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SubjectRe: sget() misuse in nilfs
On Wed, 06 May 2009 15:28:59 +0900 (JST), Ryusuke Konishi wrote:
> If we treat read-only mount as the latest snapshot at the time (though
> we didn't take this interpretation), the transitions can be reduced
> to:
> * r/w -> r/w. Allowed.
> * r/w -> snapshot. Allowed if no checkpoint number was given (or the
> latest checkpoint was specified)
> * snapshot -> r/w. Allowed if it's the latest one and no r/w is there.
> * snapshot -> snapshot. Only if it's the same.
> Right?

Ah, I had forgotten garbage collection (GC).

GC can break checkpoints which are not marked as snapshot. ro-mount
cannot coexist with rw-mount because GC works while an rw-mount is

Sorry, the above interpretation was not easily realized.

> But it still needs test_exclusive_mount().
> The test_exclusive_mount() may be eliminable by adding rw-mount-exists
> flag on the_nilfs struct. I'll take some thinking.

The elimination of test_exclusive_mount() was possible by this method
if we can treat ro-mount as the latest checkpoint at the time.

I'd like to consider if a similiar elimination is possible in case
that ro-mount and rw-mount cannot coexist.

Ryusuke Konishi

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