Re: [PATCH v4] overlayfs: Provide mount options sync=off/fs to skip sync

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Jul 21, 2020 at 03:15:55PM +0200, Miklos Szeredi wrote:
> On Mon, Jul 20, 2020 at 6:16 PM Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > For building images containers folks need to sync upper layer. Their
> > current plan is to use "syncfs upper/" because it is same as if overlay
> > was mounted with sync=fs. But this syncs whole upper filesystem and
> > not just upper of a particular overlayfs instance
> >
> > So idea was to provide sync=fs from the beginning and ask container
> > folks to use this. So that in future if we can optimize sync=fs to
> > sync selctive inodes, then container runtime will automatically
> > benefit from it without any changes. It also reduces the chances
> > of error on container runtime which fail to sync upper.  Hence idea
> > of sync=fs sounded appleaing to me.
> 
> Not sure I understand the reason for sync=fs?  Should it rather be
> sync=shutdown?
> 
> >
> > Havid said that, I am open to dropping sync=fs for now, if you don't
> > see the value at this point of time.
> 
> At this point it doesn't add any usefulness, so let's just drop it.

Ok, Will drop it.

> 
> > >
> > > Naming: I'm not at all convinced by any name having "sync" in it.  I
> > > think "sync=no" is about the implementation, not the functionality,
> > > and so it's confusing. The functionality is better described by
> > > "volatile" or "temporary".   But I can live with sync=... if voted
> > > down.
> >
> > I am fine with the name "volatile/temporary" for sync=off.
> 
> How about needing "volatile" for all kinds of modes that reduce the
> normal durability/integrity guarantees.  Then additional "sync=foobar"
> option to control the details?

Sounds good. For now I will just implement "volatile" which is equivalent
of sync=off. One can implement "volatile,sync=shutdown" in future if
need be.

Thanks
Vivek