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Date: Mon, 22 Dec 2025 23:12:18 +0100
From: Christoph Hellwig <hch@lst.de>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-fscrypt@vger.kernel.org
Subject: Re: [PATCH 5/9] blk-crypto: optimize bio splitting in
 blk_crypto_fallback_encrypt_bio
Message-ID: <20251222221218.GA17420@lst.de>
References: <20251217060740.923397-1-hch@lst.de> <20251217060740.923397-6-hch@lst.de> <20251219200837.GF1602@sol>
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On Fri, Dec 19, 2025 at 12:08:37PM -0800, Eric Biggers wrote:
> Actually I think using bi_max_vecs is broken.
> 
> This code assumes that bi_max_vecs matches the nr_segs that was passed
> to bio_alloc_bioset().
> 
> That assumption is incorrect, though.  If nr_segs > 0 && nr_segs <
> BIO_INLINE_VECS, bio_alloc_bioset() sets bi_max_vecs to BIO_INLINE_VECS.
> BIO_INLINE_VECS is 4.
> 
> I think blk_crypto_alloc_enc_bio() will need to return a nr_enc_pages
> value.  That value will need to be used above as well as at
> out_free_enc_bio, instead of bi_max_vecs.

A bigger bi_max_vecs should not a problem as we still have a terminating
condition based on the source bio iterator.  That being said I agree
it is not very nice, and I've reworked the code to keep a variable
counting the segments in the encrypted bio.