From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from down.free-electrons.com ([37.187.137.238] helo=mail.free-electrons.com) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bFjW6-0002C7-Lz for linux-mtd@lists.infradead.org; Wed, 22 Jun 2016 14:52:35 +0000 Date: Wed, 22 Jun 2016 16:52:12 +0200 From: Boris Brezillon To: Richard Weinberger Cc: "linux-mtd@lists.infradead.org" , Artem Bityutskiy , Alexander Kaplan , Brian Norris , Ezequiel Garcia Subject: Re: [RFC] Raising the UBI version Message-ID: <20160622165212.76c17d0a@bbrezillon> In-Reply-To: <576AA425.8070705@nod.at> 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> <576AA425.8070705@nod.at> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 22 Jun 2016 16:43:49 +0200 Richard Weinberger wrote: > 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. Then you still miss the version concept. Again, versions and features are orthogonal, and you're not guaranteed that we'll never change the on-flash format in an incompatible way... So how about defining the following: - /sys/class/ubi/version: user-space ABI version (should always be one) - /sys/class/ubi/supported-on-flash-formats: either a bitfield or an integer representing the higher on-flash format version supported by the implementation (which implies that implementations have to support all on-flash formats up-to supported-on-flash-formats) - /sys/class/ubi/supported-features: the features supported by the implementation (each bit is a specific feature or a set of features). The features may or may not be version dependent. - /sys/class/ubi/ubiX/on-flash-format: the on-flash format used on the UBIX device - /sys/class/ubi/ubiX/features: the features exposed by this UBIX device