Re: [PATCH 2/2] statx.2: add project support update

[Dave Chinner <david@fromorbit.com>]

On Mon, Mar 04, 2019 at 10:16:29PM +0100, Michael Kerrisk (man-pages) wrote:
> Hi Dave,
> On Mon, 4 Mar 2019 at 21:50, Dave Chinner <david@fromorbit.com> wrote:
> >
> > On Mon, Mar 04, 2019 at 02:52:59PM +0100, Michael Kerrisk (man-pages) wrote:
> > > Hello Wang Shilong,
> > >
> > > On Fri, 1 Mar 2019 at 15:06, Wang Shilong <wangshilong1991@gmail.com> wrote:
> > > >
> > > > From: Wang Shilong <wshilong@ddn.com>
> > >
> > > I take it that these patches relate to some API changes that are not
> > > yet merged into the kernel, right?
> > >
> > > Also, I think we need some accompanying info to describe project IDs.
> > > Can you point me at any documents/resources?
> >
> > Probably "best" documented in the man pages that ship with xfsprogs.
> 
> But, these IDs are a kernel construct, right?

On disk filesystem format construct, actually. The kernel doesn't
use them for anything other than filesystem quota accounting - it's
completely oblivious to the meaning of the IDs (unlike uids and gids
used for user and group quota accounting).

> Is their scope limited
> just to XFS, or do other filesystems have the concept also?

Originally only XFS. Irix implemented project quotas rather than
group quotas, IIRC, in the late 80s/early 90s(*) so XFS supported
project quotas for day zero. I think is was 2004/2005 that they were
fully supported on Linux (using an exclusive group or project
quota requirement) and with v5 filesystems we added a third quota
inode so we can have user, group and project quotas all active on a
filesystem at once.

2-3 years ago project quotas were added to ext4 and so anything that
uses the generic kernel quota infrastructure can implement it, too.

Cheers,

Dave.

(*) In some ways, we are still dragging Linux into the '80s, kicking
and screaming all the way :P

-- 
Dave Chinner
david@fromorbit.com