[RFC][PATCH 06/10] cifs: define inode-level cache object and register them

[Mingming Cao]

Steve French <smfrench at gmail.com> wrote on 06/25/2010 04:05:30 PM:

> Steve French <smfrench at gmail.com>
> 06/25/2010 04:05 PM
>
> To
>
> Jeff Layton <jlayton at samba.org>, "Aneesh Kumar K.V"
> <aneesh.kumar at linux.vnet.ibm.com>, Mingming Cao/Beaverton/IBM at IBMUS
>
> cc
>
> David Howells <dhowells at redhat.com>, Suresh Jayaraman
> <sjayaraman at suse.de>, linux-cifs at vger.kernel.org, linux-
> fsdevel at vger.kernel.org, linux-kernel at vger.kernel.org, samba-
> technical at lists.samba.org, Jeff Layton <jlayton at redhat.com>
>
> Subject
>
> Re: [RFC][PATCH 06/10] cifs: define inode-level cache object and
> register them
>
> On Fri, Jun 25, 2010 at 5:26 PM, Jeff Layton <jlayton at samba.org> wrote:
> >
> > On Fri, 25 Jun 2010 22:46:38 +0100
> > David Howells <dhowells at redhat.com> wrote:
> >
> > > Jeff Layton <jlayton at samba.org> wrote:
> > >
> > > > Looks like it mostly uses the ctime. IMO, the mtime would be a
better
> > > > choice since it changes less frequently, but I don't guess that it
> > > > matters very much.
> > >
> > > I'd've thought mtime changes more frequently since that's
> altered when data is
> > > written.  ctime is changed when attributes are changed.
> > >
> >
> > IIUC, updating mtime for a write is also an attribute change, and that
> > affects ctime. According to the stat(2) manpage:
> >
> >       The field st_ctime is changed by writing or by setting
>  inode  informa-
> >       tion (i.e., owner, group, link count, mode, etc.).
> >
> > > Note that Ext4 appears to have a file creation time field in its
inode
> > > (struct ext4_inode::i_crtime[_extra]).  Can Samba be made to use
that?
> > >
> >
> > Is it exposed to userspace in any (standard) way? It would be handy to
> > have that. While we're wishing...it might also be nice to have a
> > standard way to get at the i_generation from userspace too.
> >
>
> Yes - I have talked with MingMing and Aneesh about those (NFS may
> someday be able to use those too).  An obstacle in the past had been
> that samba server stores its own fake creation time in an ndr encoded
> xattr which complicates things.
>
> MingMing/Annesh -
> Xattr or other way to get at birth time?
>
>

Not yet,
 The ext4 file creation time only accesable from the kernel at the moment.
There were discussion
to make this information avaliable via xattr before, but was rejected,
since most people
agree that making this info avalibele via stat() is more standard. However
modifying stat() would imply
big interface change. thus no action has been taken yet.

> --
> Thanks,
>
> Steve