linux-kernel - Re: [PATCH 3/6] fs: Convert block_read_full

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Date:   Thu, 22 Oct 2020 16:35:03 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-fscrypt@...r.kernel.org
Subject: Re: [PATCH 3/6] fs: Convert block_read_full_page to be synchronous

On Thu, Oct 22, 2020 at 10:22:25PM +0100, Matthew Wilcox (Oracle) wrote:
> Use the new blk_completion infrastructure to wait for multiple I/Os.
> Also coalesce adjacent buffer heads into a single BIO instead of
> submitting one BIO per buffer head.  This doesn't work for fscrypt yet,
> so keep the old code around for now.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/buffer.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 90 insertions(+)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 1b0ba1d59966..ccb90081117c 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2249,6 +2249,87 @@ int block_is_partially_uptodate(struct page *page, unsigned long from,
>  }
>  EXPORT_SYMBOL(block_is_partially_uptodate);
>  
> +static void readpage_end_bio(struct bio *bio)
> +{
> +	struct bio_vec *bvec;
> +	struct page *page;
> +	struct buffer_head *bh;
> +	int i, nr = 0;
> +
> +	bio_for_each_bvec_all(bvec, bio, i) {

Shouldn't this technically be bio_for_each_segment_all()?  This wants to iterate
over the pages, not the bvecs -- and in general, each bvec might contain
multiple pages.

Now, in this case, each bio has only 1 page and 1 bvec, so it doesn't really
matter.  But if we're going to use an iterator, it seems we should use the right
kind.

Likewise in decrypt_bio() in patch 6.

- Eric