# btrd
The btrfs debugger (pronounced "buttered").
`btrd` is a [REPL][0] debugger that helps inspect mounted btrfs filesystems.
btrd is particularly useful in exploring on-disk structures and has full
knowledge of all on-disk types.
### Demo
```
$ sudo btrd
btrd (the btrfs debugger) v0.1.0
Type 'help' for help
(btrd) filesystem "/mnt/btrfs"
(btrd) k = key(BTRFS_DEV_TREE_OBJECTID, BTRFS_ROOT_ITEM_KEY, 0, 0)
(btrd) print k
struct _btrfs_ioctl_search_key {
.min_objectid = 4,
.max_objectid = 18446744073709551615,
.min_type = 132,
.max_type = 255,
.min_offset = 0,
.max_offset = 18446744073709551615,
.min_transid = 0,
.max_transid = 18446744073709551615,
}
(btrd) res = search(BTRFS_ROOT_TREE_OBJECTID, k)
(btrd) len(res)
297
(btrd) res[0]
struct btrfs_root_item {
.inode = struct btrfs_inode_item {
.generation = 1,
.transid = 0,
.size = 3,
.nbytes = 16384,
<...>
.sequence = 0,
.reserved = [
0,
0,
0,
0,
],
.atime = struct btrfs_timespec {
.sec = 0,
.nsec = 0,
},
<...>
(btrd) print res[0].inode.nbytes
16384
(btrd) typeof(res[0])
"struct btrfs_root_item"
(btrd) keyof(res[0])
struct btrfs_key {
.objectid = 4,
.type = 132,
.offset = 0,
}
```
### Building
```bash
$ git clone https://github.com/danobi/btrd.git
$ cd btrd
$ cargo build --release
$ sudo ./target/release/btrd
```
### Language features
btrd's scripting language is not a hack -- it's a dynamically typed language
tailored to filesystem debugging. The following is a list of language features:
Types:
* Strings
* Integers (all integers are internally represented as i128)
* Booleans
* Arrays (may not be user instantiated)
* Structs (may not be user defined/instantiated)
* Functions (first-class support; may not be user defined)
Expressions:
* Binary expressions (`+`, `-`, `/`, `%`, `>>`, `&&`, `==`, etc.)
* Unary expressions (`-`, `~`, `!`)
* Parentheses
* Function calls
* Struct field access
* Array indexes
* Type casts (`(struct btrfs_root) physical_bytenr`)
Control flow:
* `while`
* `for` (ranged based)
* `if/else`
There is not and **will not** be support for:
* Floating point
[0]: https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop