Re: [PATCH 2/3] btrfs: add helper to initialize the non-bio part of btrfs_io_bio

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Jun 12, 2017 at 05:29:39PM +0200, David Sterba wrote:
> We use btrfs_bioset for bios and ask to allocate the entire size of
> btrfs_io_bio from btrfs bio_alloc_bioset. The member 'bio' is
> initialized but the bytes from 0 to offset of 'bio' are left
> uninitialized. Although we initialize some of the members in our
> helpers, we should initialize the whole structures.
> 

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

-liubo
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/extent_io.c | 30 ++++++++++++++----------------
>  1 file changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 5037fd918f43..cbd0a9a1daa5 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2654,22 +2654,28 @@ static void end_bio_extent_readpage(struct bio *bio)
>  }
>  
>  /*
> + * Initialize the members up to but not including 'bio'. Use after allocating a
> + * new bio by bio_alloc_bioset as it does not initialize the bytes outside of
> + * 'bio' because use of __GFP_ZERO is not supported.
> + */
> +static inline void btrfs_io_bio_init(struct btrfs_io_bio *btrfs_bio)
> +{
> +	memset(btrfs_bio, 0, offsetof(struct btrfs_io_bio, bio));
> +}
> +
> +/*
>   * The following helpers allocate a bio. As it's backed by a bioset, it'll
>   * never fail.  We're returning a bio right now but you can call btrfs_io_bio
>   * for the appropriate container_of magic
>   */
>  struct bio *btrfs_bio_alloc(struct block_device *bdev, u64 first_byte)
>  {
> -	struct btrfs_io_bio *btrfs_bio;
>  	struct bio *bio;
>  
>  	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_PAGES, btrfs_bioset);
>  	bio->bi_bdev = bdev;
>  	bio->bi_iter.bi_sector = first_byte >> 9;
> -	btrfs_bio = btrfs_io_bio(bio);
> -	btrfs_bio->csum = NULL;
> -	btrfs_bio->csum_allocated = NULL;
> -	btrfs_bio->end_io = NULL;
> +	btrfs_io_bio_init(btrfs_io_bio(bio));
>  	return bio;
>  }
>  
> @@ -2681,24 +2687,18 @@ struct bio *btrfs_bio_clone(struct bio *bio)
>  	/* Bio allocation backed by a bioset does not fail */
>  	new = bio_clone_fast(bio, GFP_NOFS, btrfs_bioset);
>  	btrfs_bio = btrfs_io_bio(new);
> -	btrfs_bio->csum = NULL;
> -	btrfs_bio->csum_allocated = NULL;
> -	btrfs_bio->end_io = NULL;
> +	btrfs_io_bio_init(btrfs_bio);
>  	btrfs_bio->iter = bio->bi_iter;
>  	return new;
>  }
>  
>  struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
>  {
> -	struct btrfs_io_bio *btrfs_bio;
>  	struct bio *bio;
>  
>  	/* Bio allocation backed by a bioset does not fail */
>  	bio = bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
> -	btrfs_bio = btrfs_io_bio(bio);
> -	btrfs_bio->csum = NULL;
> -	btrfs_bio->csum_allocated = NULL;
> -	btrfs_bio->end_io = NULL;
> +	btrfs_io_bio_init(btrfs_io_bio(bio));
>  	return bio;
>  }
>  
> @@ -2712,9 +2712,7 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
>  	ASSERT(bio);
>  
>  	btrfs_bio = btrfs_io_bio(bio);
> -	btrfs_bio->csum = NULL;
> -	btrfs_bio->csum_allocated = NULL;
> -	btrfs_bio->end_io = NULL;
> +	btrfs_io_bio_init(btrfs_bio);
>  
>  	bio_trim(bio, offset >> 9, size >> 9);
>  	btrfs_bio->iter = bio->bi_iter;
> -- 
> 2.13.0
>