linux-kernel - Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6]

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Message-ID: <AANLkTimsjARdMfnvFRSyy6gakCtVhGRBbyauVTc_Cuwt@mail.gmail.com>
Date:	Thu, 22 Jul 2010 12:06:22 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Volker.Lendecke@...net.de, David Howells <dhowells@...hat.com>,
	Jan Engelhardt <jengelh@...ozas.de>,
	linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
	samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 02/18] xstat: Add a pair of system calls to make extended 
	file stats available [ver #6]

On Thu, Jul 22, 2010 at 11:47 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Thu, Jul 22, 2010 at 8:36 AM, Volker Lendecke
> <Volker.Lendecke@...net.de> wrote:
>>
>> The nice thing about this is also that if this is supposed
>> to be fully usable for Windows clients, the birthtime needs
>> to be changeable. That's what NTFS semantics gives you, thus
>> Windows clients tend to require it.
>
> Ok. So it's not really a creation date, exactly the same way ctime
> isn't at all a creation date.
>
> And maybe that actually hints at a better solution: maybe a better
> model is to create a new per-thread flag that says "do ctime updates
> the way windows does them".
>
> So instead of adding another "btime" - which isn't actually what even
> windows does - just admit that the _real_ issue is that Unix and
> Windows semantics are different for the pre-existing "ctime".
>
> The fact is, windows has "access time", "modification time" and
> "creation time" _exactly_ like UNIX. It's just that the ctime has
> slightly different semantics in windows vs unix. So quite frankly,
> it's totally insane to introduce a "birthtime", when that isn't even
> what windows wants, just because people cannot face the actual real
> difference.
>
> Tell me why we shouldn't just do this right?
>
>                Linus

I haven't been keeping up with this thread, but I believe NTFS has a
number of timestamps, not just 3.

This blog post references 8 in the left hand column.

The 4 standard (most common) ones are:

File last access
File last modified
File created
MFT last modified

My understanding is that "MFT last modified" has semantics very
similar to Linux ctime.

But there is not a generic equivalent to NTFS created.

Thus if trying to have the Linux kernel match NTFS semantics for the
benefit of Samba is the goal, it seems a new field should be preferred
instead of having linux ctime try to do different jobs.

Greg
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