Re: [PATCH v6 2/3] btrfs: initial fsverity support

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Sep 14, 2021 at 11:34:29AM -0700, Boris Burkov wrote:
> > Okay, so it is used.  (Due to the macro, it didn't show up when grepping.)
> > 
> > Doesn't it defeat the purpose of a ro_compat inode flag if the whole filesystem
> > is marked with a ro_compat feature flag, though?  I thought that the point of
> > the ro_compat inode flag is to allow old kernels to mount the filesystem
> > read-write, with only verity files being forced to read-only.  That would be
> > more flexible than ext4's implementation of fs-verity which forces the whole
> > filesystem to read-only.  But it seems you're forcing the whole filesystem to
> > read-only anyway?
> > 
> > - Eric
> 
> I was thinking of it in terms of "RO compat is the goal" and having new
> inode flags totally broke that and was treated as a corruption of the
> inode regardless of the fs being ro/rw. I think a check on a live fs
> would just flip the fs ro, which was the goal anyway, but a check that
> happened during mount would fail the mount, even for a read-only fs. 
> 
> Making it fully per file would be pretty cool! The only thing
> really missing as far as I can tell is a way to mark a file read only
> with the same semantics fsverity uses from within btrfs.

I don't understand.  Why are you bothering with the ro_compat inode flag at all
if it doesn't actually work?

- Eric