Re: [PATCH] ubifs: Add freeze support

Hyunchul Lee
2017-05-30T02:38:05Z

On Mon, May 29, 2017 at 10:42:37AM +0200, Richard Weinberger wrote:
> Hyunchul,
>
> Am 29.05.2017 um 04:24 schrieb Hyunchul Lee:
> >>> This is just broken. First ubifs should still properly propagate
> >>> the errors, and second freezing/unfreezing read only file systems is
> >>> perfectly valid,
> >>
> >> it is right.
> >
> > if updating TNC is failed, ubifs might become inconsistant and be switched to
> > read-only mode. for example, when ubifs_jnl_update is called to create a file,
> > if inserting a znode for new inode is failed, TNC has only a znode for
> > new dentry. and this can be only recoverd by replay.
> >
> > is it required to fix this?
>
> UBIFS is designed to be power-cut tolerant.
> So, UBIFS must not corrupt in any case.
>
> Which failure are you facing?
>
> I have the feeling that you try to paper over some other issue. :-)

The failure hasn't happened. I wondered the following situation
should be handled.

ubifs_create
ubifs_jnl_update
write_head
ubifs_tnc_add_nm /* (1) add dentry to TNC */
ubifs_tnc_add /* (2) add new inode to TNC */
ubifs_tnc_add /* (3) add parent inode to TNC */

If ubifs_tnc_add(2) fails, TNC would have the index of a dentry
which points to an invalid inode. So, though ubifs_readdir
emits the dentry, this inode cannot be accessed. Becasue
there isn't the index of the inode.

I know this situation is hardly probable. But UBIFS would
be read-only and inconsitant in this situation, until replay
is completed.

>
> Thanks,
> //richard

--

Thanks,
Hyunchul