This document explains how to read the bitfield diagrams used in the logs and inspect formats.
The following example bitfield diagram is broken down into its component parts:
.---------------------------------------------------------------.
| |1|1|1|1|1|2|2|2|2|2|3|3|3|3|3|4|4|4|4|4|5|5|5|5|5|6|6|
|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|
|---+---+-------+-----------------------+-----------------------|
| O | R | Type | Parent index | Name index |
|---------------------------------------------------------------|
| Reference count (optional) |
'---------------------------------------------------------------'
O = Order
R = Reserved, must be 0
Type = {3,10}
In the top row, each column denotes the starting bit index, and each space corresponds to two consecutive bits.
For example, the first “0” in the left-most column denotes that the space is reserved for the bits at index 0 and 1. The next “2” at index 2 and 3, and so on. The first column with two numbers should be read as “10”, the next “12”, and so on.
.---------------------------------------------------------------. | |1|1|1|1|1|2|2|2|2|2|3|3|3|3|3|4|4|4|4|4|5|5|5|5|5|6|6| |0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2|4|6|8|0|2| |---+-----------+-----------------------------------------------|
The bottom rows of the diagram illustrate the physical layout of the fields. Each row consists of 64 bits.
|---+---+-------+-----------------------+-----------------------| | O | R | Type | Parent index | Name index | |---------------------------------------------------------------| | Reference count (optional) | '---------------------------------------------------------------'
In the example, we are representing 128 bits. The first 64 bits contain:
O: 4 bits at indexes [0, 4) (left inclusive, right exclusive, so in this case the indexes {0, 1, 2, 3}).R: 4 bits at indexes [4, 8)Type: 8 bits at indexes [8, 16)Parent index: 24 bits at indexes [16, 40)Name index: 24 bits at indexes [40, 64)The second 64 bits contain a single value, the Reference count.
At the end of the diagram, there is a legend to make it clearer what some fields mean or what restrictions they might have. In the example above, R means Reserved and O means Order but there wasn’t enough space in the diagram to fit those words. Type will only contain values in the set {3, 10}.