Date:	Tue, 24 Nov 2015 10:07:43 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Jan Kara <jack@...e.cz>, Shuichi Ihara <sihara@....com>,
	Li Xi <pkuelelixi@...il.com>,
	Andreas Dilger <adilger@...ger.ca>,
	Theodore Ts'o <tytso@....edu>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Дмитрий Монахов 
	<dmonakhov@...nvz.org>, Shuichi Ihara <ihashu@...il.com>
Subject: Re: [v15 0/4] ext4: add project quota support

On Tue 24-11-15 07:15:23, Dave Chinner wrote:
> On Mon, Nov 23, 2015 at 10:25:23AM +0100, Jan Kara wrote:
> > On Fri 20-11-15 08:47:27, Dave Chinner wrote:
> > > On Wed, Nov 18, 2015 at 02:14:32PM +0000, Shuichi Ihara wrote:
> > > > 
> > > > 11/9/15, 6:28 AM , "Dave Chinner" <david@...morbit.com> wrote:
> > > > 
> > > > >On Thu, Nov 05, 2015 at 03:13:10PM +0000, Shuichi Ihara wrote:
> > > > >> Hello Ted, Andreas,
> > > > >> 
> > > > >> Shilong posted an email here a week ago below.
> > > > >> http://lists.openwall.net/linux-ext4/2015/10/30/2
> > > > >> 
> > > > >> we identified 10 project quota related xfstest and ported them into ext4/xxx.
> > > > >> test number are 304, 305, 299, 244, 196, 134, 108, 107, 106, 050 in xfs.
> > > > >> 
> > > > >> 
> > > > >> We ported 9/10 tests into ext4/xxx
> > > > >> ext4/050 ext4/106 ext4/107 ext4/108 ext4/196 ext4/244 ext4/299 ext4/400 ext4/401
> > > > >
> > > > >Please make them generic tests - the ext4 project quota
> > > > >functioanlity should work with those tests being completely
> > > > >unchanged except for a "_requires_project_quota()" function...
> > > > 
> > > > Right now, we enhanced quotatool to support project quota and above project quota tests in ext4 uses that interface.
> > > > xfs uses own interface xfs_xx for project quota tests in xfs.
> > > > what interface are you looking at if we move ext4's project quota tests into generic tests?
> > > 
> > > The project quota support in the generic quota tool should work XFS
> > > as well as ext4. If it doesn't, then it's not a generic tool, right?
> > > The whole point of having ext4 use the same userspace API as XFS is
> > > so that all quotas can be managed with the one tool. Essentially, if
> > > ext4 project quotas cannot be controlled by xfs_quota, then the ext4
> > > code is not compatible with XFS and hence still needs work.
> > > 
> > > FWIW, if ext4 has implemented the kernel project quota interfaces
> > > correctly, then it should not matter whether we use xfs_quota or the
> > > generic quotatool because the kernel will translate the filesystem
> > > information to whatever format the quota was requested in...
> > > 
> > > So, you should be able to simply use the xfs_quota tool in the tests
> > > you make generic without needing any significant modification to the
> > > tests to run them on ext4. Yes, that may mean you need to send a 5
> > > line patch to make xfs_quota run on ext4, but that's trivial
> > > compared to duplicating >10 tests and then having to maintain them
> > > forever...
> > 
> > Yeah, last time I tried the only modification xfs_quota tool needed to work
> > correctly with ext4 was to remove / modify the check for filesystem type
> > in fs_table_initialise_mounts(). The question is how to properly deal with
> > that. I don't think just removing the fs type check is the right way to go
> > as that will have unexpected side effects for operations working on
> > "all" filesystems - currently these are restricted to "all" *XFS*
> > filesystems.
> > 
> > Maybe we can add a command line option which will disable the fs type check
> > so that non-XFS filesystems can be handled. We used to have an option like
> > this for xfs_io but it seems it got removed so I'm not sure we want to add
> > that into xfs_quota though. Dave?
> 
> The option is still there in xfs_io, we just ignore it because
> we do the detection automatically now via:
> 
>                 if (!platform_test_xfs_fd(c))
>                         flags |= IO_FOREIGN;
> 
> The rest of the libxcmd infrastructure handles enabling/disabling
> the commands for foreign filesystems  via the
> io/init.c::init_check_command() function, which does:
> 
>         if (file && !(ct->flags & CMD_FOREIGN_OK) &&
>                                         (file->flags & IO_FOREIGN)) {
>                 fprintf(stderr,
>         _("foreign file active, %s command is for XFS filesystems only\n"),
>                         ct->name);
>                 return 0;
>         }
> 
> 
> It is trivial to add this to xfs_quota (ok, it's 20 lines of code)
> and so allow the relevant commands the tests need to operate on
> foreign filesystems.

OK, then I agree that enabling xfs_quota to work for ext4 filesystems is
the easiest way to make xfstests project quota tests work for ext4.

For usability of project quota on ext4, we want the support in quota-tools
as soon as possible anyway but it is a separate issue...
	
								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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