Btrfs: free the stale device

When btrfs on a device is overwritten with a new btrfs (mkfs),
the old btrfs instance in the kernel becomes stale. So with this
patch, if kernel finds device is overwritten then delete the stale
fsid/uuid.

Signed-off-by: Anand Jain <anand.jain@oracle.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b851964b7345..ea293db89cc4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -445,6 +445,61 @@ static void pending_bios_fn(struct btrfs_work *work)
         run_scheduled_bios(device);
 }
 
+
+void btrfs_free_stale_device(struct btrfs_device *cur_dev)
+{
+        struct btrfs_fs_devices *fs_devs;
+        struct btrfs_device *dev;
+
+        if (!cur_dev->name)
+                return;
+
+        list_for_each_entry(fs_devs, &fs_uuids, list) {
+                int del = 1;
+
+                if (fs_devs->opened)
+                        continue;
+                if (fs_devs->seeding)
+                        continue;
+
+                list_for_each_entry(dev, &fs_devs->devices, dev_list) {
+
+                        if (dev == cur_dev)
+                                continue;
+                        if (!dev->name)
+                                continue;
+
+                        /*
+                         * Todo: This won't be enough. What if the same device
+                         * comes back (with new uuid and) with its mapper path?
+                         * But for now, this does help as mostly an admin will
+                         * either use mapper or non mapper path throughout.
+                         */
+                        rcu_read_lock();
+                        del = strcmp(rcu_str_deref(dev->name),
+                                                rcu_str_deref(cur_dev->name));
+                        rcu_read_unlock();
+                        if (!del)
+                                break;
+                }
+
+                if (!del) {
+                        /* delete the stale device */
+                        if (fs_devs->num_devices == 1) {
+                                btrfs_sysfs_remove_fsid(fs_devs);
+                                list_del(&fs_devs->list);
+                                free_fs_devices(fs_devs);
+                        } else {
+                                fs_devs->num_devices--;
+                                list_del(&dev->dev_list);
+                                rcu_string_free(dev->name);
+                                kfree(dev);
+                        }
+                        break;
+                }
+        }
+}
+
 /*
  * Add new device to list of registered devices
  *
@@ -560,6 +615,12 @@ static noinline int device_list_add(const char *path,
         if (!fs_devices->opened)
                 device->generation = found_transid;
 
+        /*
+         * if there is new btrfs on an already registered device,
+         * then remove the stale device entry.
+         */
+        btrfs_free_stale_device(device);
+
         *fs_devices_ret = fs_devices;
 
         return ret;