Inspect validator puppet architecture
Overview
The Validator program sends FIDL commands to control a “puppet” program, which invokes library functionality to modify some state that the Validator then evaluates. For more information about the Inspect Validator, see the README.
The Puppet includes these parts:
- Serving a FIDL protocol.
- Unpacking the protocol and making library calls.
- Building an integration test that includes the Puppet and Validator programs.
This doc focuses on the Inspect Validator Rust Puppet located at //src/diagnostics/validator/inspect/lib/rust/src/main.rs.
FIDL design
The FIDL protocol for Inspect Validator is defined in //src/diagnostics/validator/inspect/fidl/validate.test.fidl. The FIDL protocol corresponds closely to the functions in the Inspect library API which defines actions to be applied to any Inspect API implementation. The FIDL API is written to correspond to the Rust API.
(Note: Inspect APIs are allowed to differ from the Rust API; such APIs may require puppet code architecture modifications.)
Serving FIDL
The main()
function performs boilerplate to serve a single FIDL client
through run_driver_service()
, which receives either Initialize
or Act
events from the FIDL stream. Act
events are unpacked by the Actor
object
which maintains the state necessary to control the Inspect library.
Actor and the Inspect library
Actor
contains an Inspector
(the Inspect library’s entry-point object),
a hashmap of nodes
, and a hashmap of properties
. It implements one
function, act()
, which contains a giant match
statement (“switch” or “case”
in other languages) to invoke each action that the library implements.
Puppets can report Unimplemented
for actions the library doesn’t support.
After the Validator invokes each action, it will test the library’s effect on the VMO. The library should handle propagating the effects of actions so that the Validator can see them.
The hashmaps of nodes
and properties
store values that are returned by the
Inspect library. Since Rust is an RAII language that cleans up automatically
when reference to memory is lost, failing to store a node or property would
cause immediate deletion of that node or property. Also, storing properties
allows updating their values in response to FIDL commands.
Testing and the build system
The Validator and Puppet combination should make a hermetic integration test.
Note: due to limitations in the Dart build-system macros, the Dart test isn’t fully hermetic.
Dependencies and names
Validator’s BUILD.gn file
defines a validator_bin
target, which is used by the
Rust puppet’s BUILD.gn file
as a dependency to the test_package()
named inspect_validator_test_rust
which is the test that exercises the Rust puppet.
The Rust puppet itself is
built as a standard rustc_binary.
That build rule produces two names, inspect_validator_rust_puppet_bin
, which
is included in the deps of the test_package()
rule, and
inspect_validator_rust_puppet
, which is included in the binaries of the
test_package()
.
The validator_bin
target from the
Validator’s Build.gn file
has a name of validator
, which is referred to in the tests
of the
test_package()
.
CQ/CI
Putting inspect_validator_test_rust
in the deps
of group("tests")
in its
BUILD.gn
makes it easy to include inspect_validator/lib/rust:tests
in the deps
of
group("tests")
of src/diagnostics/BUILD.gn.
This will be picked up by the build system and cause the Inspect Validator Rust
Puppet test to be run in CQ and CI.
Meta .cmx files
There are the following CMX files in //src/diagnostics/validator/inspect/lib/rust/meta:
inspect-validator-rust-puppet.cmx
Lets the puppet binary run and use the logger. It’s referred to in the
meta
section oftest_package("inspect_validator_test_rust")
.-
This CMX file is implicitly referred to by the
tests: name: "validator"
that you specified intest_package()
.sandbox: services
specifies the services that the Validator needs to run.program: args
supplies command-line arguments to the Validator, including the complete URL of the Rust puppet.program: binary
confirms that you want to run thetests: name: "validator"
.
Running Validator
For information on how to run the Validator against a puppet, see Inspect Validator.