Date: Wed, 15 Jul 2015 14:54:56 +1000
From: NeilBrown <neilb@suse.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: NeilBrown <neilb@suse.de>, "J. Bruce Fields" <bfields@fieldses.org>,
        John Stoffel <john@stoffel.org>,
        Austin S Hemmelgarn <ahferroin7@gmail.com>,
        Kevin Easton <kevin@guarana.org>, "Theodore Ts'o" <tytso@mit.edu>,
        Sage Weil <sage@newdream.net>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Dave Chinner <david@fromorbit.com>, Zach Brown <zab@redhat.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux API Mailing List <linux-api@vger.kernel.org>
Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag
Message-ID: <20150715145456.0376796b@noble>
In-Reply-To: <20150714131300.GA6804@amd>
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On Tue, 14 Jul 2015 15:13:00 +0200 Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
> 
> > BTW When you "swap" to a file the mtime doesn't get updated.  No one seems to
> > complain about that.  I guess it is a rather narrow use-case though.
> 
> Actually yes, I'd like to complain.
> 
> It was not swap, it was mount -o loop, but I guess that's the same
> case. Then rsync refused to work on that file... and being on slow ARM
> system it took me a while to figure out WTF is going on.
> 
> So yes, we have problems with mtime, and yes, they matter.
> 									Pavel

Odd...
I assume you mean
  mount -o loop /some/file  /mountpoint

and then when you write to the filesystem on /mountpoint the mtime
of /some/file doesn't get updated?
I think it should.
 drivers/block/loop.c uses vfs_iter_write() to write to a file.
 That calls f_op->write_iter which will typically call
 generic_file_write_iter() which will call file_update_time() to update
 the time stamps.

What filesystem was /some/file on?
I just did some testing on ext4 and it seems to do the right thing
mtime gets updated.

NeilBrown
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