Re: [PATCH 30/32] union mount: ext2 fallthru support

From: Andreas Dilger <adilger@sun.com>
To: Jan Blunck <jblunck@suse.de>
Cc: viro@zeniv.linux.org.uk, bharata@in.ibm.com, dwmw2@infradead.org,
	mszeredi@suse.cz, vaurora@redhat.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 30/32] union mount: ext2 fallthru support
Date: Mon, 18 May 2009 10:32:21 -0600	[thread overview]
Message-ID: <20090518163221.GE3144@webber.adilger.int> (raw)
In-Reply-To: <1242662968-11684-31-git-send-email-jblunck@suse.de>

On May 18, 2009  18:09 +0200, Jan Blunck wrote:
> diff --git a/include/linux/ext2_fs.h b/include/linux/ext2_fs.h
> index bd10826..f6b68ec 100644
> --- a/include/linux/ext2_fs.h
> +++ b/include/linux/ext2_fs.h
> @@ -577,6 +577,7 @@ enum {
>  	EXT2_FT_SOCK,
>  	EXT2_FT_SYMLINK,
>  	EXT2_FT_WHT,
> +	EXT2_FT_FALLTHRU,
>  	EXT2_FT_MAX

The EXT2_FT_WHT is not declared in e2fsprogs::lib/ext2fs/ext2_fs.h
so you risk hitting a conflict here if someone isn't looking at
the "should be left alone" ext2 code.  Secondly, it is somewhat
dangerous to use a straight enum here, because this will reassign
values of later variables if one of the earlier ones is removed.

For enums like this that require specific constant on-disk values
I prefer being safe:

enum {
	EXT2_FT_UNKNOWN  = 0,
	EXT2_FT_REG_FILE = 1,
	EXT2_FT_DIR	 = 2,
	EXT2_FT_CHRDEV   = 3,
	EXT2_FT_BLKDEV   = 4,
	EXT2_FT_FIFO     = 5,
	EXT2_FT_SOCK     = 6,
	EXT2_FT_SYMLINK  = 7,
	EXT2_FT_WHT      = 8,
	EXT2_FT_FALLTHRU = 9,
 	EXT2_FT_MAX

It probably also makes sense to include a patch for ext3/ext4 to ensure
these values are not used by some unrelated feature.

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