Re: [PATCH v2 2/3] dm-inlinecrypt: add target for inline block device encryption

[Benjamin Marzinski]

On Mon, Apr 27, 2026 at 01:23:27AM -0400, Benjamin Marzinski wrote:
> On Fri, Apr 10, 2026 at 06:40:30AM -0700, Linlin Zhang wrote:
> > From: Eric Biggers <ebiggers@xxxxxxxxxx>
> > +	/*
> > +	 * Since we've added an encryption context to the bio and
> > +	 * blk-crypto-fallback may be needed to process it, it's necessary to
> > +	 * use the fallback-aware bio submission code rather than
> > +	 * unconditionally returning DM_MAPIO_REMAPPED.
> > +	 *
> > +	 * To get the correct accounting for a dm target in the case where
> > +	 * __blk_crypto_submit_bio() doesn't take ownership of the bio (returns
> > +	 * true), call __blk_crypto_submit_bio() directly and return
> > +	 * DM_MAPIO_REMAPPED in that case, rather than relying on
> > +	 * blk_crypto_submit_bio() which calls submit_bio() in that case.
> > +	 */
> > +	if (__blk_crypto_submit_bio(bio))
> 
> This will still double account for fallback writes (which call
> submit_bio() on the encrypted bios, and return DM_MAPIO_SUBMITTED here). 

Just to clarify, I'm talking about the vmstats accounting. The IO
originally gets accounted by submit_bio() when the bio is submitted to
the dm device. For actual inline encryption and fallback reads, dm will
submit the bio to the underlying device using submit_bio_noacct() to
avoid double-counting the IO.

For fallback writes, __blk_crypto_submit_bio() will submit the encrypted
bios to the underlying device with submit_bio(). This adds the IO
sectors again, even though it's the same IO, only encrypted now.

-Ben

> 
> -Ben
> 
> > +		return DM_MAPIO_REMAPPED;
> > +	return DM_MAPIO_SUBMITTED;
> > +}
>