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    Subject[PATCH 35/73] union-mount: Create prepare_mnt_union() and cleanup_mnt_union() [ver #2]
    Date
    From: Valerie Aurora <vaurora@redhat.com>

    prepare_mnt_union() ties together all the mount-time checks and setup
    for union mounts. It tests the layers for suitability and builds the
    root union stack.

    cleanup_mnt_union() unwinds everything prepare_mnt_union() does.

    Original-author: Valerie Aurora <vaurora@redhat.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    ---

    fs/namespace.c | 40 ++++++++++++++++++++++++++++++++++++++++
    1 files changed, 40 insertions(+), 0 deletions(-)

    diff --git a/fs/namespace.c b/fs/namespace.c
    index 3355b99..261944d 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -1569,6 +1569,46 @@ out:
    return err;
    }

    +/**
    + * prepare_mnt_union - do setup necessary for a union mount
    + * @topmost_mnt: vfsmount of topmost layer
    + * @mntpnt: path of requested mountpoint
    + *
    + * We union every underlying file system that is mounted on the same mountpoint
    + * (well, pathname), read-only, and not shared. If we get at least one layer,
    + * we don't return an error, although we will complain in the kernel log if we
    + * hit a mount that can't be unioned.
    + *
    + * Caller needs namespace_sem, but can't have vfsmount_lock.
    + */
    +static int prepare_mnt_union(struct vfsmount *topmost_mnt, struct path *mntpnt)
    +{
    + int err;
    +
    + err = check_topmost_union_mnt(topmost_mnt, topmost_mnt->mnt_flags);
    + if (err)
    + return err;
    +
    + err = clone_union_tree(real_mount(topmost_mnt), mntpnt);
    + if (err)
    + return err;
    +
    + err = build_root_union(topmost_mnt);
    + if (err)
    + goto out;
    + return 0;
    +
    +out:
    + put_union_sb(topmost_mnt->mnt_sb);
    + return err;
    +}
    +
    +static void cleanup_mnt_union(struct vfsmount *topmost_mnt)
    +{
    + d_free_unions(topmost_mnt->mnt_root);
    + put_union_sb(topmost_mnt->mnt_sb);
    +}
    +
    /*
    * @source_mnt : mount tree to be attached
    * @nd : place the mount tree @source_mnt is attached


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