nbd: add a flag to destroy an nbd device on disconnect

For ease of management it would be nice for users to specify that the
device node for a nbd device is destroyed once it is disconnected and
there are no more users.  Add a client flag and enable this operation to
happen.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 35 insertions, 1 deletions

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 4237e7286e99..b78f23ce2395 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -74,6 +74,7 @@ struct link_dead_args {
 #define NBD_HAS_PID_FILE                3
 #define NBD_HAS_CONFIG_REF              4
 #define NBD_BOUND                       5
+#define NBD_DESTROY_ON_DISCONNECT       6
 
 struct nbd_config {
         u32 flags;
@@ -174,6 +175,7 @@ static void nbd_dev_remove(struct nbd_device *nbd)
                 del_gendisk(disk);
                 blk_cleanup_queue(disk->queue);
                 blk_mq_free_tag_set(&nbd->tag_set);
+                disk->private_data = NULL;
                 put_disk(disk);
         }
         kfree(nbd);
@@ -1028,6 +1030,7 @@ static void nbd_config_put(struct nbd_device *nbd)
                         kfree(config->socks);
                 }
                 nbd_reset(nbd);
+
                 mutex_unlock(&nbd->config_lock);
                 nbd_put(nbd);
                 module_put(THIS_MODULE);
@@ -1539,6 +1542,7 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
         struct nbd_config *config;
         int index = -1;
         int ret;
+        bool put_dev = false;
 
         if (!netlink_capable(skb, CAP_SYS_ADMIN))
                 return -EPERM;
@@ -1633,6 +1637,15 @@ again:
         if (info->attrs[NBD_ATTR_SERVER_FLAGS])
                 config->flags =
                         nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
+        if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
+                u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
+                if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
+                        set_bit(NBD_DESTROY_ON_DISCONNECT,
+                                &config->runtime_flags);
+                        put_dev = true;
+                }
+        }
+
         if (info->attrs[NBD_ATTR_SOCKETS]) {
                 struct nlattr *attr;
                 int rem, fd;
@@ -1670,6 +1683,8 @@ out:
                 nbd_connect_reply(info, nbd->index);
         }
         nbd_config_put(nbd);
+        if (put_dev)
+                nbd_put(nbd);
         return ret;
 }
 
@@ -1722,6 +1737,7 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
         struct nbd_config *config;
         int index;
         int ret = -EINVAL;
+        bool put_dev = false;
 
         if (!netlink_capable(skb, CAP_SYS_ADMIN))
                 return -EPERM;
@@ -1773,6 +1789,18 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
                         nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
                 config->dead_conn_timeout *= HZ;
         }
+        if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
+                u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
+                if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
+                        if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
+                                              &config->runtime_flags))
+                                put_dev = true;
+                } else {
+                        if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
+                                               &config->runtime_flags))
+                                refcount_inc(&nbd->refs);
+                }
+        }
 
         if (info->attrs[NBD_ATTR_SOCKETS]) {
                 struct nlattr *attr;
@@ -1810,6 +1838,8 @@ out:
         mutex_unlock(&nbd->config_lock);
         nbd_config_put(nbd);
         nbd_put(nbd);
+        if (put_dev)
+                nbd_put(nbd);
         return ret;
 }
 
diff --git a/include/uapi/linux/nbd.h b/include/uapi/linux/nbd.h
index c91c642ea900..155e33f81913 100644
--- a/include/uapi/linux/nbd.h
+++ b/include/uapi/linux/nbd.h
@@ -37,7 +37,7 @@ enum {
         NBD_CMD_TRIM = 4
 };
 
-/* values for flags field */
+/* values for flags field, these are server interaction specific. */
 #define NBD_FLAG_HAS_FLAGS      (1 << 0) /* nbd-server supports flags */
 #define NBD_FLAG_READ_ONLY      (1 << 1) /* device is read-only */
 #define NBD_FLAG_SEND_FLUSH     (1 << 2) /* can flush writeback cache */
@@ -45,6 +45,10 @@ enum {
 #define NBD_FLAG_SEND_TRIM      (1 << 5) /* send trim/discard */
 #define NBD_FLAG_CAN_MULTI_CONN (1 << 8)        /* Server supports multiple connections per export. */
 
+/* These are client behavior specific flags. */
+#define NBD_CFLAG_DESTROY_ON_DISCONNECT (1 << 0) /* delete the nbd device on
+                                                    disconnect. */
+
 /* userspace doesn't need the nbd_device structure */
 
 /* These are sent over the network in the request/reply magic fields */