linux-ext4 - Re: [PATCH] Fix EXT4_FEATURE_RO_COMPAT_HUGE

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Message-Id: <426FFD16-98B3-4427-BDA5-C80CE184781C@dilger.ca>
Date:	Mon, 23 Aug 2010 22:34:14 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Justin Maggard <jmaggard10@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] Fix EXT4_FEATURE_RO_COMPAT_HUGE_FILE check

On 2010-08-23, at 19:34, Justin Maggard wrote:
> Creating a 4TB file on a filesystem with the 64bit flag set results in e2fsck consistently complaining about i_blocks being wrong, with confusing messages like this:
> 
> That appears to be caused by ext2fs_inode_i_blocks() checking for the EXT4_FEATURE_RO_COMPAT_HUGE_FILE in the wrong place.  Fix it.
> 
> -		((fs->super->s_feature_incompat &
> +		((fs->super->s_feature_ro_compat &
> 		  EXT4_FEATURE_RO_COMPAT_HUGE_FILE) ?

This isn't the first time that we've had problems like this, and it won't be the last time unless there is a better API for checking these flags.

I've long thought about having something like:

#define EXT4_CHECK_COMPAT(sb, flag)    ((super)->s_feature_compat &     \
                                          EXT4_FEATURE_COMPAT_ ## flag)
#define EXT4_CHECK_RO_COMPAT(sb, flag) ((super)->s_feature_ro_compat &     \
                                          EXT4_FEATURE_RO_COMPAT_ ## flag)
#define EXT4_CHECK_INCOMPAT(sb, flag)  ((super)->s_feature_incompat &     \
                                          EXT4_FEATURE_INCOMPAT_ ## flag)
#define EXT4_SET_COMPAT(sb, flag)    do { (super)->s_feature_compat |=     \
                                         EXT4_FEATURE_COMPAT_ ## flag; } while(0)
#define EXT4_SET_RO_COMPAT(sb, flag) do { (super)->s_feature_ro_compat |=     \
                                         EXT4_FEATURE_RO_COMPAT_ ##flag;} while(0)
#define EXT4_SET_INCOMPAT(sb, flag)  do { (super)->s_feature_incompat |=     \
                                         EXT4_FEATURE_INCOMPAT_ ## flag;} while(0)

This will produce a compile error if the flag name and the macro name don't match. Unfortunately, for e2fsprogs we will need 3 sets of such macros because the feature flags are named EXT2_*, EXT3_*, and EXT4_*, depending on when they were added.  For the kernel code that wouldn't be needed.

Cheers, Andreas





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