Fill missing devices so degraded filesystems can be read

When a device is missing, the btrfs tools need to be able to read alternate
copies from the remaining devices.  This creates placeholder devices
that always return -EIO so the tools can limp along.

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

2 files changed, 14 insertions, 2 deletions

diff --git a/disk-io.c b/disk-io.c
index a6e1000d..fef3edab 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -204,6 +204,7 @@ struct extent_buffer *read_tree_block(struct btrfs_root *root, u64 bytenr,
 		eb->dev_bytenr = multi->stripes[0].physical;
 		kfree(multi);
 		ret = read_extent_from_disk(eb);
+
 		if (ret == 0 && check_tree_block(root, eb) == 0 &&
 		    csum_tree_block(root, eb, 1) == 0 &&
 		    verify_parent_transid(eb->tree, eb, parent_transid) == 0) {
diff --git a/volumes.c b/volumes.c
index 76718550..b8f71673 100644
--- a/volumes.c
+++ b/volumes.c
@@ -1159,6 +1159,16 @@ int btrfs_chunk_readonly(struct btrfs_root *root, u64 chunk_offset)
 	return readonly;
 }
 
+static struct btrfs_device *fill_missing_device(u64 devid)
+{
+	struct btrfs_device *device;
+
+	device = kzalloc(sizeof(*device), GFP_NOFS);
+	device->devid = devid;
+	device->fd = -1;
+	return device;
+}
+
 static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
 			  struct extent_buffer *leaf,
 			  struct btrfs_chunk *chunk)
@@ -1209,8 +1219,9 @@ static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
 		map->stripes[i].dev = btrfs_find_device(root, devid, uuid,
 							NULL);
 		if (!map->stripes[i].dev) {
-			kfree(map);
-			return -EIO;
+			map->stripes[i].dev = fill_missing_device(devid);
+			printf("warning, device %llu is missing\n",
+			       (unsigned long long)devid);
 		}
 
 	}