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Date: Thu, 27 Jun 2024 08:14:01 +0200
From: Christoph Hellwig <hch@lst.de>
To: Anuj Gupta <anuj20.g@samsung.com>
Cc: asml.silence@gmail.com, mpatocka@redhat.com, axboe@kernel.dk,
	hch@lst.de, kbusch@kernel.org, martin.petersen@oracle.com,
	io-uring@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, Kanchan Joshi <joshi.k@samsung.com>
Subject: Re: [PATCH v2 03/10] block: copy bip_max_vcnt vecs instead of
 bip_vcnt during clone
Message-ID: <20240627061401.GA16047@lst.de>
References: <20240626100700.3629-1-anuj20.g@samsung.com> <CGME20240626101516epcas5p19fb40e8231d1832cab3d031672f0109e@epcas5p1.samsung.com> <20240626100700.3629-4-anuj20.g@samsung.com>
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In-Reply-To: <20240626100700.3629-4-anuj20.g@samsung.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

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.