[PATCH v2 03/10] block: copy bip_max_vcnt vecs instead of bip_vcnt during clone

[Christoph Hellwig]

On Wed, Jun 26, 2024 at 03:36:53PM +0530, Anuj Gupta wrote:
> If bio_integrity_copy_user is used to process the meta buffer, bip_max_vcnt
> is one greater than bip_vcnt.

Why?

> @@ -647,12 +647,12 @@ int bio_integrity_clone(struct bio *bio, struct bio *bio_src,
>  
>  	BUG_ON(bip_src == NULL);
>  
> -	bip = bio_integrity_alloc(bio, gfp_mask, bip_src->bip_vcnt);
> +	bip = bio_integrity_alloc(bio, gfp_mask, bip_src->bip_max_vcnt);
>  	if (IS_ERR(bip))
>  		return PTR_ERR(bip);
>  
>  	memcpy(bip->bip_vec, bip_src->bip_vec,
> -	       bip_src->bip_vcnt * sizeof(struct bio_vec));
> +	       bip_src->bip_max_vcnt * sizeof(struct bio_vec));
>  
>  	bip->bip_vcnt = bip_src->bip_vcnt;
>  	bip->bip_iter = bip_src->bip_iter;

So trying to compare this to how the bio data path is cloned, it seems
like bio_integrity_clone is still copying the bvec array.  With the
concept of the immutable bvecs we've had for years this should not
be required.  That is reuse the actual bio_vecs, and just copy
the iter similar to bio_alloc_clone/__bio_clone.