linux-kernel - Re: [PATCH] dm-verity: do forward error correction on metadata I/O errors

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Message-ID: <60c1acde-839d-4d23-8270-2acf032a4ef9@gmail.com>
Date: Mon, 10 Feb 2025 17:39:32 +0100
From: Milan Broz <gmazyland@...il.com>
To: Mikulas Patocka <mpatocka@...hat.com>,
 Akilesh Kailash <akailash@...gle.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>, kernel-team@...roid.com,
 Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
 dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm-verity: do forward error correction on metadata I/O
 errors

On 2/10/25 4:04 PM, Mikulas Patocka wrote:
> Do forward error correction if metadata I/O fails.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

Not directly related to this patch, but...
please could you also increase the dm-verity version?

I just implemented support for the errors-as-corruption
dm-verity flags in veritysetup.

The version of dm-verity stayed at 1.10 for a very long, and
the IO error processing change was a functional change that we
would like to detect.
We cannot set version retrospectively, but at least now with other
changes.

(Veritysetup tries the requested flags; if activation fails,
it displays a better error message based on the detected
target version. That way it works even with backports.)

Thanks,
Milan


> 
> ---
>   drivers/md/dm-verity-target.c |   19 +++++++++++++++++--
>   1 file changed, 17 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-verity-target.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-verity-target.c	2025-02-04 13:52:45.000000000 +0100
> +++ linux-2.6/drivers/md/dm-verity-target.c	2025-02-10 15:55:42.000000000 +0100
> @@ -324,8 +324,22 @@ static int verity_verify_level(struct dm
>   						&buf, bio->bi_ioprio);
>   	}
>   
> -	if (IS_ERR(data))
> -		return PTR_ERR(data);
> +	if (IS_ERR(data)) {
> +		r = PTR_ERR(data);
> +		data = dm_bufio_new(v->bufio, hash_block, &buf);
> +		if (IS_ERR(data))
> +			return r;
> +		if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_METADATA,
> +				      hash_block, data) == 0) {
> +			aux = dm_bufio_get_aux_data(buf);
> +			aux->hash_verified = 1;
> +			goto release_ok;
> +		} else {
> +			dm_bufio_release(buf);
> +			dm_bufio_forget(v->bufio, hash_block);
> +			return r;
> +		}
> +	}
>   
>   	aux = dm_bufio_get_aux_data(buf);
>   
> @@ -366,6 +380,7 @@ static int verity_verify_level(struct dm
>   		}
>   	}
>   
> +release_ok:
>   	data += offset;
>   	memcpy(want_digest, data, v->digest_size);
>   	r = 0;
>