Re: [PATCH v2 06/23] fsverity: add drop_page() callout

Andrey Albershteyn
2023-04-05T10:39:14Z

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@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().

Sure, this makes more sense, thank you!

--
- Andrey