4 files changed, 284 insertions, 0 deletions
diff --git a/pkg/sentry/context/BUILD b/pkg/sentry/context/BUILD
new file mode 100644
index 000000000..ff39f94ba
--- /dev/null
+++ b/pkg/sentry/context/BUILD
@@ -0,0 +1,14 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "context",
+    srcs = ["context.go"],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/context",
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/amutex",
+        "//pkg/log",
+    ],
+)
diff --git a/pkg/sentry/context/context.go b/pkg/sentry/context/context.go
new file mode 100644
index 000000000..e0dffafba
--- /dev/null
+++ b/pkg/sentry/context/context.go
@@ -0,0 +1,103 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package context defines the sentry's Context type.
+package context
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/amutex"
+	"gvisor.googlesource.com/gvisor/pkg/log"
+)
+
+// A Context represents a thread of execution (hereafter "goroutine" to reflect
+// Go idiosyncrasy). It carries state associated with the goroutine across API
+// boundaries.
+//
+// While Context exists for essentially the same reasons as Go's standard
+// context.Context, the standard type represents the state of an operation
+// rather than that of a goroutine. This is a critical distinction:
+//
+// - Unlike context.Context, which "may be passed to functions running in
+// different goroutines", it is *not safe* to use the same Context in multiple
+// concurrent goroutines.
+//
+// - It is *not safe* to retain a Context passed to a function beyond the scope
+// of that function call.
+//
+// In both cases, values extracted from the Context should be used instead.
+type Context interface {
+	log.Logger
+	amutex.Sleeper
+
+	// UninterruptibleSleepStart indicates the beginning of an uninterruptible
+	// sleep state (equivalent to Linux's TASK_UNINTERRUPTIBLE). If deactivate
+	// is true and the Context represents a Task, the Task's AddressSpace is
+	// deactivated.
+	UninterruptibleSleepStart(deactivate bool)
+
+	// UninterruptibleSleepFinish indicates the end of an uninterruptible sleep
+	// state that was begun by a previous call to UninterruptibleSleepStart. If
+	// activate is true and the Context represents a Task, the Task's
+	// AddressSpace is activated. Normally activate is the same value as the
+	// deactivate parameter passed to UninterruptibleSleepStart.
+	UninterruptibleSleepFinish(activate bool)
+
+	// Value returns the value associated with this Context for key, or nil if
+	// no value is associated with key. Successive calls to Value with the same
+	// key returns the same result.
+	//
+	// A key identifies a specific value in a Context. Functions that wish to
+	// retrieve values from Context typically allocate a key in a global
+	// variable then use that key as the argument to Context.Value. A key can
+	// be any type that supports equality; packages should define keys as an
+	// unexported type to avoid collisions.
+	Value(key interface{}) interface{}
+}
+
+type logContext struct {
+	log.Logger
+	NoopSleeper
+}
+
+// Value implements Context.Value.
+func (logContext) Value(key interface{}) interface{} {
+	return nil
+}
+
+// NoopSleeper is a noop implementation of amutex.Sleeper and
+// Context.UninterruptibleSleep* methods for anonymous embedding in other types
+// that do not want to notify kernel.Task about sleeps.
+type NoopSleeper struct {
+	amutex.NoopSleeper
+}
+
+// UninterruptibleSleepStart does nothing.
+func (NoopSleeper) UninterruptibleSleepStart(bool) {}
+
+// UninterruptibleSleepFinish does nothing.
+func (NoopSleeper) UninterruptibleSleepFinish(bool) {}
+
+// Background returns an empty context using the default logger.
+//
+// Users should be wary of using a Background context. Please tag any use with
+// FIXME and a note to remove this use.
+//
+// Generally, one should use the Task as their context when available, or avoid
+// having to use a context in places where a Task is unavailable.
+//
+// Using a Background context for tests is fine, as long as no values are
+// needed from the context in the tested code paths.
+func Background() Context {
+	return logContext{Logger: log.Log()}
+}
diff --git a/pkg/sentry/context/contexttest/BUILD b/pkg/sentry/context/contexttest/BUILD
new file mode 100644
index 000000000..5977344de
--- /dev/null
+++ b/pkg/sentry/context/contexttest/BUILD
@@ -0,0 +1,34 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("//tools/go_stateify:defs.bzl", "go_stateify")
+
+go_stateify(
+    name = "contexttest_state",
+    srcs = [
+        "contexttest.go",
+    ],
+    out = "contexttest_state.go",
+    package = "contexttest",
+)
+
+go_library(
+    name = "contexttest",
+    testonly = 1,
+    srcs = [
+        "contexttest.go",
+        "contexttest_state.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest",
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/sentry/context",
+        "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/time",
+        "//pkg/sentry/limits",
+        "//pkg/sentry/platform",
+        "//pkg/sentry/platform/ptrace",
+        "//pkg/sentry/uniqueid",
+        "//pkg/state",
+    ],
+)
diff --git a/pkg/sentry/context/contexttest/contexttest.go b/pkg/sentry/context/contexttest/contexttest.go
new file mode 100644
index 000000000..193ce3440
--- /dev/null
+++ b/pkg/sentry/context/contexttest/contexttest.go
@@ -0,0 +1,133 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package contexttest builds a test context.Context.
+package contexttest
+
+import (
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
+	ktime "gvisor.googlesource.com/gvisor/pkg/sentry/kernel/time"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/limits"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform/ptrace"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/uniqueid"
+)
+
+// Context returns a Context that may be used in tests. Uses ptrace as the
+// platform.Platform.
+func Context(tb testing.TB) context.Context {
+	p, err := ptrace.New()
+	if err != nil {
+		tb.Fatal(err)
+	}
+	// Test usage of context.Background is fine.
+	return &testContext{
+		Context:  context.Background(),
+		l:        limits.NewLimitSet(),
+		platform: p,
+	}
+}
+
+type testContext struct {
+	context.Context
+	l        *limits.LimitSet
+	platform platform.Platform
+}
+
+// globalUniqueID tracks incremental unique identifiers for tests.
+var globalUniqueID uint64
+
+// lastInotifyCookie is a monotonically increasing counter for generating unique
+// inotify cookies. Must be accessed using atomic ops.
+var lastInotifyCookie uint32
+
+// hostClock implements ktime.Clock.
+type hostClock struct {
+	ktime.WallRateClock
+	ktime.NoClockEvents
+}
+
+// Now implements ktime.Clock.Now.
+func (hostClock) Now() ktime.Time {
+	return ktime.FromNanoseconds(time.Now().UnixNano())
+}
+
+// Value implements context.Context.
+func (t *testContext) Value(key interface{}) interface{} {
+	switch key {
+	case limits.CtxLimits:
+		return t.l
+	case platform.CtxPlatform:
+		return t.platform
+	case uniqueid.CtxGlobalUniqueID:
+		return atomic.AddUint64(&globalUniqueID, 1)
+	case uniqueid.CtxInotifyCookie:
+		return atomic.AddUint32(&lastInotifyCookie, 1)
+	case ktime.CtxRealtimeClock:
+		return hostClock{}
+	default:
+		return t.Context.Value(key)
+	}
+}
+
+// RootContext returns a Context that may be used in tests that need root
+// credentials. Uses ptrace as the platform.Platform.
+func RootContext(tb testing.TB) context.Context {
+	return WithCreds(Context(tb), auth.NewRootCredentials(auth.NewRootUserNamespace()))
+}
+
+// WithCreds returns a copy of ctx carrying creds.
+func WithCreds(ctx context.Context, creds *auth.Credentials) context.Context {
+	return &authContext{ctx, creds}
+}
+
+type authContext struct {
+	context.Context
+	creds *auth.Credentials
+}
+
+// Value implements context.Context.
+func (ac *authContext) Value(key interface{}) interface{} {
+	switch key {
+	case auth.CtxCredentials:
+		return ac.creds
+	default:
+		return ac.Context.Value(key)
+	}
+}
+
+// WithLimitSet returns a copy of ctx carrying l.
+func WithLimitSet(ctx context.Context, l *limits.LimitSet) context.Context {
+	return limitContext{ctx, l}
+}
+
+type limitContext struct {
+	context.Context
+	l *limits.LimitSet
+}
+
+// Value implements context.Context.
+func (lc limitContext) Value(key interface{}) interface{} {
+	switch key {
+	case limits.CtxLimits:
+		return lc.l
+	default:
+		return lc.Context.Value(key)
+	}
+}