Re: [LSF/MM ATTEND] Stackable Union Filesystem Implementation

[Saket Sinha <saket.sinha89@gmail.com>]

On Thu, Jan 9, 2014 at 1:02 PM, J. R. Okajima <hooanon05g@gmail.com> wrote:
>
> Saket Sinha:
>> > For such purpose, a "block device level union" (instead of filesystem
>> > level union) may be an option for you, such as "dm snapshot".
>> >
>> I imagine that this would make things more complicated as ideally this
>> should be done in a filesystem driver. Again a "block device level
>> union" would all the more have lesser chances of getting this
>> filesystem driver included in the mainline kernel as kernel
>> maintainers prefer the drivers to be as simple as possible.
>
> ??
> I am afraid that I cannot fully understand what you wrote.

I am sorry for not explaining it properly. I was abrupt and hence was
misunderstood. My fault!.

> If you think "dm snapshot" does not exist currently, and you or someone
> else are going to develop a new feature, that is wrong. You already have
> "dm snapshot" feature and you can "stack" the block devices by using it.
> (cf. http://aufs.sourceforge.net/aufs2/report/sq/sq.pdf which is a bit
> old)
NO. I know it very much exists.  It forms the foundation of LVM2,
software RAIDs, dm-crypt disk encryption, and offers additional
features such as file system snapshots and I do not doubt either its
functionality or usage.

What I am referring here is the topic  <storing metadata in multiple
places vs  "block device level union">. See DM operates on block
device/sector, but a stackable filesystem operates on filesystem/file. My
point is this that which is the better approach according to the
kernel maintainers, so that this concept of Unioning gets universally
accepted and we have a mainline kernel union filesystem.

Regards,
Saket Sinha

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