2 files changed, 154 insertions, 0 deletions
diff --git a/pkg/context/BUILD b/pkg/context/BUILD
new file mode 100644
index 000000000..239f31149
--- /dev/null
+++ b/pkg/context/BUILD
@@ -0,0 +1,13 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "context",
+    srcs = ["context.go"],
+    visibility = ["//:sandbox"],
+    deps = [
+        "//pkg/amutex",
+        "//pkg/log",
+    ],
+)
diff --git a/pkg/context/context.go b/pkg/context/context.go
new file mode 100644
index 000000000..23e009ef3
--- /dev/null
+++ b/pkg/context/context.go
@@ -0,0 +1,141 @@
+// Copyright 2018 The gVisor Authors.
+//
+// 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 an internal context type.
+//
+// The given Context conforms to the standard Go context, but mandates
+// additional methods that are specific to the kernel internals. Note however,
+// that the Context described by this package carries additional constraints
+// regarding concurrent access and retaining beyond the scope of a call.
+//
+// See the Context type for complete details.
+package context
+
+import (
+	"context"
+	"time"
+
+	"gvisor.dev/gvisor/pkg/amutex"
+	"gvisor.dev/gvisor/pkg/log"
+)
+
+type contextID int
+
+// Globally accessible values from a context. These keys are defined in the
+// context package to resolve dependency cycles by not requiring the caller to
+// import packages usually required to get these information.
+const (
+	// CtxThreadGroupID is the current thread group ID when a context represents
+	// a task context. The value is represented as an int32.
+	CtxThreadGroupID contextID = iota
+)
+
+// ThreadGroupIDFromContext returns the current thread group ID when ctx
+// represents a task context.
+func ThreadGroupIDFromContext(ctx Context) (tgid int32, ok bool) {
+	if tgid := ctx.Value(CtxThreadGroupID); tgid != nil {
+		return tgid.(int32), true
+	}
+	return 0, false
+}
+
+// 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
+	context.Context
+
+	// 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)
+}
+
+// NoopSleeper is a noop implementation of amutex.Sleeper and UninterruptibleSleep
+// methods for anonymous embedding in other types that do not implement sleeps.
+type NoopSleeper struct {
+	amutex.NoopSleeper
+}
+
+// UninterruptibleSleepStart does nothing.
+func (NoopSleeper) UninterruptibleSleepStart(bool) {}
+
+// UninterruptibleSleepFinish does nothing.
+func (NoopSleeper) UninterruptibleSleepFinish(bool) {}
+
+// Deadline returns zero values, meaning no deadline.
+func (NoopSleeper) Deadline() (time.Time, bool) {
+	return time.Time{}, false
+}
+
+// Done returns nil.
+func (NoopSleeper) Done() <-chan struct{} {
+	return nil
+}
+
+// Err returns nil.
+func (NoopSleeper) Err() error {
+	return nil
+}
+
+// logContext implements basic logging.
+type logContext struct {
+	log.Logger
+	NoopSleeper
+}
+
+// Value implements Context.Value.
+func (logContext) Value(key interface{}) interface{} {
+	return nil
+}
+
+// bgContext is the context returned by context.Background.
+var bgContext = &logContext{Logger: log.Log()}
+
+// Background returns an empty context using the default logger.
+//
+// Users should be wary of using a Background context. Please tag any use with
+// FIXME(b/38173783) 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 bgContext
+}