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Re: [PATCH] default to 64 bit inodes & add feature flag

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] default to 64 bit inodes & add feature flag
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 07 Mar 2012 20:05:12 -0600
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>, "Josef 'Jeff' Sipek" <jeffpc@xxxxxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20120308013413.GL3592@dastard>
References: <4F5798F9.2050809@xxxxxxxxxx> <20120308013413.GL3592@dastard>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2
On 3/7/12 7:34 PM, Dave Chinner wrote:
> On Wed, Mar 07, 2012 at 11:20:57AM -0600, Eric Sandeen wrote:
>> From: Dave Chinner <dchinner@xxxxxxxxxx>
>>
>> Default to allowing 64-bit inodes on the filesystem.
>>
>> Add a feature bit to the the superblock to record whether 64 bit inodes have
>> been allocated on the filesystem or not. This allows us to reject mounting 
>> the
>> filesytem with inode32 if 64 bit inodes are present.
>>
>> Once a 64 bitinode is allocated, the inode64 superblock feature bit will be 
>> set.
>> Once the superblock feature bit is set, the filesystem will default to 64 bit
>> inodes regardless of whether inode64 is specified as a mount option.
>>
>> To ensure only 32 bit inodes are created, the inode32 mount option must be
>> used. If there are already 64 bit inodes as flagged by the superblock feature
>> bit, then the inode32 mount will be refused.
>>
>> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
>> ---
>>
>> Passing this along to revive the old discussion ... 
> 
> I have no objections to do this. However, the kernel patch is just
> the tip of the iceberg when it comes to implementing this.
> 
> Were there patches for userspace support of the feature bit? I don't
> recall if there were. I'm thinking that xfs_info needs to output
> whether this is set, which means the flag needs to be added to the
> xfs geometry ioctls in the kernel.

Nope, you just put this patch out as a suggestion, and pointed out
that userspace needed updates too.

If people are in agreement about this then we can proceed with the rest...

-Eric

> I'd also think that this should also be made a mkfs option (it will
> have to default to "not enabled" for a couple of years until distro
> kernels catch up) along with outputting the current value. This
> will then require xfstests mkfs filter changes, too.
> 
> We'll also need xfs_check, xfs_db (e.g. the version command) and
> xfs_repair knowledge of the new feature bit so they don't think the
> superblock is corrupted when this new bit gets set....


> Cheers,
> 
> Dave.

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