On Mon, Jan 09, 2023 at 07:05:07PM -0800, Eric Biggers wrote: > On Mon, Jan 09, 2023 at 06:37:59PM -0800, Andrew Morton wrote: > > On Fri, 23 Dec 2022 12:36:37 -0800 Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > > After each filesystem block (as represented by a buffer_head) has been > > > read from disk by block_read_full_folio(), verify it if needed. The > > > verification is done on the fsverity_read_workqueue. Also allow reads > > > of verity metadata past i_size, as required by ext4. > > > > Sigh. Do we reeeeealy need to mess with buffer.c in this fashion? Did > > any other subsystems feel a need to do this? > > ext4 is currently the only filesystem that uses block_read_full_folio() and that > supports fsverity. However, since fsverity has a common infrastructure across > filesystems, in fs/verity/, it makes sense to support it in the other filesystem > infrastructure so that things aren't mutually exclusive for no reason. > > Note that this applies to fscrypt too, which block_read_full_folio() (previously > block_read_full_page()) already supports since v5.5. > > If you'd prefer that block_read_full_folio() be copied into ext4, then modified > to support fscrypt and fsverity, and then the fscrypt support removed from the > original copy, we could do that. That seems more like a workaround to avoid > modifying certain files than an actually better solution, but it could be done. > > > > > > This is needed to support fsverity on ext4 filesystems where the > > > filesystem block size is less than the page size. > > > > Does any real person actually do this? > > Yes, on systems with the page size larger than 4K, the ext4 filesystem block > size is often smaller than the page size. ext4 encryption (fscrypt) originally > had the same limitation, and Chandan Rajendra from IBM did significant work to > solve it a few years ago, with the changes landing in v5.5. > > - Eric Any more thoughts on this from Andrew, the ext4 maintainers, or anyone else? - Eric
