From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Colin Ian King <colin.king@canonical.com>,
overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH 0/6] Sort out overlay layers and fs arrays
Date: Fri, 22 Nov 2019 11:31:55 +0200 [thread overview]
Message-ID: <CAOQ4uxi5QoV-WyY2rXhGpFoOfvcKh0Pm0tfU1vPvyk+rj0zCNQ@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxjMsv2vE5Nn5D8TNCFxaz8b4duyOLOiPpy4qd1bs3bdwQ@mail.gmail.com>
> > > I was also considering setting xino=on by default if xino_auto
> > > is enabled, because what have we got to loose?
> > >
> > > The inodes whose st_ino fit in lower bits (by far more common) will
> > > use overlay st_dev and the inodes whose st_ino overflow the lower bits
> > > will use pseudo_dev. Seems like a win-win situation, but I wanted to
> > > get your feedback on this before sending out a patch.
> > >
> >
> > Arrr.. yes, there is a catch.
> > Overflowing lower bits has a price beyond just using pseudo_dev.
> > It introduces the possibility of inode number conflicts on directories,
> > because directories never use pseudo_dev.
> >
>
> But we could mitigate that problem if we reserve an fsid for volatile
> directory inode numbers. get_next_ino is 32bit anyway.
> I am going to take a swing at having xino=auto always enabling xino.
>
FWIW, pushed WIP branch to:
https://github.com/amir73il/linux/commits/ovl-ino
It is based on an updated ovl-layers branch of the $SUBJECT series.
During cleanup, I've found several corner cases bugs of setting
i_ino value and fixed them.
None of those bugs are critical.
AFAIK, the only user that complained on inconsistent i_ino is
an xfstest that is checking ino in /proc/locks.
However, I do think that the cleanup I made simplifies the code
which was a bit spaghetti in that area and with some more TLC
we can get to enabling xino from xino=auto even for filesystems
that have seldom high ino bits.
That could be a real benefit, because it is unlikely that users
will have enough knowledge or certainty about underlying fs
to declare xino=on.
I need to clear up some time to test i_ino changes and
the collision avoidance code, but for now, at least the ovl-ino branch
passes the existing regression tests.
Thanks,
Amir.
next prev parent reply other threads:[~2019-11-22 9:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-17 15:43 [PATCH 0/6] Sort out overlay layers and fs arrays Amir Goldstein
2019-11-17 15:43 ` [PATCH 1/6] ovl: fix corner case of non-unique st_dev;st_ino Amir Goldstein
2019-11-17 15:43 ` [PATCH 2/6] ovl: generalize the lower_layers[] array Amir Goldstein
2019-11-17 15:43 ` [PATCH 3/6] ovl: simplify ovl_same_sb() helper Amir Goldstein
2019-11-17 15:43 ` [PATCH 4/6] ovl: generalize the lower_fs[] array Amir Goldstein
2019-11-18 17:01 ` Amir Goldstein
2019-11-17 15:43 ` [PATCH 5/6] ovl: fix corner case of conflicting lower layer uuid Amir Goldstein
2019-11-17 15:43 ` [PATCH 6/6] ovl: fix corner case of non-constant st_dev;st_ino Amir Goldstein
2019-11-18 6:03 ` [PATCH 0/6] Sort out overlay layers and fs arrays Amir Goldstein
2019-11-18 7:57 ` Amir Goldstein
2019-11-22 9:31 ` Amir Goldstein [this message]
2019-11-25 14:45 ` Amir Goldstein
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