linux-kernel - Re: [PATCH v2 2/2] udf: support 2048-byte spacing of VRS descriptors on 4K media

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Date:   Thu, 11 Jul 2019 17:04:36 +0200
From:   Jan Kara <jack@...e.cz>
To:     " Steven J. Magnani " <steve.magnani@...idescorp.com>
Cc:     Jan Kara <jack@...e.com>,
        "Steven J . Magnani" <steve@...idescorp.com>,
        Pali Rohár <pali.rohar@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] udf: support 2048-byte spacing of VRS descriptors
 on 4K media

On Thu 11-07-19 08:38:52,  Steven J. Magnani  wrote:
> Some UDF creators (specifically Microsoft, but perhaps others) mishandle
> the ECMA-167 corner case that requires descriptors within a Volume
> Recognition Sequence to be placed at 4096-byte intervals on media where
> the block size is 4K. Instead, the descriptors are placed at the 2048-
> byte interval mandated for media with smaller blocks. This nonconformity
> currently prevents Linux from recognizing the filesystem as UDF.
> 
> Modify the driver to tolerate a misformatted VRS on 4K media.
> 
> Signed-off-by: Steven J. Magnani <steve@...idescorp.com>

Thanks for the patches! I've added them to my tree and somewhat simplified
the logic since we don't really care about nsr 2 vs 3 or whether we
actually saw BEA or not. Everything seems to work fine for me but I'd
appreciate if you could doublecheck - the result is pushed out to

git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git for_next

Thanks!

								Honza
> 
> --- a/fs/udf/super.c	2019-07-10 20:55:33.334359446 -0500
> +++ b/fs/udf/super.c	2019-07-10 21:20:58.138382326 -0500
> @@ -741,6 +741,7 @@ static int udf_check_vsd(struct super_bl
>  	int sectorsize;
>  	struct buffer_head *bh = NULL;
>  	int nsr = 0;
> +	int quirk_nsr = 0;
>  	struct udf_sb_info *sbi;
>  
>  	sbi = UDF_SB(sb);
> @@ -780,11 +781,27 @@ static int udf_check_vsd(struct super_bl
>  		if (vsd_id > nsr)
>  			nsr = vsd_id;
>  
> +		/* Special handling for improperly formatted VRS (e.g., Win10)
> +		 * where components are separated by 2048 bytes
> +		 * even though sectors are 4K
> +		 */
> +		if ((sb->s_blocksize == 4096) && (quirk_nsr < 2)) {
> +			vsd_id = identify_vsd(vsd + 1);
> +			if ((nsr == 1) || (quirk_nsr == 1)) {
> +				/* BEA01 has been seen, allow quirk NSR */
> +				if (vsd_id > quirk_nsr)
> +					quirk_nsr = vsd_id;
> +			} else if (vsd_id > 3)
> +				quirk_nsr = vsd_id;  /* 0 -> 255 */
> +		}
> +
>  		brelse(bh);
>  	}
>  
>  	if ((nsr >= 2) && (nsr <= 3))
>  		return nsr;
> +	else if ((quirk_nsr >= 2) && (quirk_nsr <= 3))
> +		return quirk_nsr;
>  	else if (!bh && sector - (sbi->s_session << sb->s_blocksize_bits) ==
>  			VSD_FIRST_SECTOR_OFFSET)
>  		return -1;
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR