feat: implement agent process management (#9461)

- An opt-in feature has been added to the agent to allow
   deprioritizing non coder-related processes for CPU by setting their
   niceness level to 10.
- Opting in to the feature requires setting CODER_PROC_PRIO_MGMT to a non-empty value.

agent/agentproc/agentproctest/doc.go

@@ -0,0 +1,5 @@
+// Package agentproctest contains utility functions
+// for testing process management in the agent.
+package agentproctest
+
+//go:generate mockgen -destination ./syscallermock.go -package agentproctest github.com/coder/coder/v2/agent/agentproc Syscaller

agent/agentproc/agentproctest/proc.go

@@ -0,0 +1,49 @@
+package agentproctest
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/agent/agentproc"
+	"github.com/coder/coder/v2/cryptorand"
+)
+
+func GenerateProcess(t *testing.T, fs afero.Fs, muts ...func(*agentproc.Process)) agentproc.Process {
+	t.Helper()
+
+	pid, err := cryptorand.Intn(1<<31 - 1)
+	require.NoError(t, err)
+
+	arg1, err := cryptorand.String(5)
+	require.NoError(t, err)
+
+	arg2, err := cryptorand.String(5)
+	require.NoError(t, err)
+
+	arg3, err := cryptorand.String(5)
+	require.NoError(t, err)
+
+	cmdline := fmt.Sprintf("%s\x00%s\x00%s", arg1, arg2, arg3)
+
+	process := agentproc.Process{
+		CmdLine: cmdline,
+		PID:     int32(pid),
+	}
+
+	for _, mut := range muts {
+		mut(&process)
+	}
+
+	process.Dir = fmt.Sprintf("%s/%d", "/proc", process.PID)
+
+	err = fs.MkdirAll(process.Dir, 0o555)
+	require.NoError(t, err)
+
+	err = afero.WriteFile(fs, fmt.Sprintf("%s/cmdline", process.Dir), []byte(process.CmdLine), 0o444)
+	require.NoError(t, err)
+
+	return process
+}

agent/agentproc/agentproctest/syscallermock.go

@@ -0,0 +1,78 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/coder/coder/v2/agent/agentproc (interfaces: Syscaller)
+
+// Package agentproctest is a generated GoMock package.
+package agentproctest
+
+import (
+	reflect "reflect"
+	syscall "syscall"
+
+	gomock "github.com/golang/mock/gomock"
+)
+
+// MockSyscaller is a mock of Syscaller interface.
+type MockSyscaller struct {
+	ctrl     *gomock.Controller
+	recorder *MockSyscallerMockRecorder
+}
+
+// MockSyscallerMockRecorder is the mock recorder for MockSyscaller.
+type MockSyscallerMockRecorder struct {
+	mock *MockSyscaller
+}
+
+// NewMockSyscaller creates a new mock instance.
+func NewMockSyscaller(ctrl *gomock.Controller) *MockSyscaller {
+	mock := &MockSyscaller{ctrl: ctrl}
+	mock.recorder = &MockSyscallerMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockSyscaller) EXPECT() *MockSyscallerMockRecorder {
+	return m.recorder
+}
+
+// GetPriority mocks base method.
+func (m *MockSyscaller) GetPriority(arg0 int32) (int, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "GetPriority", arg0)
+	ret0, _ := ret[0].(int)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// GetPriority indicates an expected call of GetPriority.
+func (mr *MockSyscallerMockRecorder) GetPriority(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetPriority", reflect.TypeOf((*MockSyscaller)(nil).GetPriority), arg0)
+}
+
+// Kill mocks base method.
+func (m *MockSyscaller) Kill(arg0 int32, arg1 syscall.Signal) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Kill", arg0, arg1)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// Kill indicates an expected call of Kill.
+func (mr *MockSyscallerMockRecorder) Kill(arg0, arg1 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Kill", reflect.TypeOf((*MockSyscaller)(nil).Kill), arg0, arg1)
+}
+
+// SetPriority mocks base method.
+func (m *MockSyscaller) SetPriority(arg0 int32, arg1 int) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "SetPriority", arg0, arg1)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// SetPriority indicates an expected call of SetPriority.
+func (mr *MockSyscallerMockRecorder) SetPriority(arg0, arg1 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "SetPriority", reflect.TypeOf((*MockSyscaller)(nil).SetPriority), arg0, arg1)
+}