From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from b.ns.miles-group.at ([95.130.255.144] helo=radon.swed.at) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bFjO1-0006M4-RK for linux-mtd@lists.infradead.org; Wed, 22 Jun 2016 14:44:14 +0000 Subject: Re: [RFC] Raising the UBI version To: Boris Brezillon References: <57699356.4030802@nod.at> <20160622144344.07ba4d41@bbrezillon> <576A989A.6080502@nod.at> <20160622160118.28a4339a@bbrezillon> <576A9B1D.3010201@nod.at> <20160622161304.6a16da85@bbrezillon> <576A9EF0.9020007@nod.at> <20160622163947.36ac7f3e@bbrezillon> Cc: "linux-mtd@lists.infradead.org" , Artem Bityutskiy , Alexander Kaplan , Brian Norris , Ezequiel Garcia From: Richard Weinberger Message-ID: <576AA425.8070705@nod.at> Date: Wed, 22 Jun 2016 16:43:49 +0200 MIME-Version: 1.0 In-Reply-To: <20160622163947.36ac7f3e@bbrezillon> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Am 22.06.2016 um 16:39 schrieb Boris Brezillon: > On Wed, 22 Jun 2016 16:21:36 +0200 > Richard Weinberger wrote: > >> Am 22.06.2016 um 16:13 schrieb Boris Brezillon: >>>> /sys/class/ubi/version is the version of the UBI implementation, >>>> not the version of the attached UBI image. >>>> It will the here as soon you load the UBI module. >>> >>> Do we have /sys/class/ubi/ubiX/version for the UBI image version? >> >> No. That's why I plan to add /sys/class/ubi/ubiX/features_used to >> show which features the attached UBI image requested. >> And having a /sys/class/ubi/ubi/features which denotes what features >> the _implementation_ supports. > > Still the version and features are encoding different things IMO. > Incrementing the on-flash version means that the on-flash format has > changed in an incompatible way, while features denotes the fact that > the existing format has been extended with new features but is backward > compatible. Yes. But now we have a mix of both. ;-\ >> >>> This is still unclear to me why we need to version the >>> user-space/kernel-space ABI, since it's supposed to be backward >>> compatible, so adding new features requires adding new ioctls and >>> keeping the old ones in a working state. >>> >>> What is /sys/class/ubi/version actually encoding? Isn't it encoding the >>> fact that a specific UBI implementation is supporting all UBI on-flash >>> formats up to format version X (that was my understanding)? >>> >> >> Well, /sys/class/ubi/version exports UBI_VERSION from ubi-media.h. >> It is (ab)used to encode the ABI version *and* the on-flash version. > > The on-flash versions supported by the implementation is a useful > information. > >> The problem is that mtd-utils libubi will refuse to work with >> /sys/class/ubi/version unequal 1. >> >> Here the gem from libubi: >> if (read_positive_int(lib->ubi_version, &version)) >> goto out_error; >> if (version != LIBUBI_UBI_VERSION) { >> errmsg("this library was made for UBI version %d, but UBI " >> "version %d is detected\n", LIBUBI_UBI_VERSION, version); >> goto out_error; >> } > > And this is where the problem is: libubi does not make proper use of > this information. We should either have > > if (version >= LIBUBI_UBI_VERSION) > > or, if we decide that version is a bitfield directly encoding which > versions are supported by the implementation > > #define VERSION_SUPPORTED(version, x) ((version) & BIT((x)-1))) > > if (VERSION_SUPPORTED(version, 1)) Yep. But we cannot change already compiled and shipped code. >> >> This is why I want to hardcode it to 1. >> Everything else will break existing user space in some way. >> 10 years ago /sys/class/ubi/version seemed like a good idea >> but now it hits us hard. > > Yes, I understand that, but this also means /sys/class/ubi/version is > just a dummy file which only purpose is to make libubi happy :). That's the plan. > If this is the case, then I think we should have another file encoding > the supported on-flash formats... This is what /sys/class/ubi/features was supposed to do. Thanks, //richard