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    Subject[PATCH 09/34] union-mount: Add two superblock fields for union mounts
    Add two fields to struct super_block to support union mounts.
    s_union_lower_mnts is a pointer to a cloned vfsmount tree of all the
    lower (read-only) mounts unioned with the topmost (read-write)
    vfsmount. These mounts may have submounts which will also be unioned;
    hence we copy the entire vfsmount tree, not just the root vfsmounts.
    s_union_count is the number of lower mounts unioned at the root of the
    file system. This count is the maximum number of directories that
    will ever be unioned with a single directory. We use it to allocate a
    union stack of the correct size for each directory.

    Signed-off-by: Valerie Aurora <>
    include/linux/fs.h | 12 ++++++++++++
    1 files changed, 12 insertions(+), 0 deletions(-)

    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index 2e3d745..5e35b03 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1397,6 +1397,18 @@ struct super_block {
    * Decremented by free_vfsmnt() if MNT_HARD_READONLY is set.
    int s_hard_readonly_users;
    + /*
    + * Root of the private cloned vfsmount tree of the read-only
    + * mounts in this union (set in topmost vfsmount only)
    + */
    + struct vfsmount *s_union_lower_mnts;
    + /*
    + * Number of layers in this union, not counting the topmost or
    + * submounts.
    + */
    + unsigned int s_union_count;

    extern struct timespec current_fs_time(struct super_block *sb);

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      Last update: 2010-09-17 00:17    [W:0.019 / U:1.176 seconds]
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