linux-kernel - RE: bcachefs

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Message-ID: <000901d7b3be$c7783120$56689360$@mindspring.com>
Date:   Mon, 27 Sep 2021 09:43:19 -0700
From:   "Frank Filz" <ffilzlnx@...dspring.com>
To:     "'Bernd Schubert'" <bernd.schubert@...tmail.fm>,
        "'Kent Overstreet'" <kent.overstreet@...il.com>,
        <linux-kernel@...r.kernel.org>, <linux-bcachefs@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>
Subject: RE: bcachefs - snapshots

> On 9/27/21 3:49 AM, Kent Overstreet wrote:
> > Snapshots have been merged! 9 months of work and 3k lines of new code,
> > finally released. Some highlights:
> >
> >  - btrfs style subvolumes & snapshots interface
> >  - snapshots are writeable
> >  - highly scalable: number of snapshots is limited only by your disk
> > space
> >  - highly space efficient: no internal fragmentation issues
> >
> > Design doc here: https://bcachefs.org/Snapshots/
> >
> > The core functionality is complete - snapshot creation and deletion
> > works, fsck changes are done (most of the complexity was in making
> > fsck work without O(number of snapshots) performance - tricky). Everything
> else is a todo item:
> >
> >  - still need to export different st_dev for files in different subvolumes
> >    (we'll never allocate a new inode with an inode number that collides with an
> >    inode inother subvolume - but snapshots will naturally result in colliding
> >    inode numbers)
> 
> With my limited high level view on it - shouldn't you discuss with Neil about a
> solution and to avoid going the btrfs route for colliding inode numbers?

I was going to ask that also having been watching the btrfs subvolume saga. As maintainer of the Ganesha user space NFS server I have an interest in this also though we haven't had anyone talk about bcachefs yet.

Frank