Re: [PATCH v4] btrfs: send: add support for fs-verity

[David Sterba <dsterba@suse.cz>]

On Mon, Aug 15, 2022 at 01:54:28PM -0700, Boris Burkov wrote:
> Preserve the fs-verity status of a btrfs file across send/recv.
> 
> There is no facility for installing the Merkle tree contents directly on
> the receiving filesystem, so we package up the parameters used to enable
> verity found in the verity descriptor. This gives the receive side
> enough information to properly enable verity again. Note that this means
> that receive will have to re-compute the whole Merkle tree, similar to
> how compression worked before encoded_write.
> 
> Since the file becomes read-only after verity is enabled, it is
> important that verity is added to the send stream after any file writes.
> Therefore, when we process a verity item, merely note that it happened,
> then actually create the command in the send stream during
> 'finish_inode_if_needed'.
> 
> This also creates V3 of the send stream format, without any format
> changes besides adding the new commands and attributes.
> 
> Signed-off-by: Boris Burkov <boris@bur.io>

As for the merge target, a realistic one seems to be 6.2, we have too
many pending patches everywhere else. There's a todo list for v3 that
I'd really like to get done.

To be able to test things incrementally until then we can add v3 support
under debug config.

> --
> Changes in v4:
> - Use btrfs_get_verity_descriptor instead of verity ops get descriptor.
>   Move that definition to ctree.h for conditional building. This cleaned
>   up most of the conditional building issues, in my opinion.

Yes, that way it's ok.

> - Rename process_new_verity to process_verity.
> - Use le-to-cpu conversion for all fsverity descriptor fields.
> - Don't check NULL for kvfree of the send descriptor.

> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -3,6 +3,7 @@
>   * Copyright (C) 2012 Alexander Block.  All rights reserved.
>   */
>  
> +#include "linux/compiler_attributes.h"

As Eric pointed out, this is not necessary, I'll delete the line, no
need to resend just for that.