Re: [PATCH v5 07/25] iomap: introduce IOMAP_F_FSVERITY and teach writeback to handle fsverity

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Mar 25, 2026 at 01:38:07PM +0100, Andrey Albershteyn wrote:
> On 2026-03-25 09:00:21, Christoph Hellwig wrote:
> > > @@ -353,9 +353,16 @@ static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
> > >  {
> > >  	const struct iomap *srcmap = iomap_iter_srcmap(iter);
> > >  
> > > -	return srcmap->type != IOMAP_MAPPED ||
> > > -		(srcmap->flags & IOMAP_F_NEW) ||
> > > -		pos >= i_size_read(iter->inode);
> > > +	if (srcmap->type != IOMAP_MAPPED)
> > > +		return true;
> > > +
> > > +	if (srcmap->flags & IOMAP_F_NEW)
> > > +		return true;
> > > +
> > > +	if (srcmap->flags & IOMAP_F_FSVERITY)
> > > +		return false;
> > > +
> > > +	return pos >= i_size_read(iter->inode);
> > 
> > This might be a good time to document the various reasons for needing
> > zeroing.
> 
> something like this?
> 
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -344,9 +344,27 @@ static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
>  {
>         const struct iomap *srcmap = iomap_iter_srcmap(iter);
>  
> -       return srcmap->type != IOMAP_MAPPED ||
> -               (srcmap->flags & IOMAP_F_NEW) ||
> -               pos >= i_size_read(iter->inode);
> +       /*
> +        * If this block is not mapped, we don't have any backing blocks to read
> +        * yet

	/* If this block has not been written, there's nothing to read */

> +        */
> +       if (srcmap->type != IOMAP_MAPPED)
> +               return true;
> +
> +       /*
> +        * This block just got allocated and does not contain any meaningful data
> +        */

	/* Newly allocated blocks have not been written */

Otherwise looks good to me.

--D

> +       if (srcmap->flags & IOMAP_F_NEW)
> +               return true;
> +
> +       /*
> +        * fsverity metadata is stored past i_size, we need to read it instead of
> +        * zeroing
> +        */
> +       if (srcmap->flags & IOMAP_F_FSVERITY)
> +               return false;
> +
> +       return pos >= i_size_read(iter->inode);
>  }
> 
> > 
> > > +/*
> > > + * IO happens beyond inode EOF, fsverity metadata is stored there
> > > + */
> > > +#define IOMAP_F_FSVERITY	(1U << 10)
> > 
> > This comment feels a bit too sparse.  Here is my interpretation of what
> > this flag does:
> > 
> > /*
> >  * Indicates reads and writes of fsverity metadata.
> >  *
> >  * Fsverity metadata is stored after the regular file data and thus beyond
> >  * i_size.
> >  */
> 
> Thanks! I will update it
> 
> -- 
> - Andrey
> 
>