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Date:   Wed, 5 Apr 2023 09:40:19 +1000
From:   Dave Chinner <david@fromorbit.com>
To:     Andrey Albershteyn <aalbersh@redhat.com>
Cc:     djwong@kernel.org, dchinner@redhat.com, ebiggers@kernel.org,
        hch@infradead.org, linux-xfs@vger.kernel.org,
        fsverity@lists.linux.dev, rpeterso@redhat.com, agruenba@redhat.com,
        xiang@kernel.org, chao@kernel.org,
        damien.lemoal@opensource.wdc.com, jth@kernel.org,
        linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
        cluster-devel@redhat.com
Subject: Re: [PATCH v2 06/23] fsverity: add drop_page() callout
Message-ID: <20230404234019.GM3223426@dread.disaster.area>
References: <20230404145319.2057051-1-aalbersh@redhat.com>
 <20230404145319.2057051-7-aalbersh@redhat.com>
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On Tue, Apr 04, 2023 at 04:53:02PM +0200, Andrey Albershteyn wrote:
> Allow filesystem to make additional processing on verified pages
> instead of just dropping a reference. This will be used by XFS for
> internal buffer cache manipulation in further patches. The btrfs,
> ext4, and f2fs just drop the reference.
> 
> Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
> ---
>  fs/btrfs/verity.c         | 12 ++++++++++++
>  fs/ext4/verity.c          |  6 ++++++
>  fs/f2fs/verity.c          |  6 ++++++
>  fs/verity/read_metadata.c |  4 ++--
>  fs/verity/verify.c        |  6 +++---
>  include/linux/fsverity.h  | 10 ++++++++++
>  6 files changed, 39 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
> index c5ff16f9e9fa..4c2c09204bb4 100644
> --- a/fs/btrfs/verity.c
> +++ b/fs/btrfs/verity.c
> @@ -804,10 +804,22 @@ static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
>  			       pos, buf, size);
>  }
>  
> +/*
> + * fsverity op that releases the reference obtained by ->read_merkle_tree_page()
> + *
> + * @page:  reference to the page which can be released
> + *
> + */
> +static void btrfs_drop_page(struct page *page)
> +{
> +	put_page(page);
> +}
> +
>  const struct fsverity_operations btrfs_verityops = {
>  	.begin_enable_verity     = btrfs_begin_enable_verity,
>  	.end_enable_verity       = btrfs_end_enable_verity,
>  	.get_verity_descriptor   = btrfs_get_verity_descriptor,
>  	.read_merkle_tree_page   = btrfs_read_merkle_tree_page,
>  	.write_merkle_tree_block = btrfs_write_merkle_tree_block,
> +	.drop_page		 = &btrfs_drop_page,
>  };

Ok, that's a generic put_page() call.

....
> diff --git a/fs/verity/verify.c b/fs/verity/verify.c
> index f50e3b5b52c9..c2fc4c86af34 100644
> --- a/fs/verity/verify.c
> +++ b/fs/verity/verify.c
> @@ -210,7 +210,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
>  		if (is_hash_block_verified(vi, hpage, hblock_idx)) {
>  			memcpy_from_page(_want_hash, hpage, hoffset, hsize);
>  			want_hash = _want_hash;
> -			put_page(hpage);
> +			inode->i_sb->s_vop->drop_page(hpage);
>  			goto descend;

			fsverity_drop_page(hpage);

static inline void
fsverity_drop_page(struct inode *inode, struct page *page)
{
	if (inode->i_sb->s_vop->drop_page)
		inode->i_sb->s_vop->drop_page(page);
	else
		put_page(page);
}

And then you don't need to add the functions to each of the
filesystems nor make an indirect call just to run put_page().

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com