[PATCH] ubifs: Add freeze support

[Hyunchul Lee]

and I missed the following case.

in some embedded systems, clean-up for shutdown should be fast.
during this clean-up, freeze file system to guarantee integrity.
umount with MNT_DETACH is not suitable because of not killing tasks.

On Mon, May 29, 2017 at 10:18:34AM +0900, Hyunchul Lee wrote:
> Hi, Richard.
> 
> On Fri, May 26, 2017 at 11:52:42AM +0200, Richard Weinberger wrote:
> > Hyunchul,
> > 
> > Am 26.05.2017 um 01:30 schrieb Hyunchul Lee:
> > > From: Hyunchul Lee <cheol.lee at lge.com>
> > > 
> > > for un/freeze support, implement freeze_super and un/freeze_fs
> > > of super_operations.
> > > ubifs_freeze_super just calls freeze_super. because freeze_super always
> > > succeeds if file system is read-only,  UBIFS errors should be checked.
> > > if there are errors, UBIFS is switched to read-only mode.
> > > ubifs_freeze_fs runs commit if TNC/LPT isn't clean. though all writes
> > > are blocked and sync_fs is called before, if commit alreay was started
> > > before writes are blocked, TNC/LPT might have dirty COW nodes.
> > 
> > you explain how you implement that feature, but not why.
> > What is the use-case?
> > I always thought this interface is only being used by LVM.
> 
> Sorry, I forgot this. I implement this to make a backup of some files, and
> support fsfreeze utility and SysRq's freeze/thaw commmand.
> 
> > 
> > Thanks,
> > //richard
> > 
> > ______________________________________________________
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> 
> -- 
> 
> Thanks,
> Hyunchul
> 
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-- 

Thanks,
Hyunchul