On Thu 25-09-14 17:59:12, Dave Chinner wrote:

On Wed, Sep 24, 2014 at 07:01:05PM +0200, Jan Kara wrote:

quoted

On Wed 24-09-14 09:26:34, Christoph Hellwig wrote:

quoted

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

quoted

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.

  Do you mean full get/setfsxattr API?

That's a good start.

The bigger issue in my mind is that we already have a fully featured
quota API that supports project quotas and userspace tools available
that manipulate it. xfstests already uses those tools and API
for testing project quotas.

  Well, the VFS quota API is trivially extended by adding additional quota
type so I don't really see about which reinventing of quota API are you
speaking here...

This whole patchset reinvents all the quota APIs, and will require
adding support in userspace, and hence require re-inventing all the
test infrastructure we already have because it won't be compatible
with the existing project quota test code.

  Well, quota-tools will have to extended to know about the new quota type.
Yes. But that's easy to do. I think teaching xfs quota tools to work with
ext4 will be a bigger project plus I don't think I want to force sysadmins
which are used to work with quota-tools to switch to other utilities just
because of project quotas.

Regarding xfstests - I've checked and most of the project quota tests in
xfs directory aren't directly usable for ext4 anyway because of other
functionality ext4 doesn't support. So we'll need to distill the least
common denominator from them anyway...

quoted

  That basically contains project ID,
flags (those that are currently get/set with FS_IOC_GETFLAGS/SETFLAGS), and
extent size hint right?

It's a different set of flag definitions. We translate the interface
XFS_XFLAG_* values to/from the inode on-disk XFS_DIFLAG_* inode values, just
like we translate the VFS FS_*_FL flags that get passed through the
FS_IOC_GETFLAGS/SETFLAGS ioctl.

quoted

That seems workable and it would also make setting
of PROJINHERIT flag fs agnostic. Only we would have to create some generic
flags namespace and merge into that ext4 flags and have a translation
function for the old ext4 flags.

The XFS_XFLAGS_* are already filesystem agnostic - they are flags
that are only used for interfacing with userspace and hence only
exist at the ioctl copy in/out layer.....

quoted

Also I'm afraid we may quickly run out of
32 available flags in xflags so we'd need to extend that. But all this
seems to be doable.

The struct fsxattr was designed to be extensible - it has unused
padding and enough space in the flags field to allow us to
conditionally use that padding....

  Yeah, this should all be easy.

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR