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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: Thu, 08 Mar 2012 17:41:16 -0600
Cc: Ben Myers <bpm@xxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>, "Josef 'Jeff' Sipek" <jeffpc@xxxxxxxxxxxxxx>
In-reply-to: <20120308233953.GP5091@dastard>
References: <4F5798F9.2050809@xxxxxxxxxx> <20120308013413.GL3592@dastard> <4F5813D8.8070305@xxxxxxxxxxx> <20120308153721.GS7762@xxxxxxx> <4F58D35D.7080504@xxxxxxxxxxx> <20120308163832.GV8545@xxxxxxx> <20120308233953.GP5091@dastard>
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On 3/8/12 5:39 PM, Dave Chinner wrote:
> On Thu, Mar 08, 2012 at 10:38:32AM -0600, Ben Myers wrote:
>> On Thu, Mar 08, 2012 at 09:42:21AM -0600, Eric Sandeen wrote:
>>> So, after thinking about this (and talking on irc) some more, I'm
>>> not convinced that a feature flag is the way to go.
>>> If we set a feature flag, suddenly old filesystems with 64-bit
>>> inodes will grow a new feature, and this will force a userspace
>>> upgrade - but there is no real new feature.  This seems like a bad
>>> idea.  My original patch (which Dave responded to with this one)
>>> simply made inode64 default, with no feature flags.
>>> Unless someone has a really compelling argument for the flag,
>>> I'm thinking this is the wrong approach after all.
>>> Perhaps I should resend the just-make-it-default patch.
>>> Comments?
>> Ew!  Forcing a userspace upgrade is not desireable.  Since we would only
>> want to set the feature bit if userspace were already upgraded, and only
>> if there are 64 bit inos...  How about two bits:  one is set by mkfs and
>> checked by the kernel to see if it is ok to set the other.  ;)
>> The first bit could also act as 'now its ok to default to inode64'.
> Too complex, IMO. Just add an xfs_admin command to set the inode64
> feature bit. That then overrides the inode64/inode32 mount option,
> and guarantees that the user has already upgraded userspace.
> i.e. the mount options are only valid if the feature bit it not set,
> and the feature bit can only be set via xfs_admin after a userspace
> upgrade. Kernels that don't understand the feature bit will refuse
> to mount, keeping in line with the current practise of requiring
> both kernel and userspace upgrades to occur in step to use new
> features....

Yep, I think that's the right path forward (had been thinking along
these lines too, today).


> Cheers,
> Dave.

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