On Wed, Sep 24, 2014 at 06:25:07PM +0200, Jan Kara wrote:

On Wed 24-09-14 22:04:30, Li Xi wrote:

quoted

This patch adds ioctl interface for setting/getting project of ext4.

  The patch looks good to me. I was just wondering whether it won't be
useful to add an ioctl() which isn't ext4 specific. We could just extend
->setattr() to allow setting of project ID (most filesystems would just
return -EOPNOTSUPP but ext4 and xfs could do the right thing) and then call
->setattr from the generic ioctl. That way userspace won't have to care
about filesystem type when setting project ID... What do others think?

Absolutely.  In general I also wonder why this patch doesn't implement
the full XFS API.  Maybe there is a reason it was considered and
rejected, but it would be helpful to document why.