Re: [PATCH 05/12] iomap: Introduce IOMAP_ENCODED

[Christoph Hellwig <hch@infradead.org>]

On Fri, Oct 04, 2024 at 04:04:32PM -0400, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> An encoded extent must be read completely. Make the bio just as a
> regular bio and let filesystem deal with the rest of the extent.
> A new bio must be created if a new iomap is returned.
> The filesystem must be informed that the bio to be read is
> encoded and the offset from which the encoded extent starts. So, pass
> the iomap associated with the bio while calling submit_io. Save the
> previous iomap (associated with the bio being submitted) in prev in
> order to submit when the iomap changes.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>  fs/iomap/buffered-io.c | 17 ++++++++++-------
>  include/linux/iomap.h  | 11 +++++++++--
>  2 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 0e682ff84e4a..4c734899a8e5 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -378,12 +378,13 @@ 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 ||
> +	return (srcmap->type != IOMAP_MAPPED &&
> +			srcmap->type != IOMAP_ENCODED) ||
>  		(srcmap->flags & IOMAP_F_NEW) ||
>  		pos >= i_size_read(iter->inode);

Non-standard indentation for the new line.  But at this point the
condition is becoming complex enough that it is best split into
multiple if statements anyway.


>  	sector = iomap_sector(iomap, pos);
>  	if (!ctx->bio ||
> +	    (iomap->type & IOMAP_ENCODED && iomap->offset != iter->prev.offset) ||

Overly long line.  And this could really use a comment as well.

> -static loff_t iomap_readahead_iter(const struct iomap_iter *iter,
> +static loff_t iomap_readahead_iter(struct iomap_iter *iter,
>  		struct iomap_readpage_ctx *ctx)

Why is the iter de-constified?

In general I'm not a huge fan of the encoded magic here, but I'll
need to take a closer look at the caller if I can come up with
something better.