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    Subject[PATCH 64/73] union-mount: Implement union-aware truncate() [ver #2]
    Date
    Original-author: Valerie Aurora <vaurora@redhat.com>
    Signed-off-by: David Howells <dhowells@redhat.com> (Further development)
    ---

    fs/open.c | 44 ++++++++++++++++++++++++++++++++++++++------
    1 files changed, 38 insertions(+), 6 deletions(-)

    diff --git a/fs/open.c b/fs/open.c
    index bce645b..f61183b 100644
    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -65,14 +65,17 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
    static long do_sys_truncate(const char __user *pathname, loff_t length)
    {
    struct path path;
    + struct nameidata nd;
    + struct vfsmount *mnt;
    struct inode *inode;
    + char *tmp;
    int error;

    error = -EINVAL;
    if (length < 0) /* sorry, but loff_t says... */
    goto out;

    - error = user_path(pathname, &path);
    + error = user_path_nd(AT_FDCWD, pathname, 0, &nd, &path, &tmp);
    if (error)
    goto out;
    inode = path.dentry->d_inode;
    @@ -86,18 +89,45 @@ static long do_sys_truncate(const char __user *pathname, loff_t length)
    if (!S_ISREG(inode->i_mode))
    goto dput_and_out;

    - error = mnt_want_write(path.mnt);
    + /* If we're looking at the lower layer of a union mount, then we need
    + * to create the file on the upperfs and truncate that.
    + */
    + if (IS_MNT_LOWER(path.mnt))
    + mnt = nd.path.mnt;
    + else
    + mnt = path.mnt;
    +
    + error = mnt_want_write(mnt);
    if (error)
    goto dput_and_out;

    - error = inode_permission(inode, MAY_WRITE);
    - if (error)
    - goto mnt_drop_write_and_out;
    + if (unlikely(IS_MNT_UNION(mnt))) {
    + /* We have to be able to write to the upperfs. */
    + error = -EROFS;
    + if (mnt->mnt_sb->s_flags & MS_RDONLY)
    + goto mnt_drop_write_and_out;
    +
    + /* But the lowerfs inode must offer write permission - if the
    + * lowerfs was mounted writably. */
    + error = __inode_permission(inode, MAY_WRITE);
    + if (error)
    + goto mnt_drop_write_and_out;
    + } else {
    + error = inode_permission(inode, MAY_WRITE);
    + if (error)
    + goto mnt_drop_write_and_out;
    + }

    error = -EPERM;
    if (IS_APPEND(inode))
    goto mnt_drop_write_and_out;

    + error = union_copyup_len(&nd, &path, length);
    + if (error)
    + goto mnt_drop_write_and_out;
    +
    + /* path may have changed after copyup */
    + inode = path.dentry->d_inode;
    error = get_write_access(inode);
    if (error)
    goto mnt_drop_write_and_out;
    @@ -119,9 +149,11 @@ static long do_sys_truncate(const char __user *pathname, loff_t length)
    put_write_and_out:
    put_write_access(inode);
    mnt_drop_write_and_out:
    - mnt_drop_write(path.mnt);
    + mnt_drop_write(mnt);
    dput_and_out:
    path_put(&path);
    + path_put(&nd.path);
    + putname(tmp);
    out:
    return error;
    }


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