Attribute - $INDEX_ROOT (0x90)
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Overview
This is the root node of the B+ tree that implements an index (e.g. a directory).
This file attribute is always resident.
Always resident.
Layout of the Attribute
link up below
- $INDEX_ROOT
- Standard Attribute Header
- Index Root
- Index Header
- Index Entry
- Index Entry
- ...
Index Root
Offset |
Size |
Description |
~ |
~ |
Standard Attribute Header |
0x00 |
4 |
Attribute Type |
0x04 |
4 |
Collation Rule |
0x08 |
4 |
Size of Index Allocation Entry (bytes) |
0x0C |
1 |
Clusters per Index Record |
0x0D |
3 |
Padding (Align to 8 bytes) |
Index Header
Offset |
Size |
Description |
0x00 |
4 |
Offset to first Index Entry |
0x04 |
4 |
Total size of the Index Entries |
0x08 |
4 |
Allocated size of the Index Entries |
0x0C |
1 |
Flags |
0x0D |
3 |
Padding (align to 8 bytes) |
Notes
Size
As defined in $AttrDef, this attribute
has a no minimum or maximum size.
Flags
Flag |
Description |
0x00 |
Small Index (fits in Index Root) |
0x01 |
Large index (Index Allocation needed) |
silly to have a flag of 0x00, remove
The large index flag indicates whether the file attributes index allocation
and bitmap are present (when the index is small enough to be stored completely in
the root node, these two file attributes are missing).
Sequence of index entries
This is a sequence of index entries that has a variable length. The sequence is
terminated with a special index entry whose last entry flag is set.
This is the header for indexes, describing the INDEX_ENTRY records, which
follow the INDEX_HEADER. Together the index header and the index entries
make up a complete index.
This is followed by a sequence of index entries (INDEX_ENTRY structures)
as described by the index header.
When a directory is small enough to fit inside the index root then this
is the only attribute describing the directory. When the directory is too
large to fit in the index root, on the other hand, two aditional attributes
are present: an index allocation attribute, containing sub-nodes of the B+
directory tree (see below), and a bitmap attribute, describing which virtual
cluster numbers (vcns) in the index allocation attribute are in use by an
index block.
NOTE: The root directory (FILE_$root) contains an entry for itself.
struct {
ATTR_TYPES type;
Type of the indexed attribute. Is $FILENAME for directories, zero
for view indexes. No other values allowed.
COLLATION_RULES collation_rule; Collation rule used to sort the
index entries. If type is $FILENAME, this must be COLLATION_FILENAME.
__u32 bytes_per_index_block;
Byte size of each index block (in the index allocation attribute).
__u8 clusters_per_index_block;
Cluster size of each index block (in the index allocation attribute), when
an index block is >= than a cluster, otherwise this will be the log of
the size (like how the encoding of the mft record size and the index
record size found in the boot sector work). Has to be a power of 2.
} INDEX_ROOT;
List of Common Indexes
which elements are shared between indexes?
not relevant for index root
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