On Thu, Feb 04, 2021 at 10:13:54PM -0800, Eric Biggers wrote: > On Thu, Feb 04, 2021 at 03:21:36PM -0800, Boris Burkov wrote: > > This patchset provides support for fsverity in btrfs. > > Very interested to see this! It generally looks good, but I have some > comments. > > Also, when you send this out next, can you include > linux-fscr...@vger.kernel.org, as per 'get_maintainer.pl fs/verity/'? >
Sorry for missing that, definitely will do for v2. > > At a high level, we store the verity descriptor and Merkle tree data > > in the file system btree with the file's inode as the objectid, and > > direct reads/writes to those items to implement the generic fsverity > > interface required by fs/verity/. > > > > The first patch is a preparatory patch which adds a notion of > > compat_flags to the btrfs_inode and inode_item in order to allow > > enabling verity on a file without making the file system unmountable for > > older kernels. (It runs afoul of the leaf corruption check otherwise) > > In ext4, verity is a ro_compat filesystem feature rather than a compat > feature. > That's because we wanted to prevent old kernels from writing to verity files, > which would corrupt them (get them out of sync with their Merkle trees). > > Are you sure you want to make this a "compat" flag? > I wasn't sure, so I'm glad you brought it up. That's a pretty compelling argument for making it ro_comnpat, in my opinion. I was also worried about the old kernel deleting the file and leaking the Merkle items. On the other hand, it feels a shame to make the whole file system read only over "just one file". Do you have any good strategies for getting back a file system after creating some verity files but then running a kernel without verity? I could write some utilities to list/delete verity files before doing that transition? > > > > The second patch is the bulk of the fsverity implementation. It > > implements the fsverity interface and adds verity checks for the typical > > file reading case. > > > > The third patch cleans up the corner cases in readpage, covering inline > > extents, preallocated extents, and holes. > > > > The fourth patch handles direct io of a veritied file by falling back to > > buffered io. > > > > The fifth patch adds a feature file in sysfs for verity. > > I'm also wondering if you've tested using this in combination with btrfs > compression. f2fs also supports compression and verity in combination, and > there have been some problems caused by that combination not being properly > tested. It should just work though. > I hadn't tested it with compression yet, but I'll definitely do so, especially since it was a pain point before. Thanks for the tip. > - Eric
