From: Eric Biggers via Linux-f2fs-devel Subject: Re: [PATCH] f2fs: reserve bits for fs-verity Date: Mon, 2 Apr 2018 15:58:25 -0700 Message-ID: <20180402225825.GD59810@google.com> References: <20180328181509.199870-1-ebiggers@google.com> <9ccabf5b-46ef-aa46-bdb8-6fcd96792ed0@huawei.com> <20180330164136.GE44823@jaegeuk-macbookpro.roam.corp.google.com> <20180330183420.GA180083@google.com> <20180402184837.GA59810@google.com> <20180402214959.GG18129@dastard> Reply-To: Eric Biggers Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Theodore Ts'o , Michael Halcrow , linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jaegeuk Kim , linux-ext4@vger.kernel.org, Victor Hsieh To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20180402214959.GG18129@dastard> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net List-Id: linux-ext4.vger.kernel.org On Tue, Apr 03, 2018 at 07:49:59AM +1000, Dave Chinner wrote: > On Mon, Apr 02, 2018 at 11:48:37AM -0700, Eric Biggers wrote: > > [+Cc linux-ext4, linux-fsdevel] > > > > On Mon, Apr 02, 2018 at 06:07:10PM +0800, Chao Yu wrote: > > > Hi Eric and Jaegeuk, > > > > > > On 2018/3/31 2:34, Eric Biggers wrote: > > > > Hi Chao and Jaegeuk, > > > > > > > > On Fri, Mar 30, 2018 at 09:41:36AM -0700, Jaegeuk Kim wrote: > > > >> On 03/30, Chao Yu wrote: > > > >>> Hi Eric, > > > >>> > > > >>> On 2018/3/29 2:15, Eric Biggers wrote: > > > >>>> Reserve an F2FS feature flag and inode flag for fs-verity. This is an > > > >>>> in-development feature that is planned be discussed at LSF/MM 2018 [1]. > > > >>>> It will provide file-based integrity and authenticity for read-only > > > >>>> files. Most code will be in a filesystem-independent module, with > > > >>>> smaller changes needed to individual filesystems that opt-in to > > > >>>> supporting the feature. An early prototype supporting F2FS is available > > > >>>> [2]. Reserving the F2FS on-disk bits for fs-verity will prevent users > > > >>>> of the prototype from conflicting with other new F2FS features. > > > >>>> > > > >>>> Note that we're reserving the inode flag in f2fs_inode.i_advise, which > > > >>>> isn't really appropriate since it's not a hint or advice. But > > > >>>> ->i_advise is already being used to hold the 'encrypt' flag; and F2FS's > > > >>>> ->i_flags uses the generic FS_* values, so it seems ->i_flags can't be > > > >>>> used for an F2FS-specific flag without additional work to remove the > > > >>>> assumption that ->i_flags uses the generic flags namespace. > > > >>> > > > >>> At a glance, this is a VFS feature, can we search free slot, and define > > > >>> FS_VERITY_FL like other generic flags, so we can intergrate this flag into > > > >>> f2fs_inode::i_flags? > > > >> > > > >> Do we need to get/set this bit of i_flags to user? And, f2fs doesn't synchronize > > > >> it with inode block update. I think this should be set by internal f2fs > > > >> operations likewise fscrypt. > > > >> > > > > > > > > The fs-verity inode flag won't be modifiable using FS_IOC_SETFLAGS. Like > > > > > > Verity flag can also be wrapped by FS_FL_USER_MODIFIABLE like for FS_ENCRYPT_FL? > > > > > > > fscrypt, it will only be possible to set it using a dedicated ioctl (tentatively > > > > called FS_IOC_ENABLE_VERITY), and it won't be supported to clear the bit once > > > > set, short of deleting and re-creating the file. So it doesn't really matter > > > > where the bit goes in the on-disk inode, it just needs to go somewhere. I'm > > > > just hesitant to reserve a flag in the UAPI flags namespace which is really more > > > > "owned" by ext4 than by f2fs, so has more implications than just f2fs as we > > > > would effectively be reserving the flag for ext4's on-disk format too. > > > > > > IMO, because this is a VFS feature, it will be better that we can put it in more > > > generic place, also user can check this bit in generic way (via > > > FS_IOC_GETFLAGS), and then for other filesystem who wants add this feature, that > > > will be simple to place this bit. > > > > > > What I can see is, for encryption feature: > > > > > > vfs::i_flags > > > #define FS_ENCRYPT_FL 0x00000800 /* Encrypted file */ > > > > > > ext4:i_flags > > > #define EXT4_ENCRYPT_FL 0x00000800 /* encrypted file */ > > > > > > f2fs::i_advice > > > #define FADVISE_ENCRYPT_BIT 0x04 > > > > > > It's very wired that f2fs didn't use well defined FS_ENCRYPT_FL bit position, > > > result in that we leave a hole in on-disk i_flags, and if we want to show the > > > same 'encrypted' flags status in FS_IOC_GETFLAGS, we need to change more codes. > > > > > > Anyway, I just ask why not let generic status goes into i_flags, and private > > > status goes into i_advices? > > > > Ted and others, what would you say about allocating FS_VERITY_FL as one of the > > unused ext4 / "VFS" inode flags like 0x01000000, or maybe 0x00000400 if the > > compression flags aren't being used anymore? > > > > I do wish that we separated the on-disk flags namespaces from the > > FS_IOC_GETFLAGS/FS_IOC_SETFLAGS namespace though... Then adding the flag to > > Use FS_IOC_{GS}ETXATTR instead?. I'ts not tied to an on-disk format. > Yes, that API is better -- though, *setting* the fs-verity bit will likely be done through its own ioctl (tentatively called FS_IOC_ENABLE_VERITY) as it will involve more work than simply flipping the bit. So for *getting* it we maybe should just add it as a statx attribute, and not use the GETFLAGS or GETXATTR ioctls at all. But right now the real problem is that f2fs is using the FS_* namespace for its on-disk ->i_flags (other than a few in the f2fs-specific ->i_advise), which gives the impression that all new f2fs on-disk flags need to be exposed through FS_IOC_GETFLAGS/SETFLAGS, and also reserved for ext4 as well... Eric ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot