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    SubjectRe: [PATCH 2/5] VFS: Add VFS helper functions for setting up private namespaces
    Quoting Trond Myklebust (Trond.Myklebust@netapp.com):
    > On Tue, 2009-06-23 at 15:13 -0500, Serge E. Hallyn wrote:
    > > Quoting Trond Myklebust (Trond.Myklebust@netapp.com):
    > > > The purpose of this patch is to improve the remote mount path lookup
    > > > support for distributed filesystems such as the NFSv4 client.
    > > >
    > > > When given a mount command of the form "mount server:/foo/bar /mnt", the
    > > > NFSv4 client is required to look up the filehandle for "server:/", and
    > > > then look up each component of the remote mount path "foo/bar" in order
    > > > to find the directory that is actually going to be mounted on /mnt.
    > > > Following that remote mount path may involve following symlinks,
    > > > crossing server-side mount points and even following referrals to
    > > > filesystem volumes on other servers.
    > > >
    > > > Since the standard VFS path lookup code already supports walking paths
    > > > that contain all these features (using in-kernel automounts for
    > > > following referrals) we would like to be able to reuse that rather than
    > > > duplicate the full path traversal functionality in the NFSv4 client code.
    > > >
    > > > This patch therefore defines a VFS helper function create_mnt_ns(), that
    > > > sets up a temporary filesystem namespace and attaches a root filesystem to
    > > > it. It exports the create_mnt_ns() and put_mnt_ns() function for use by
    > > > filesystem modules.
    > > >
    > > > Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
    > >
    > > This looks good, thanks. Though I see no reason not to also switch over
    > > init_mount_tree() to the new helper.
    > >
    > > (Seems plausible that c/r code would use this as well)
    > >
    > > Reviewed-by: Serge Hallyn <serue@us.ibm.com>
    > >
    > > thanks,
    > > -serge
    >
    > Thanks for the review! I missed the code duplication in
    > init_mount_tree(). Something like the following?

    Yup.

    (it keeps bugging me that the order of args to list_add() gets reversed
    as a result, but clearly with both starting out empty it doesn't
    matter..)

    thanks,
    -serge

    > Cheers
    > Trond
    > --------------------------------------------------------------------
    > From: Trond Myklebust <Trond.Myklebust@netapp.com>
    > VFS: Switch init_mount_tree() to use the new create_mnt_ns() helper
    >
    > Eliminates some duplicated code...
    >
    > Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
    > ---
    >
    > fs/namespace.c | 11 ++---------
    > 1 files changed, 2 insertions(+), 9 deletions(-)
    >
    >
    > diff --git a/fs/namespace.c b/fs/namespace.c
    > index a7bea8c..4a86b85 100644
    > --- a/fs/namespace.c
    > +++ b/fs/namespace.c
    > @@ -2222,16 +2222,9 @@ static void __init init_mount_tree(void)
    > mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
    > if (IS_ERR(mnt))
    > panic("Can't create rootfs");
    > - ns = kmalloc(sizeof(*ns), GFP_KERNEL);
    > - if (!ns)
    > + ns = create_mnt_ns(mnt);
    > + if (IS_ERR(ns))
    > panic("Can't allocate initial namespace");
    > - atomic_set(&ns->count, 1);
    > - INIT_LIST_HEAD(&ns->list);
    > - init_waitqueue_head(&ns->poll);
    > - ns->event = 0;
    > - list_add(&mnt->mnt_list, &ns->list);
    > - ns->root = mnt;
    > - mnt->mnt_ns = ns;
    >
    > init_task.nsproxy->mnt_ns = ns;
    > get_mnt_ns(ns);
    >
    >
    > --
    > Trond Myklebust
    > Linux NFS client maintainer
    >
    > NetApp
    > Trond.Myklebust@netapp.com
    > www.netapp.com
    > --
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