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

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Message-ID: <20161103204357.r7lgvbsv3euujijn@thunk.org>
Date:   Thu, 3 Nov 2016 16:43:57 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Dave Chinner <david@...morbit.com>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de, tglx@...utronix.de, gregkh@...uxfoundation.org,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        y2038@...ts.linaro.org, linux-afs@...ts.infradead.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org
Subject: Re: [RFC 0/6] vfs: Add timestamp range check support

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.  One approach would be to use
fsinfo, which David Howells had been working on, but which has been
bike-shedded to death for the last n years, and I'd hate to block this
patch series behind a proposed new fsinfo(2) system call.
Alternatively, we can just create a specialized ioctl to return that
information which is non-ideal in other dimensions.

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.

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.

Does this make sense?   Any objections?

Cheers,

						- Ted