linux-ext4 - Re: [PATCH 15/41] whiteout: ext2 whiteout support

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Date:	Wed, 21 Oct 2009 15:17:38 -0600
From:	Andreas Dilger <adilger@....com>
To:	Valerie Aurora <vaurora@...hat.com>
Cc:	Jan Blunck <jblunck@...e.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Andy Whitcroft <apw@...onical.com>,
	Scott James Remnant <scott@...onical.com>,
	Sandu Popa Marius <sandupopamarius@...il.com>,
	Jan Rekorajski <baggins@...h.mimuw.edu.pl>,
	"J. R. Okajima" <hooanon05@...oo.co.jp>,
	Arnd Bergmann <arnd@...db.de>,
	Vladimir Dronnikov <dronnikov@...il.com>,
	Felix Fietkau <nbd@...nwrt.org>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Theodore Tso <tytso@....edu>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 15/41] whiteout: ext2 whiteout support

On 2009-10-21, at 13:19, Valerie Aurora wrote:
> This patch adds whiteout support to EXT2. A whiteout is an empty  
> directory
> entry (inode == 0) with the file type set to EXT2_FT_WHT. Therefore it
> allocates space in directories. Due to being implemented as a  
> filetype it is
> necessary to have the EXT2_FEATURE_INCOMPAT_FILETYPE flag set.
>
> diff --git a/include/linux/ext2_fs.h b/include/linux/ext2_fs.h
> index 121720d..bd10826 100644
> --- a/include/linux/ext2_fs.h
> +++ b/include/linux/ext2_fs.h
> @@ -189,6 +189,7 @@ struct ext2_group_desc
> +#define EXT2_OPAQUE_FL			0x00040000

Please check in the upstream e2fsprogs ext2_fs.h before defining new  
flag
values for ext2/3/4.  In this case, 0x40000 conflicts with  
EXT4_HUGE_FILE_FL,
which is of course bad.


> @@ -503,10 +504,12 @@ struct ext2_super_block {
> #define EXT2_FEATURE_INCOMPAT_META_BG		0x0010
> +#define EXT2_FEATURE_INCOMPAT_WHITEOUT		0x0020

This one doesn't conflict, probably due to luck, because 0x0040-0x0200  
are
already in use for other features.  I'm not sure if 0x0020 was  
reserved for
some other use, or just skipped to avoid potential conflicts.


Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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