Re: UBIFS quota support

[Richard Weinberger <richard@nod.at>]

Sascha,

Am Mittwoch, 23. Januar 2019, 10:55:35 CET schrieb Sascha Hauer:
> > > S_SYNC won't help us. We need to make sure that a change of an inode and
> > > the corresponding update to the quota file is done atomically. Otherwise
> > > it may happen that we only change the size of an inode, but miss the
> > > corresponding quota updates, or depending on the implementation, maybe
> > > the other way round.
> > 
> > This is why I said yesterday you need to touch the UBIFS journal replay code too.
> > So, S_SYNC is not to keep the quota file consistent with UBIFS' state, it is
> > to make sure we don't lose quota updates.
> 
> But how we handle a power cut between the update to the quota file and
> the actual inode change then? During replay we'll find quota updates and
> inode updates, but we do not have any information which quota update
> belongs to which inode change.

In worst case we need to store more info in the journal to get this infos.
That's why I asked Jan for more info. I don't know what exactly quota expects
from the filesystem in terms of consistency. Maybe there are already some helpers, etc...

Thanks,
//richard