[PATCH 2/3] btrfs: volumes: Add btrfs_fs_devices::missing_list to collect missing devices

[Qu Wenruo <wqu@xxxxxxxx>]

This enables btrfs to iterate missing devices separately, without
iterating all fs_devices.

This provides the basis for later degraded chunk enhancement.

The change includes:
- Add missing devices to btrfs_fs_devices::missing_list
  This happens at add_missing_dev() and other locations where
  missing_devices get increased.

- Remove missing devices from btrfs_fs_devices::missing_list
  This needs to cover all locations where missing_devices get decreased.

Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
 fs/btrfs/volumes.c | 27 +++++++++++++++++++++------
 fs/btrfs/volumes.h |  6 ++++++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index eee5fc1d11f0..a462d8de5d2a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -324,6 +324,7 @@ static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid,
 
 	INIT_LIST_HEAD(&fs_devs->devices);
 	INIT_LIST_HEAD(&fs_devs->alloc_list);
+	INIT_LIST_HEAD(&fs_devs->missing_list);
 	INIT_LIST_HEAD(&fs_devs->fs_list);
 	if (fsid)
 		memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);
@@ -1089,6 +1090,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 		if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
 			fs_devices->missing_devices--;
 			clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+			list_del_init(&device->dev_alloc_list);
 		}
 	}
 
@@ -1250,11 +1252,10 @@ static void btrfs_close_one_device(struct btrfs_device *device)
 	if (device->bdev)
 		fs_devices->open_devices--;
 
+	list_del_init(&device->dev_alloc_list);
 	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
-	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
-		list_del_init(&device->dev_alloc_list);
+	    device->devid != BTRFS_DEV_REPLACE_DEVID)
 		fs_devices->rw_devices--;
-	}
 
 	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
 		fs_devices->missing_devices--;
@@ -2140,6 +2141,12 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
 		device->fs_devices->rw_devices--;
 		mutex_unlock(&fs_info->chunk_mutex);
 	}
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
+		mutex_lock(&fs_info->chunk_mutex);
+		list_del_init(&device->dev_alloc_list);
+		device->fs_devices->missing_devices--;
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
 
 	mutex_unlock(&uuid_mutex);
 	ret = btrfs_shrink_device(device, 0);
@@ -2184,9 +2191,6 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
 	if (cur_devices != fs_devices)
 		fs_devices->total_devices--;
 
-	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
-		cur_devices->missing_devices--;
-
 	btrfs_assign_next_active_device(device, NULL);
 
 	if (device->bdev) {
@@ -2236,6 +2240,13 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
 		device->fs_devices->rw_devices++;
 		mutex_unlock(&fs_info->chunk_mutex);
 	}
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
+		mutex_lock(&fs_info->chunk_mutex);
+		list_add(&device->dev_alloc_list,
+			 &fs_devices->missing_list);
+		device->fs_devices->missing_devices++;
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
 	goto out;
 }
 
@@ -2438,6 +2449,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
 	seed_devices->opened = 1;
 	INIT_LIST_HEAD(&seed_devices->devices);
 	INIT_LIST_HEAD(&seed_devices->alloc_list);
+	INIT_LIST_HEAD(&seed_devices->missing_list);
 	mutex_init(&seed_devices->device_list_mutex);
 
 	mutex_lock(&fs_devices->device_list_mutex);
@@ -6640,6 +6652,7 @@ static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices,
 	fs_devices->num_devices++;
 
 	set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+	list_add(&device->dev_alloc_list, &fs_devices->missing_list);
 	fs_devices->missing_devices++;
 
 	return device;
@@ -6979,6 +6992,7 @@ static int read_one_dev(struct extent_buffer *leaf,
 			 */
 			device->fs_devices->missing_devices++;
 			set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+			list_add(&device->dev_alloc_list, &fs_devices->missing_list);
 		}
 
 		/* Move the device to its own fs_devices */
@@ -6992,6 +7006,7 @@ static int read_one_dev(struct extent_buffer *leaf,
 
 			device->fs_devices->missing_devices--;
 			fs_devices->missing_devices++;
+			list_move(&device->dev_alloc_list, &fs_devices->missing_list);
 
 			device->fs_devices = fs_devices;
 		}
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index a7da1f3e3627..9cef4dc4b5be 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -253,6 +253,12 @@ struct btrfs_fs_devices {
 	 */
 	struct list_head alloc_list;
 
+	/*
+	 * Devices which can't be found. Projected by chunk_mutex.
+	 * This acts as a fallback allocation list for certain degraded mount.
+	 */
+	struct list_head missing_list;
+
 	struct btrfs_fs_devices *seed;
 	int seeding;
 
-- 
2.24.0