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Date:   Wed, 5 Apr 2023 12:39:04 +0200
From:   Andrey Albershteyn <aalbersh@...hat.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     djwong@...nel.org, dchinner@...hat.com, ebiggers@...nel.org,
        hch@...radead.org, linux-xfs@...r.kernel.org,
        fsverity@...ts.linux.dev, rpeterso@...hat.com, agruenba@...hat.com,
        xiang@...nel.org, chao@...nel.org,
        damien.lemoal@...nsource.wdc.com, jth@...nel.org,
        linux-erofs@...ts.ozlabs.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel@...hat.com
Subject: Re: [PATCH v2 06/23] fsverity: add drop_page() callout

Hi Dave,

On Wed, Apr 05, 2023 at 09:40:19AM +1000, Dave Chinner wrote:
> 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@...hat.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().

Sure, this makes more sense, thank you!

-- 
- Andrey

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