Btrfs: Add mount -o degraded to allow mounts to continue with missing devices

Signed-off-by: Chris Mason <chris.mason@oracle.com>

6 files changed, 253 insertions, 109 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 6c2c2c4e4d2a..a9377fb16c37 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -657,6 +657,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_NODATACOW           (1 << 1)
 #define BTRFS_MOUNT_NOBARRIER           (1 << 2)
 #define BTRFS_MOUNT_SSD                 (1 << 3)
+#define BTRFS_MOUNT_DEGRADED            (1 << 4)
 
 #define btrfs_clear_opt(o, opt)         ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)           ((o) |= BTRFS_MOUNT_##opt)
@@ -1606,4 +1607,6 @@ int btrfs_delete_xattrs(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, struct inode *inode);
 /* super.c */
 u64 btrfs_parse_size(char *str);
+int btrfs_parse_options(char *options, struct btrfs_root *root,
+                        char **subvol_name);
 #endif
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 574b1245964e..38b0d9ecda6a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -614,21 +614,6 @@ int readahead_tree_block(struct btrfs_root *root, u64 bytenr, u32 blocksize,
         return ret;
 }
 
-static int close_all_devices(struct btrfs_fs_info *fs_info)
-{
-        struct list_head *list;
-        struct list_head *next;
-        struct btrfs_device *device;
-
-        list = &fs_info->fs_devices->devices;
-        list_for_each(next, list) {
-                device = list_entry(next, struct btrfs_device, dev_list);
-                close_bdev_excl(device->bdev);
-                device->bdev = NULL;
-        }
-        return 0;
-}
-
 struct extent_buffer *btrfs_find_tree_block(struct btrfs_root *root,
                                             u64 bytenr, u32 blocksize)
 {
@@ -927,6 +912,8 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
 
         list_for_each(cur, &info->fs_devices->devices) {
                 device = list_entry(cur, struct btrfs_device, dev_list);
+                if (!device->bdev)
+                        continue;
                 bdi = blk_get_backing_dev_info(device->bdev);
                 if (bdi && bdi_congested(bdi, bdi_bits)) {
                         ret = 1;
@@ -1140,7 +1127,8 @@ static void btrfs_async_submit_work(struct work_struct *work)
 }
 
 struct btrfs_root *open_ctree(struct super_block *sb,
-                              struct btrfs_fs_devices *fs_devices)
+                              struct btrfs_fs_devices *fs_devices,
+                              char *options)
 {
         u32 sectorsize;
         u32 nodesize;
@@ -1276,12 +1264,19 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         if (!btrfs_super_root(disk_super))
                 goto fail_sb_buffer;
 
-        if (btrfs_super_num_devices(disk_super) != fs_devices->num_devices) {
+        btrfs_parse_options(options, tree_root, NULL);
+
+        if (btrfs_super_num_devices(disk_super) > fs_devices->num_devices) {
                 printk("Btrfs: wanted %llu devices, but found %llu\n",
                        (unsigned long long)btrfs_super_num_devices(disk_super),
                        (unsigned long long)fs_devices->num_devices);
-                goto fail_sb_buffer;
+                if (btrfs_test_opt(tree_root, DEGRADED))
+                        printk("continuing in degraded mode\n");
+                else {
+                        goto fail_sb_buffer;
+                }
         }
+
         fs_info->bdi.ra_pages *= btrfs_super_num_devices(disk_super);
 
         nodesize = btrfs_super_nodesize(disk_super);
@@ -1329,6 +1324,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         ret = btrfs_read_chunk_tree(chunk_root);
         BUG_ON(ret);
 
+        btrfs_close_extra_devices(fs_devices);
+
         blocksize = btrfs_level_size(tree_root,
                                      btrfs_super_root_level(disk_super));
 
@@ -1374,7 +1371,7 @@ fail_sb_buffer:
 fail_iput:
         iput(fs_info->btree_inode);
 fail:
-        close_all_devices(fs_info);
+        btrfs_close_devices(fs_info->fs_devices);
         btrfs_mapping_tree_free(&fs_info->mapping_tree);
 
         kfree(extent_root);
@@ -1429,6 +1426,13 @@ int write_all_supers(struct btrfs_root *root)
         dev_item = &sb->dev_item;
         list_for_each(cur, head) {
                 dev = list_entry(cur, struct btrfs_device, dev_list);
+                if (!dev->bdev) {
+                        total_errors++;
+                        continue;
+                }
+                if (!dev->in_fs_metadata)
+                        continue;
+
                 btrfs_set_stack_device_type(dev_item, dev->type);
                 btrfs_set_stack_device_id(dev_item, dev->devid);
                 btrfs_set_stack_device_total_bytes(dev_item, dev->total_bytes);
@@ -1482,6 +1486,11 @@ int write_all_supers(struct btrfs_root *root)
 
         list_for_each(cur, head) {
                 dev = list_entry(cur, struct btrfs_device, dev_list);
+                if (!dev->bdev)
+                        continue;
+                if (!dev->in_fs_metadata)
+                        continue;
+
                 BUG_ON(!dev->pending_io);
                 bh = dev->pending_io;
                 wait_on_buffer(bh);
@@ -1631,7 +1640,7 @@ int close_ctree(struct btrfs_root *root)
                 kfree(hasher);
         }
 #endif
-        close_all_devices(fs_info);
+        btrfs_close_devices(fs_info->fs_devices);
         btrfs_mapping_tree_free(&fs_info->mapping_tree);
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,23)
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 30d1ed293c25..2bc64fefe6ea 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -33,7 +33,8 @@ struct extent_buffer *btrfs_find_create_tree_block(struct btrfs_root *root,
 int clean_tree_block(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root, struct extent_buffer *buf);
 struct btrfs_root *open_ctree(struct super_block *sb,
-                              struct btrfs_fs_devices *fs_devices);
+                              struct btrfs_fs_devices *fs_devices,
+                              char *options);
 int close_ctree(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 020e5a83e31f..273a5b511f50 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -65,11 +65,13 @@ static void btrfs_put_super (struct super_block * sb)
 }
 
 enum {
-        Opt_subvol, Opt_nodatasum, Opt_nodatacow, Opt_max_extent,
-        Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd, Opt_err,
+        Opt_degraded, Opt_subvol, Opt_nodatasum, Opt_nodatacow,
+        Opt_max_extent, Opt_max_inline, Opt_alloc_start, Opt_nobarrier,
+        Opt_ssd, Opt_err,
 };
 
 static match_table_t tokens = {
+        {Opt_degraded, "degraded"},
         {Opt_subvol, "subvol=%s"},
         {Opt_nodatasum, "nodatasum"},
         {Opt_nodatacow, "nodatacow"},
@@ -106,9 +108,8 @@ u64 btrfs_parse_size(char *str)
         return res;
 }
 
-static int parse_options (char * options,
-                          struct btrfs_root *root,
-                          char **subvol_name)
+int btrfs_parse_options(char *options, struct btrfs_root *root,
+                        char **subvol_name)
 {
         char * p;
         struct btrfs_fs_info *info = NULL;
@@ -135,6 +136,12 @@ static int parse_options (char * options,
 
                 token = match_token(p, tokens, args);
                 switch (token) {
+                case Opt_degraded:
+                        if (info) {
+                                printk("btrfs: allowing degraded mounts\n");
+                                btrfs_set_opt(info->mount_opt, DEGRADED);
+                        }
+                        break;
                 case Opt_subvol:
                         if (subvol_name) {
                                 *subvol_name = match_strdup(&args[0]);
@@ -234,7 +241,7 @@ static int btrfs_fill_super(struct super_block * sb,
         sb->s_xattr = btrfs_xattr_handlers;
         sb->s_time_gran = 1;
 
-        tree_root = open_ctree(sb, fs_devices);
+        tree_root = open_ctree(sb, fs_devices, (char *)data);
 
         if (IS_ERR(tree_root)) {
                 printk("btrfs: open_ctree failed\n");
@@ -267,8 +274,6 @@ static int btrfs_fill_super(struct super_block * sb,
                 goto fail_close;
         }
 
-        parse_options((char *)data, tree_root, NULL);
-
         /* this does the super kobj at the same time */
         err = btrfs_sysfs_add_super(tree_root->fs_info);
         if (err)
@@ -341,7 +346,7 @@ int btrfs_get_sb_bdev(struct file_system_type *fs_type,
         if (error)
                 return error;
 
-        bdev = fs_devices->lowest_bdev;
+        bdev = fs_devices->latest_bdev;
         btrfs_lock_volumes();
         s = sget(fs_type, btrfs_test_super, set_anon_super, fs_devices);
         btrfs_unlock_volumes();
@@ -411,7 +416,7 @@ static int btrfs_get_sb(struct file_system_type *fs_type,
         int ret;
         char *subvol_name = NULL;
 
-        parse_options((char *)data, NULL, &subvol_name);
+        btrfs_parse_options((char *)data, NULL, &subvol_name);
         ret = btrfs_get_sb_bdev(fs_type, flags, dev_name, data, mnt,
                         subvol_name ? subvol_name : "default");
         if (subvol_name)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5fc7fb481474..43f74d17bcea 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -73,6 +73,7 @@ int btrfs_cleanup_fs_uuids(void)
                                 close_bdev_excl(dev->bdev);
                         }
                         list_del(&dev->dev_list);
+                        kfree(dev->name);
                         kfree(dev);
                 }
         }
@@ -127,7 +128,6 @@ static int device_list_add(const char *path,
                 memcpy(fs_devices->fsid, disk_super->fsid, BTRFS_FSID_SIZE);
                 fs_devices->latest_devid = devid;
                 fs_devices->latest_trans = found_transid;
-                fs_devices->lowest_devid = (u64)-1;
                 fs_devices->num_devices = 0;
                 device = NULL;
         } else {
@@ -159,13 +159,35 @@ static int device_list_add(const char *path,
                 fs_devices->latest_devid = devid;
                 fs_devices->latest_trans = found_transid;
         }
-        if (fs_devices->lowest_devid > devid) {
-                fs_devices->lowest_devid = devid;
-        }
         *fs_devices_ret = fs_devices;
         return 0;
 }
 
+int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
+{
+        struct list_head *head = &fs_devices->devices;
+        struct list_head *cur;
+        struct btrfs_device *device;
+
+        mutex_lock(&uuid_mutex);
+again:
+        list_for_each(cur, head) {
+                device = list_entry(cur, struct btrfs_device, dev_list);
+                if (!device->in_fs_metadata) {
+printk("getting rid of extra dev %s\n", device->name);
+                        if (device->bdev)
+                                close_bdev_excl(device->bdev);
+                        list_del(&device->dev_list);
+                        list_del(&device->dev_alloc_list);
+                        fs_devices->num_devices--;
+                        kfree(device->name);
+                        kfree(device);
+                        goto again;
+                }
+        }
+        mutex_unlock(&uuid_mutex);
+        return 0;
+}
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 {
         struct list_head *head = &fs_devices->devices;
@@ -179,6 +201,7 @@ int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
                         close_bdev_excl(device->bdev);
                 }
                 device->bdev = NULL;
+                device->in_fs_metadata = 0;
         }
         mutex_unlock(&uuid_mutex);
         return 0;
@@ -199,6 +222,9 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                 if (device->bdev)
                         continue;
 
+                if (!device->name)
+                        continue;
+
                 bdev = open_bdev_excl(device->name, flags, holder);
 
                 if (IS_ERR(bdev)) {
@@ -209,10 +235,8 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                 set_blocksize(bdev, 4096);
                 if (device->devid == fs_devices->latest_devid)
                         fs_devices->latest_bdev = bdev;
-                if (device->devid == fs_devices->lowest_devid) {
-                        fs_devices->lowest_bdev = bdev;
-                }
                 device->bdev = bdev;
+                device->in_fs_metadata = 0;
 
         }
         mutex_unlock(&uuid_mutex);
@@ -439,7 +463,8 @@ int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,
         }
         BUG_ON(ret);
 
-        device->bytes_used -= btrfs_dev_extent_length(leaf, extent);
+        if (device->bytes_used > 0)
+                device->bytes_used -= btrfs_dev_extent_length(leaf, extent);
         ret = btrfs_del_item(trans, root, path);
         BUG_ON(ret);
 
@@ -460,6 +485,7 @@ int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
         struct extent_buffer *leaf;
         struct btrfs_key key;
 
+        WARN_ON(!device->in_fs_metadata);
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
@@ -674,8 +700,6 @@ static int btrfs_rm_dev_item(struct btrfs_root *root,
 
         next_dev = list_entry(fs_devices->devices.next, struct btrfs_device,
                               dev_list);
-        if (bdev == fs_devices->lowest_bdev)
-                fs_devices->lowest_bdev = next_dev->bdev;
         if (bdev == root->fs_info->sb->s_bdev)
                 root->fs_info->sb->s_bdev = next_dev->bdev;
         if (bdev == fs_devices->latest_bdev)
@@ -698,7 +722,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 {
         struct btrfs_device *device;
         struct block_device *bdev;
-        struct buffer_head *bh;
+        struct buffer_head *bh = NULL;
         struct btrfs_super_block *disk_super;
         u64 all_avail;
         u64 devid;
@@ -712,47 +736,73 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
                 root->fs_info->avail_metadata_alloc_bits;
 
         if ((all_avail & BTRFS_BLOCK_GROUP_RAID10) &&
-            root->fs_info->fs_devices->num_devices <= 4) {
+            btrfs_super_num_devices(&root->fs_info->super_copy) <= 4) {
                 printk("btrfs: unable to go below four devices on raid10\n");
                 ret = -EINVAL;
                 goto out;
         }
 
         if ((all_avail & BTRFS_BLOCK_GROUP_RAID1) &&
-            root->fs_info->fs_devices->num_devices <= 2) {
+            btrfs_super_num_devices(&root->fs_info->super_copy) <= 2) {
                 printk("btrfs: unable to go below two devices on raid1\n");
                 ret = -EINVAL;
                 goto out;
         }
 
-        bdev = open_bdev_excl(device_path, 0, root->fs_info->bdev_holder);
-        if (IS_ERR(bdev)) {
-                ret = PTR_ERR(bdev);
-                goto out;
-        }
+        if (strcmp(device_path, "missing") == 0) {
+                struct list_head *cur;
+                struct list_head *devices;
+                struct btrfs_device *tmp;
 
-        bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
-        if (!bh) {
-                ret = -EIO;
-                goto error_close;
-        }
-        disk_super = (struct btrfs_super_block *)bh->b_data;
-        if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
-            sizeof(disk_super->magic))) {
-                ret = -ENOENT;
-                goto error_brelse;
-        }
-        if (memcmp(disk_super->fsid, root->fs_info->fsid, BTRFS_FSID_SIZE)) {
-                ret = -ENOENT;
-                goto error_brelse;
-        }
-        devid = le64_to_cpu(disk_super->dev_item.devid);
-        device = btrfs_find_device(root, devid, NULL);
-        if (!device) {
-                ret = -ENOENT;
-                goto error_brelse;
-        }
+                device = NULL;
+                devices = &root->fs_info->fs_devices->devices;
+                list_for_each(cur, devices) {
+                        tmp = list_entry(cur, struct btrfs_device, dev_list);
+                        if (tmp->in_fs_metadata && !tmp->bdev) {
+                                device = tmp;
+                                break;
+                        }
+                }
+                bdev = NULL;
+                bh = NULL;
+                disk_super = NULL;
+                if (!device) {
+                        printk("btrfs: no missing devices found to remove\n");
+                        goto out;
+                }
+
+        } else {
+                bdev = open_bdev_excl(device_path, 0,
+                                      root->fs_info->bdev_holder);
+                if (IS_ERR(bdev)) {
+                        ret = PTR_ERR(bdev);
+                        goto out;
+                }
+
+                bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
+                if (!bh) {
+                        ret = -EIO;
+                        goto error_close;
+                }
+                disk_super = (struct btrfs_super_block *)bh->b_data;
+                if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
+                    sizeof(disk_super->magic))) {
+                        ret = -ENOENT;
+                        goto error_brelse;
+                }
+                if (memcmp(disk_super->fsid, root->fs_info->fsid,
+                           BTRFS_FSID_SIZE)) {
+                        ret = -ENOENT;
+                        goto error_brelse;
+                }
+                devid = le64_to_cpu(disk_super->dev_item.devid);
+                device = btrfs_find_device(root, devid, NULL);
+                if (!device) {
+                        ret = -ENOENT;
+                        goto error_brelse;
+                }
 
+        }
         root->fs_info->fs_devices->num_devices--;
 
         ret = btrfs_shrink_device(device, 0);
@@ -764,19 +814,25 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
         if (ret)
                 goto error_brelse;
 
-        /* make sure this device isn't detected as part of the FS anymore */
-        memset(&disk_super->magic, 0, sizeof(disk_super->magic));
-        set_buffer_dirty(bh);
-        sync_dirty_buffer(bh);
-
-        brelse(bh);
-
-        /* one close for the device struct or super_block */
-        close_bdev_excl(device->bdev);
+        if (bh) {
+                /* make sure this device isn't detected as part of
+                 * the FS anymore
+                 */
+                memset(&disk_super->magic, 0, sizeof(disk_super->magic));
+                set_buffer_dirty(bh);
+                sync_dirty_buffer(bh);
 
-        /* one close for us */
-        close_bdev_excl(device->bdev);
+                brelse(bh);
+        }
 
+        if (device->bdev) {
+                /* one close for the device struct or super_block */
+                close_bdev_excl(device->bdev);
+        }
+        if (bdev) {
+                /* one close for us */
+                close_bdev_excl(bdev);
+        }
         kfree(device->name);
         kfree(device);
         ret = 0;
@@ -785,7 +841,8 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 error_brelse:
         brelse(bh);
 error_close:
-        close_bdev_excl(bdev);
+        if (bdev)
+                close_bdev_excl(bdev);
 out:
         mutex_unlock(&uuid_mutex);
         mutex_unlock(&root->fs_info->fs_mutex);
@@ -839,6 +896,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
         device->total_bytes = i_size_read(bdev->bd_inode);
         device->dev_root = root->fs_info->dev_root;
         device->bdev = bdev;
+        device->in_fs_metadata = 1;
 
         ret = btrfs_add_device(trans, root, device);
         if (ret)
@@ -1041,8 +1099,10 @@ int btrfs_relocate_chunk(struct btrfs_root *root,
                                             map->stripes[i].physical);
                 BUG_ON(ret);
 
-                ret = btrfs_update_device(trans, map->stripes[i].dev);
-                BUG_ON(ret);
+                if (map->stripes[i].dev) {
+                        ret = btrfs_update_device(trans, map->stripes[i].dev);
+                        BUG_ON(ret);
+                }
         }
         ret = btrfs_free_chunk(trans, root, chunk_tree, chunk_objectid,
                                chunk_offset);
@@ -1415,10 +1475,13 @@ again:
         while(index < num_stripes) {
                 device = list_entry(cur, struct btrfs_device, dev_alloc_list);
 
-                avail = device->total_bytes - device->bytes_used;
+                if (device->total_bytes > device->bytes_used)
+                        avail = device->total_bytes - device->bytes_used;
+                else
+                        avail = 0;
                 cur = cur->next;
 
-                if (avail >= min_free) {
+                if (device->in_fs_metadata && avail >= min_free) {
                         u64 ignored_start = 0;
                         ret = find_free_dev_extent(trans, device, path,
                                                    min_free,
@@ -1430,7 +1493,7 @@ again:
                                 if (type & BTRFS_BLOCK_GROUP_DUP)
                                         index++;
                         }
-                } else if (avail > max_avail)
+                } else if (device->in_fs_metadata && avail > max_avail)
                         max_avail = avail;
                 if (cur == dev_list)
                         break;
@@ -1610,6 +1673,22 @@ int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
         return ret;
 }
 
+static int find_live_mirror(struct map_lookup *map, int first, int num,
+                            int optimal)
+{
+        int i;
+        if (map->stripes[optimal].dev->bdev)
+                return optimal;
+        for (i = first; i < first + num; i++) {
+                if (map->stripes[i].dev->bdev)
+                        return i;
+        }
+        /* we couldn't find one that doesn't fail.  Just return something
+         * and the io error handling code will clean up eventually
+         */
+        return optimal;
+}
+
 static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                              u64 logical, u64 *length,
                              struct btrfs_multi_bio **multi_ret,
@@ -1712,8 +1791,11 @@ again:
                         num_stripes = map->num_stripes;
                 else if (mirror_num)
                         stripe_index = mirror_num - 1;
-                else
-                        stripe_index = current->pid % map->num_stripes;
+                else {
+                        stripe_index = find_live_mirror(map, 0,
+                                            map->num_stripes,
+                                            current->pid % map->num_stripes);
+                }
 
         } else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
                 if (rw & (1 << BIO_RW))
@@ -1731,8 +1813,11 @@ again:
                         num_stripes = map->sub_stripes;
                 else if (mirror_num)
                         stripe_index += mirror_num - 1;
-                else
-                        stripe_index += current->pid % map->sub_stripes;
+                else {
+                        stripe_index = find_live_mirror(map, stripe_index,
+                                              map->sub_stripes, stripe_index +
+                                              current->pid % map->sub_stripes);
+                }
         } else {
                 /*
                  * after this do_div call, stripe_nr is the number of stripes
@@ -1749,9 +1834,11 @@ again:
                         struct backing_dev_info *bdi;
 
                         device = map->stripes[stripe_index].dev;
-                        bdi = blk_get_backing_dev_info(device->bdev);
-                        if (bdi->unplug_io_fn) {
-                                bdi->unplug_io_fn(bdi, unplug_page);
+                        if (device->bdev) {
+                                bdi = blk_get_backing_dev_info(device->bdev);
+                                if (bdi->unplug_io_fn) {
+                                        bdi->unplug_io_fn(bdi, unplug_page);
+                                }
                         }
                 } else {
                         multi->stripes[i].physical =
@@ -1880,12 +1967,21 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
                 }
                 bio->bi_sector = multi->stripes[dev_nr].physical >> 9;
                 dev = multi->stripes[dev_nr].dev;
-
-                bio->bi_bdev = dev->bdev;
-                spin_lock(&dev->io_lock);
-                dev->total_ios++;
-                spin_unlock(&dev->io_lock);
-                submit_bio(rw, bio);
+                if (dev && dev->bdev) {
+                        bio->bi_bdev = dev->bdev;
+                        spin_lock(&dev->io_lock);
+                        dev->total_ios++;
+                        spin_unlock(&dev->io_lock);
+                        submit_bio(rw, bio);
+                } else {
+                        bio->bi_bdev = root->fs_info->fs_devices->latest_bdev;
+                        bio->bi_sector = logical >> 9;
+#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
+                        bio_endio(bio, bio->bi_size, -EIO);
+#else
+                        bio_endio(bio, -EIO);
+#endif
+                }
                 dev_nr++;
         }
         if (total_devs == 1)
@@ -1901,6 +1997,27 @@ struct btrfs_device *btrfs_find_device(struct btrfs_root *root, u64 devid,
         return __find_device(head, devid, uuid);
 }
 
+static struct btrfs_device *add_missing_dev(struct btrfs_root *root,
+                                            u64 devid, u8 *dev_uuid)
+{
+        struct btrfs_device *device;
+        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
+
+        device = kzalloc(sizeof(*device), GFP_NOFS);
+        list_add(&device->dev_list,
+                 &fs_devices->devices);
+        list_add(&device->dev_alloc_list,
+                 &fs_devices->alloc_list);
+        device->barriers = 1;
+        device->dev_root = root->fs_info->dev_root;
+        device->devid = devid;
+        fs_devices->num_devices++;
+        spin_lock_init(&device->io_lock);
+        memcpy(device->uuid, dev_uuid, BTRFS_UUID_SIZE);
+        return device;
+}
+
+
 static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
                           struct extent_buffer *leaf,
                           struct btrfs_chunk *chunk)
@@ -1965,11 +2082,22 @@ static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
                                    btrfs_stripe_dev_uuid_nr(chunk, i),
                                    BTRFS_UUID_SIZE);
                 map->stripes[i].dev = btrfs_find_device(root, devid, uuid);
-                if (!map->stripes[i].dev) {
+
+                if (!map->stripes[i].dev && !btrfs_test_opt(root, DEGRADED)) {
                         kfree(map);
                         free_extent_map(em);
                         return -EIO;
                 }
+                if (!map->stripes[i].dev) {
+                        map->stripes[i].dev =
+                                add_missing_dev(root, devid, uuid);
+                        if (!map->stripes[i].dev) {
+                                kfree(map);
+                                free_extent_map(em);
+                                return -EIO;
+                        }
+                }
+                map->stripes[i].dev->in_fs_metadata = 1;
         }
 
         spin_lock(&map_tree->map_tree.lock);
@@ -2016,20 +2144,15 @@ static int read_one_dev(struct btrfs_root *root,
                            BTRFS_UUID_SIZE);
         device = btrfs_find_device(root, devid, dev_uuid);
         if (!device) {
-                printk("warning devid %Lu not found already\n", devid);
-                device = kzalloc(sizeof(*device), GFP_NOFS);
+                printk("warning devid %Lu missing\n", devid);
+                device = add_missing_dev(root, devid, dev_uuid);
                 if (!device)
                         return -ENOMEM;
-                list_add(&device->dev_list,
-                         &root->fs_info->fs_devices->devices);
-                list_add(&device->dev_alloc_list,
-                         &root->fs_info->fs_devices->alloc_list);
-                device->barriers = 1;
-                spin_lock_init(&device->io_lock);
         }
 
         fill_device_from_item(leaf, dev_item, device);
         device->dev_root = root->fs_info->dev_root;
+        device->in_fs_metadata = 1;
         ret = 0;
 #if 0
         ret = btrfs_open_device(device);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 0f94a69e6eb6..454fe8103329 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -27,8 +27,10 @@ struct btrfs_device {
         struct list_head dev_alloc_list;
         struct btrfs_root *dev_root;
         struct buffer_head *pending_io;
+        u64 generation;
 
         int barriers;
+        int in_fs_metadata;
 
         spinlock_t io_lock;
 
@@ -122,6 +124,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 int btrfs_scan_one_device(const char *path, int flags, void *holder,
                           struct btrfs_fs_devices **fs_devices_ret);
 int btrfs_close_devices(struct btrfs_fs_devices *fs_devices);
+int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices);
 int btrfs_add_device(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_device *device);