linux-ext4 - Re: [RFC][PATCH 0/6] Enhanced file stat system call

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Date:	Fri, 13 May 2016 17:08:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Sharpe <realrichardsharpe@...il.com>
Cc:	Steve French <smfrench@...il.com>,
	David Howells <dhowells@...hat.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-afs@...r.kernel.org,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	samba-technical <samba-technical@...ts.samba.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Deepa Dinamani <deepa.kernel@...il.com>
Subject: Re: [RFC][PATCH 0/6] Enhanced file stat system call

On Friday 13 May 2016 07:28:29 Richard Sharpe wrote:
> On Mon, May 9, 2016 at 6:09 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Thursday 05 May 2016 21:00:18 Steve French wrote:
> >> On Thu, May 5, 2016 at 5:54 PM, Steve French <smfrench@...il.com> wrote:
> >> > On Wed, May 4, 2016 at 8:46 AM, Arnd Bergmann <arnd@...db.de> wrote:
> >> >> I've discussed this with Deepa in the past, as she is driving the
> >> >> convertion of the inode timestamps to timespec64 now, and we will
> >> >> need a new version of utimensat for her work as well. I can see good
> >> >> reasons either way (allowing updates of btime or disallowing them).
> >> >
> >> It would help interop with Windows (and presumably Mac) if birth time can be
> >> updated
> >
> > Ok, thanks. That is certainly a good reason in favor.
> >
> > If nothing else comes up, I guess we can prepare a patch for a new
> > utimensat variant to do this and wait for more comments on that.

In the meantime I found this LWN article at https://lwn.net/Articles/397442/
Apparently there was a discussion about 6 years ago, without a real
conclusion.

> Isn't there also a strong case for a setattr call that allows us to
> atomically set a collection of attributes from userspace?
> 
> It would seem that network file systems (the clients) could use such features.

I had not heard of this before, but that is obviously another option.
Most of the attributes returned by xstat are read-only, but I guess
this would include uid, gid, {a,b,c,m}time and mode (but not size)
along with a 'valid' mask that decides what to set (as in notify_change),
right?

	Arnd
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