[PATCH 02/18] xstat: Add a pair of system calls to make extended file stats available [ver #6]
smfrench at gmail.com
Fri Aug 6 17:58:42 MDT 2010
On Fri, Aug 6, 2010 at 6:30 PM, Neil Brown <neilb at suse.de> wrote:
> On Thu, 5 Aug 2010 22:55:06 -0500
> Steve French <smfrench at gmail.com> wrote:
>> On Thu, Aug 5, 2010 at 10:38 PM, Neil Brown <neilb at suse.de> wrote:
>> > On Thu, 5 Aug 2010 16:52:18 -0700
>> > Jeremy Allison <jra at samba.org> wrote:
>> >> Don't add it as an EA. It's *not* an EA, it's a timestamp.
>> > I'm curious. Why do you particularly care what interface the kernel uses to
>> > provide you with access to this attribute?
>> > And given that it is an attribute that is not part of 'POSIX' or "UNIX", it
>> > would seem to be an extension - an extended attribute.
>> > As the Linux kernel does virtually nothing with this attribute except provide
>> > access, it seems to be a very different class of thing to other timestamps.
>> > Surely it is simply some storage associated with a file which is capable of
>> > storing a timestamp, which can be set or retrieved by an application, and
>> > which happens to be initialised to the current time when a file is created.
>> > Yes, to you it is a timestamp. But to Linux it is a few bytes of
>> > user-settable metadata. Sounds like an EA to me.
>> > Or do you really want something like BSD's 'btime' which as I understand it
>> > cannot be set. Would that be really useful to you?
>> Obviously the cifs and SMB2 protocols which Samba server support can
>> ask the server to set the create time of a file (this is handled
>> through xattrs today along with the "dos attribute" flags such as
>> archive/hidden/system), but certainly it is much more common (and
>> important) to read the creation time of an existing file.
> Just a point of clarification - when you say it is common and important to be
> able to read the creation time on an existing file, and you still talking in
> the context of cifs/smb windows compatibility, or are you talking in the
> broader context?
> If you are referring to a broader context could be please give more details
> because I have not heard any mention of any real value of creation-time out
> side of window interoperability - have such a use clearly documented would
> assist the conversation I think.
> If on the other hand you are just referring the the windows interoperability
> context ... given that you have to read an EA if the create-time has been
> changed, you will always have to read and EA so having something else is
> pointless ... or I'm missing something.
There are other cases, less common than cifs and smb2. One
that comes to mind is NFS version 4, but there are a few other
cases that I have heard of (backup/archive applications).
The RFC recommends that servers return attribute 50 (creation
time). See below text:
time_create 50 nfstime4 R/W The time of creation
of the object. This
attribute does not
have any relation to
the traditional UNIX
"ctime" or "change
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