Re: [RFC 0/6] vfs: Add timestamp range check support

From: Dave Chinner <david@fromorbit.com>
To: "Theodore Ts'o" <tytso@mit.edu>,
	Deepa Dinamani <deepa.kernel@gmail.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	arnd@arndb.de, tglx@linutronix.de, gregkh@linuxfoundation.org,
	akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
	y2038@lists.linaro.org, linux-afs@lists.infradead.org,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	linux-ext4@vger.kernel.org
Subject: Re: [RFC 0/6] vfs: Add timestamp range check support
Date: Fri, 4 Nov 2016 10:48:02 +1100	[thread overview]
Message-ID: <20161103234802.GK14023@dastard> (raw)
In-Reply-To: <20161103204357.r7lgvbsv3euujijn@thunk.org>

On Thu, Nov 03, 2016 at 04:43:57PM -0400, Theodore Ts'o wrote:
> On Thu, Nov 03, 2016 at 09:48:27AM +1100, Dave Chinner wrote:
> > 
> > We're going to need regression tests for this to ensure that it
> > works properly and that we don't inadvertantly break it in future.
> > Can you write some xfstests that exercise this functionality and
> > validate that the mount behaviour, clamping and range limiting is
> > working as intended?
> 
> In order to have automated regression tests which are file system
> independent, we need a way to query what are the timestamps that a
> particular mounted file systme supports.

We don't need that - we simply code it directly into the test
infrastructure, like we've done for things like the maximum number
of ACLs a filesystem supports (common/attr::_acl_get_max()).

> The last option, which is admittedly ugly, would be to create an shell
> function which knows how to figure out the max_timestamp and
> min_timestamp by using the file system name and querying the
> superblock using dumpe2fs, xfs_db, etc.

Yup, precisely that. We shouldn't trust the kernel to tell us the
correct thing to enable the test that tells us that thing is working
correctly or not...

> I'd argue for the last option because once we do get a programmtic way
> to get the information via a system call such as fsinfo(2), we can
> convert xfstests to use it, where as if we add an ioctl to return this
> information, we'll have to support the ioctl forever.

We have to support kernels that won't ever have something like
fsinfo, so it has to be done the "ugly way".

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com