d0f-14f2-af176b5beaea@redhat.com> <20161011174421.GA25738@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20161011174421.GA25738@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: Andy Whitcroft , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, dm-devel@redhat.com, Shaohua Li , Alasdair Kergon List-Id: linux-raid.ids On 10/11/2016 07:44 PM, Mike Snitzer wrote: > On Tue, Oct 11 2016 at 11:44am -0400, > Heinz Mauelshagen wrote: > >> >> On 10/11/2016 05:38 PM, Andy Whitcroft wrote: >>> On Tue, Oct 11, 2016 at 05:04:34PM +0200, Heinz Mauelshagen wrote: >>>> Andy, >>>> >>>> good catch. >>>> >>>> We should rather check for V190 support only in case any >>>> compat feature flags are actually set. >>>> >>>> { >>>> + if (le32_to_cpu(sb->compat_features) && >>>> + le32_to_cpu(sb->compat_features) != FEATURE_FLAG_SUPPORTS_V190) >>>> { >>>> rs->ti->error = "Unable to assemble array: Unknown flag(s) >>>> in compatible feature flags"; >>>> return -EINVAL; >>>> } >>> If the feature flags are single bit combinations then I believe the >>> below does check exactly that. Checking for no 1s outside of the >>> expected features, caring not for the value of the valid bits: >>> >>> + if (le32_to_cpu(sb->compat_features) & ~(FEATURE_FLAG_SUPPORTS_V190)) { >>> >>> with the possibilty to or in additional feature bits as they are added. >> Thanks, >> I prefer this to be easier readable. > Readable or not, the code with the != is _not_ future-proof. Whereas > Andy's solution is. If/when a new compat feature comes along then > FEATURE_FLAG_SUPPORTS_V190 would be replaced to be a macro that ORs all > the new compat features together (e.g. FEATURE_FLAG_COMPAT). E.g. how > dm-thin-metadata.c:__check_incompat_features() does. If we'll have to introduce more feature flags in the future (e.g. for clustered raid1 support), this is going to be based on the test_bit() API for consistency with any other flag processing we do in the target. Heinz > We can go with the != code for now, since any future changes would > likely cause this test to be changed. Or we could fix it now _for > real_. > > Mike