[dm-devel] dm-verity: Verification fails but do not see Input/Output Error on read

[Chaitra Bhat]

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Hi Mikulas,

I get 'Invalid argument' with 'iflag=direct' option when I try to read from a verity device using dd. Before I read from the device, I also did 'echo 3 > /proc/sys/vm/drop_caches' to make sure caches are dropped.

But as I said before, some locations always fail with I/O error when read and others don't.

Regards,
Chaitra
________________________________________
From: dm-devel-bounces at redhat.com [dm-devel-bounces at redhat.com] on behalf of Mikulas Patocka [mpatocka at redhat.com]
Sent: 08 August 2013 13:52
To: device-mapper development
Cc: Alasdair G Kergon
Subject: Re: [dm-devel] dm-verity: Verification fails but do not see Input/Output Error on read

On Thu, 8 Aug 2013, Chaitra Bhat wrote:

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> Hi Alasdair,
>
> Thanks for your response.
>
> But I am not convinced. Here is why...
>
> 1. I tried a bit-more and I was able to get Input/Output Error on
> certain locations - everytime - I read that location. (But I still have
> an open question that on some locations, though the verify reports
> failure, I do not get an IO Error on read)
>
> 2. I do not understand when you say device is live - do you mean
> mounted? Because I thought that the whole idea of dm-verity was that
> once the verity device is set-up, it would return EIO when something
> gets corrupted in the data or hash partitions when that invalid data is
> read.
>
> Chaitra

It is possible that you are reading data from the buffer cache and not
from the underlying device.

To not use the buffer cache, use iflag=direct parameter to dd.

Mikulas

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