Show Dev Extents

The DEV TREE shows a mapping from all allocated blocks on the physical
storage back to chunks and their stripes.

    >>> import btrfs
    >>> from __future__ import print_function
    >>> fs=btrfs.FileSystem('/mnt/extents')
    >>> map(print, fs.dev_extents())
    dev extent devid 1 paddr 1048576 length 134217728 chunk 14348713984
    dev extent devid 1 paddr 135266304 length 33554432 chunk 14617149440
    dev extent devid 1 paddr 168820736 length 1073741824 chunk 16831741952
    dev extent devid 1 paddr 2436890624 length 1073741824 chunk 12201230336
    dev extent devid 2 paddr 1048576 length 1073741824 chunk 12201230336
    dev extent devid 2 paddr 1074790400 length 134217728 chunk 14348713984
    dev extent devid 2 paddr 1209008128 length 33554432 chunk 14617149440
    dev extent devid 2 paddr 1242562560 length 1073741824 chunk 16831741952

Or, with some information about the chunk they refer to:

    # ./show_dev_extents.py /mnt/extents/
    devid 1 type METADATA|RAID0 pstart 1.00MiB length 128.00MiB pend 129.00MiB vaddr 13.36GiB
    devid 1 type SYSTEM|RAID0 pstart 129.00MiB length 32.00MiB pend 161.00MiB vaddr 13.61GiB
    devid 1 type DATA|RAID0 pstart 161.00MiB length 1.00GiB pend 1.16GiB vaddr 15.68GiB
    devid 1 type DATA|RAID0 pstart 2.27GiB length 1.00GiB pend 3.27GiB vaddr 11.36GiB
    devid 2 type DATA|RAID0 pstart 1.00MiB length 1.00GiB pend 1.00GiB vaddr 11.36GiB
    devid 2 type METADATA|RAID0 pstart 1.00GiB length 128.00MiB pend 1.13GiB vaddr 13.36GiB
    devid 2 type SYSTEM|RAID0 pstart 1.13GiB length 32.00MiB pend 1.16GiB vaddr 13.61GiB
    devid 2 type DATA|RAID0 pstart 1.16GiB length 1.00GiB pend 2.16GiB vaddr 15.68GiB

btrfs/ctree.py

@@ -35,6 +35,7 @@ def ULL(n):
 ROOT_TREE_OBJECTID = 1
 EXTENT_TREE_OBJECTID = 2
 CHUNK_TREE_OBJECTID = 3
+DEV_TREE_OBJECTID = 4
 FIRST_CHUNK_TREE_OBJECTID = 256
 ORPHAN_OBJECTID = ULL(-5)
 
@@ -43,6 +44,7 @@ def ULL(n):
 EXTENT_DATA_REF_KEY = 178
 SHARED_DATA_REF_KEY = 184
 BLOCK_GROUP_ITEM_KEY = 192
+DEV_EXTENT_KEY = 204
 DEV_ITEM_KEY = 216
 CHUNK_ITEM_KEY = 228
 
@@ -103,6 +105,7 @@ def key_objectid_str(objectid, _type):
     EXTENT_DATA_REF_KEY: 'EXTENT_DATA_REF',
     SHARED_DATA_REF_KEY: 'SHARED_DATA_REF',
     BLOCK_GROUP_ITEM_KEY: 'BLOCK_GROUP_ITEM',
+    DEV_EXTENT_KEY: 'DEV_EXTENT',
     DEV_ITEM_KEY: 'DEV_ITEM',
     CHUNK_ITEM_KEY: 'CHUNK_ITEM',
 }
@@ -234,6 +237,12 @@ def chunks(self, min_vaddr=0, max_vaddr=ULLONG_MAX, nr_items=ULONG_MAX):
                                                nr_items=nr_items):
             yield Chunk(header, data)
 
+    def dev_extents(self):
+        tree = DEV_TREE_OBJECTID
+        for header, data in btrfs.ioctl.search(self.fd, tree):
+            if header.type == DEV_EXTENT_KEY:
+                yield DevExtent(header, data)
+
     def block_group(self, vaddr, length=None):
         tree = EXTENT_TREE_OBJECTID
         min_offset = length if length is not None else 0
@@ -324,6 +333,23 @@ def __str__(self):
         return "stripe devid {0} offset {1}".format(self.devid, self.offset)
 
 
+class DevExtent(object):
+    dev_extent = struct.Struct("<4Q16s")
+
+    def __init__(self, header, data):
+        self.key = Key(header.objectid, header.type, header.offset)
+        self.devid = header.objectid
+        self.paddr = header.offset
+        self.chunk_tree, self.chunk_objectid, self.chunk_offset, self.length, uuid_bytes = \
+            DevExtent.dev_extent.unpack_from(data, 0)
+        self.vaddr = self.chunk_offset
+        self.uuid = uuid.UUID(bytes=uuid_bytes)
+
+    def __str__(self):
+        return "dev extent devid {0} paddr {1} length {2} chunk {3}".format(
+            self.devid, self.paddr, self.length, self.chunk_offset)
+
+
 class BlockGroup(object):
     block_group_item = struct.Struct("<3Q")
 

examples/show_dev_extents.py

@@ -0,0 +1,17 @@
+#!/usr/bin/python
+
+from __future__ import print_function
+import btrfs
+import sys
+
+fs = btrfs.FileSystem(sys.argv[1])
+chunks = {chunk.vaddr: chunk for chunk in fs.chunks()}
+for d in fs.dev_extents():
+    print("devid {0} type {1} pstart {2} length {3} pend {4} vaddr {5}".format(
+        d.devid,
+        btrfs.utils.block_group_flags_str(chunks[d.vaddr].type),
+        btrfs.utils.pretty_size(d.paddr),
+        btrfs.utils.pretty_size(d.length),
+        btrfs.utils.pretty_size(d.paddr + d.length),
+        btrfs.utils.pretty_size(d.vaddr)
+    ))