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    SubjectRe: [RFC][PATCH 06/10] cifs: define inode-level cache object and register them
    Date
    On Fri, 25 Jun 2010 17:52:24 -0700, Mingming Cao <mcao@us.ibm.com> wrote:
    >
    >
    > Steve French <smfrench@gmail.com> wrote on 06/25/2010 04:05:30 PM:
    >
    > > Steve French <smfrench@gmail.com>
    > > 06/25/2010 04:05 PM
    > >
    > > To
    > >
    > > Jeff Layton <jlayton@samba.org>, "Aneesh Kumar K.V"
    > > <aneesh.kumar@linux.vnet.ibm.com>, Mingming Cao/Beaverton/IBM@IBMUS
    > >
    > > cc
    > >
    > > David Howells <dhowells@redhat.com>, Suresh Jayaraman
    > > <sjayaraman@suse.de>, linux-cifs@vger.kernel.org, linux-
    > > fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, samba-
    > > technical@lists.samba.org, Jeff Layton <jlayton@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@samba.org> wrote:
    > > >
    > > > On Fri, 25 Jun 2010 22:46:38 +0100
    > > > David Howells <dhowells@redhat.com> wrote:
    > > >
    > > > > Jeff Layton <jlayton@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.

    NFS ganesha pNFS also had a requirement for getting i_generation and
    inode number in userspace. So may be we should now look at updating
    stat or add a variant syscall that include i_generation and create time
    in the return value

    -aneesh
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