linux-kernel - Re: [PATCH] partitions/efi: treat size mismatch as a warning, not an error

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Message-ID: <1381451492.2367.63.camel@buesod1.americas.hpqcorp.net>
Date:	Thu, 10 Oct 2013 17:31:32 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, Karel Zak <kzak@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Sean Paul <seanpaul@...omium.org>,
	Olof Johansson <olof@...om.net>,
	Bill Richardson <wfrichar@...omium.org>,
	Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH] partitions/efi: treat size mismatch as a warning, not
 an error

On Thu, 2013-10-10 at 16:28 -0700, Doug Anderson wrote:
> In (27a7c64 partitions/efi: account for pmbr size in lba) we started
> treating bad sizes in lba field of the partition that has the 0xEE
> (GPT protective) as errors.  However, we may run into these "bad
> sizes" in the real world if someone uses dd to copy an image from a
> smaller disk to a bigger disk.  Since this case used to work (even
> without using force_gpt), keep it working and treat the size mismatch
> as a warning instead of an error.
> 
> Reported-by: Josh Triplett <josh@...htriplett.org>
> Reported-by: Sean Paul <seanpaul@...omium.org>
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>  block/partitions/efi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/block/partitions/efi.c b/block/partitions/efi.c
> index 1eb09ee..ac23dc1 100644
> --- a/block/partitions/efi.c
> +++ b/block/partitions/efi.c
> @@ -222,11 +222,15 @@ check_hybrid:
>  	 * the disk size.
>  	 *
>  	 * Hybrid MBRs do not necessarily comply with this.
> +	 *
> +	 * Consider a bad value here to be a warning to support dd-ing

dd'ing instead?

> +	 * an image from a smaller disk to a bigger disk.

'larger' disk sounds better.

>  	 */
>  	if (ret == GPT_MBR_PROTECTIVE) {
>  		sz = le32_to_cpu(mbr->partition_record[part].size_in_lba);
>  		if (sz != (uint32_t) total_sectors - 1 && sz != 0xFFFFFFFF)
> -			ret = 0;
> +			pr_warn("%s: mbr size mismatch (%u != %u)\n", __func__,
> +				sz, (uint32_t)((uint32_t) total_sectors - 1));

How about this instead?
pr_debug("GPT: mbr size in lba (%d) different than whole disk (%d).\n", sz, min(total_sectors -1, 0xFFFFFFFF));

>  	}
>  done:
>  	return ret;

Thanks,
Davidlohr

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