Re: [dm-devel] [PATCH 5.20 1/4] block: add bio_rewind() API

[Ming Lei <ming.lei@redhat.com>]

On Sun, Jun 26, 2022 at 02:37:22PM -0700, Eric Biggers wrote:
> On Fri, Jun 24, 2022 at 10:12:52PM +0800, Ming Lei wrote:
> > diff --git a/block/blk-crypto.c b/block/blk-crypto.c
> > index a496aaef85ba..caae2f429fc7 100644
> > --- a/block/blk-crypto.c
> > +++ b/block/blk-crypto.c
> > @@ -134,6 +134,21 @@ void bio_crypt_dun_increment(u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
> >  	}
> >  }
> >  
> > +/* Decrements @dun by @dec, treating @dun as a multi-limb integer. */
> > +void bio_crypt_dun_decrement(u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
> > +			     unsigned int dec)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; dec && i < BLK_CRYPTO_DUN_ARRAY_SIZE; i++) {
> > +		dun[i] -= dec;
> > +		if (dun[i] > inc)
> > +			dec = 1;
> > +		else
> > +			dec = 0;
> > +	}
> > +}
> 
> This doesn't compile.  Also this doesn't handle underflow into the next limb
> correctly.  A correct version would be:
> 
> 		u64 prev = dun[i];
> 
> 		dun[i] -= dec;
> 		if (dun[i] > prev)
> 			dec = 1;
> 		else
> 			dec = 0;

You are right, thanks for the review!

Thanks,
Ming
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