linux-ext4 - Re: uninit_bg compatibility?

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Message-Id: <40E7666A-17B8-4D39-A078-8FE3379C2AA5@dilger.ca>
Date:	Tue, 21 Sep 2010 10:00:22 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Bo Brantén <bosse@....umu.se>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: uninit_bg compatibility?

On 2010-09-21, at 06:28, Bo Brantén wrote:
> when writing new files to an ext4 file system using the Windows driver fsck will later complain "Group descriptor nn checksum is invalid" and I think that is because it used an yet unused block group without knowing that they can be marked as uninitialized. So I thought a simple patch would be to mount the file system read-only if that feature is in use untill the driver is updated with full write support but I can't find the flag to use, there is no EXT4_FEATURE_RO_COMPAT_UNINIT_BG so I thought I ask here if anyone could clear this out.

The Windows driver (or any driver for that matter) should ONLY allow read-only access if ANY feature in s_feature_ro_compat is unknown, and completely refuse to mount if any feature in s_feature_incompat is unknown.

The actual feature flag is called EXT4_FEATURE_RO_COMPAT_GDT_CSUM, but that doesn't matter, since what the code should be doing is masking off the features that it DOES understand and checking if any feature bits are remaining.

Cheers, Andreas

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