Re: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)

[Daniel Phillips]

On Tuesday 22 May 2001 22:10, Andreas Dilger wrote:
> Peter Braam writes:
> > File system journal recovery can corrupt a snapshot, because it
> > copies data that needs to be preserved in a snapshot. During
> > journal replay such data may be copied again, but the source can
> > have new data already.
>
> The way it is implemented in reiserfs is to wait for existing
> transactions to complete, entirely flush the journal and block all
> new transactions from starting.  Stephen implemented a journal flush
> API to do this for ext3, but the hooks to call it from LVM are not in
> place yet.  This way the journal is totally empty at the time the
> snapshot is done, so the read-only copy does not need to do journal
> recovery, so no problems can arise.

I suppose I'm just reiterating the obvious, but we should eventually
have a generic filesystem transaction API at the VFS level, once we
have enough data points to know what the One True API should be.

--
Daniel
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