xfs_ioc_setlabel(
	struct file		*filp,
	struct xfs_mount	*mp,
	char			__user *newlabel)
{
	struct xfs_sb		*sbp = &mp->m_sb;
	char			label[XFSLABEL_MAX + 1];
	size_t			len;
	int			error;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	/*
	 * The generic ioctl allows up to FSLABEL_MAX chars, but XFS is much
	 * smaller, at 12 bytes.  We copy one more to be sure we find the
	 * (required) NULL character to test the incoming label length.
	 * NB: The on disk label doesn't need to be null terminated.
	 */
	if (copy_from_user(label, newlabel, XFSLABEL_MAX + 1))
		return -EFAULT;
	len = strnlen(label, XFSLABEL_MAX + 1);
	if (len > sizeof(sbp->sb_fname))
		return -EINVAL;

	error = mnt_want_write_file(filp);
	if (error)
		return error;

	spin_lock(&mp->m_sb_lock);
	memset(sbp->sb_fname, 0, sizeof(sbp->sb_fname));
	memcpy(sbp->sb_fname, label, len);
	spin_unlock(&mp->m_sb_lock);

	/*
	 * Now we do several things to satisfy userspace.
	 * In addition to normal logging of the primary superblock, we also
	 * immediately write these changes to sector zero for the primary, then
	 * update all backup supers (as xfs_db does for a label change), then
	 * invalidate the block device page cache.  This is so that any prior
	 * buffered reads from userspace (i.e. from blkid) are invalidated,
	 * and userspace will see the newly-written label.
	 */
	error = xfs_sync_sb_buf(mp);
	if (error)
		goto out;
	/*
	 * growfs also updates backup supers so lock against that.
	 */
	mutex_lock(&mp->m_growlock);
	error = xfs_update_secondary_sbs(mp);
	mutex_unlock(&mp->m_growlock);

	invalidate_bdev(mp->m_ddev_targp->bt_bdev);

out:
	mnt_drop_write_file(filp);
	return error;
}
Unknown