+/*
+ * Find a free minor number.
+ */
+minor_t
+zfsdev_minor_alloc(void)
+{
+ static minor_t last_minor;
+ minor_t m;
+
+ ASSERT(MUTEX_HELD(&zfsdev_state_lock));
+
+ for (m = last_minor + 1; m != last_minor; m++) {
+ if (m > ZFSDEV_MAX_MINOR)
+ m = 1;
+ if (ddi_get_soft_state(zfsdev_state, m) == NULL) {
+ last_minor = m;
+ return (m);
+ }
+ }
+
+ return (0);
+}
+
+static int
+zfs_ctldev_init(dev_t *devp)
+{
+ minor_t minor;
+ zfs_soft_state_t *zs;
+
+ ASSERT(MUTEX_HELD(&zfsdev_state_lock));
+ ASSERT(getminor(*devp) == 0);
+
+ minor = zfsdev_minor_alloc();
+ if (minor == 0)
+ return (ENXIO);
+
+ if (ddi_soft_state_zalloc(zfsdev_state, minor) != DDI_SUCCESS)
+ return (EAGAIN);
+
+ *devp = makedevice(getemajor(*devp), minor);
+
+ zs = ddi_get_soft_state(zfsdev_state, minor);
+ zs->zss_type = ZSST_CTLDEV;
+ zfs_onexit_init((zfs_onexit_t **)&zs->zss_data);
+
+ return (0);
+}
+
+static void
+zfs_ctldev_destroy(zfs_onexit_t *zo, minor_t minor)
+{
+ ASSERT(MUTEX_HELD(&zfsdev_state_lock));
+
+ zfs_onexit_destroy(zo);
+ ddi_soft_state_free(zfsdev_state, minor);
+}
+
+void *
+zfsdev_get_soft_state(minor_t minor, enum zfs_soft_state_type which)
+{
+ zfs_soft_state_t *zp;
+
+ zp = ddi_get_soft_state(zfsdev_state, minor);
+ if (zp == NULL || zp->zss_type != which)
+ return (NULL);
+
+ return (zp->zss_data);
+}
+
+static int
+zfsdev_open(dev_t *devp, int flag, int otyp, cred_t *cr)
+{
+ int error = 0;
+
+ if (getminor(*devp) != 0)
+ return (zvol_open(devp, flag, otyp, cr));
+
+ /* This is the control device. Allocate a new minor if requested. */
+ if (flag & FEXCL) {
+ mutex_enter(&zfsdev_state_lock);
+ error = zfs_ctldev_init(devp);
+ mutex_exit(&zfsdev_state_lock);
+ }
+
+ return (error);
+}
+
+static int
+zfsdev_close(dev_t dev, int flag, int otyp, cred_t *cr)
+{
+ zfs_onexit_t *zo;
+ minor_t minor = getminor(dev);
+
+ if (minor == 0)
+ return (0);
+
+ mutex_enter(&zfsdev_state_lock);
+ zo = zfsdev_get_soft_state(minor, ZSST_CTLDEV);
+ if (zo == NULL) {
+ mutex_exit(&zfsdev_state_lock);
+ return (zvol_close(dev, flag, otyp, cr));
+ }
+ zfs_ctldev_destroy(zo, minor);
+ mutex_exit(&zfsdev_state_lock);
+
+ return (0);
+}
+