Implement queueInode and queueFD in mqfs.

Implement inode and file description representing a POSIX message queue,
and other utilities needed to implement file operations.

Updates #136

1 files changed, 83 insertions, 1 deletions

diff --git a/pkg/sentry/kernel/mq/mq.go b/pkg/sentry/kernel/mq/mq.go
index df9bdc267..29a46e8a9 100644
--- a/pkg/sentry/kernel/mq/mq.go
+++ b/pkg/sentry/kernel/mq/mq.go
@@ -16,7 +16,11 @@
 package mq
 
 import (
+	"bytes"
+	"fmt"
+
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/waiter"
@@ -52,7 +56,7 @@ type Queue struct {
 
 	// subscriber represents a task registered to receive async notification
 	// from this queue.
-	subscriber Subscriber
+	subscriber *Subscriber
 
 	// nonBlock is true if this queue is non-blocking.
 	nonBlock bool
@@ -93,4 +97,82 @@ type Message struct {
 // +stateify savable
 type Subscriber struct {
 	// TODO: Add fields when mq_notify(2) is implemented.
+
+	// pid is the PID of the registered task.
+	pid int32
+}
+
+// Generate implements vfs.DynamicBytesSource.Generate. Queue is used as a
+// dynamic bytes source for mqfs's queueInode.
+func (q *Queue) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	var (
+		pid       int32
+		method    int
+		sigNumber int
+	)
+	if q.subscriber != nil {
+		pid = q.subscriber.pid
+		// TODO: add method and sigNumber when mq_notify(2) is implemented.
+	}
+
+	buf.WriteString(
+		fmt.Sprintf("QSIZE:%-10d NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d\n",
+			q.byteCount, method, sigNumber, pid),
+	)
+	return nil
+}
+
+// Flush checks if the calling process has attached a notification request to
+// this queue, if yes, then the request is removed, and another process can
+// attach a request.
+func (q *Queue) Flush(ctx context.Context) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	pid, ok := context.ThreadGroupIDFromContext(ctx)
+	if ok {
+		if q.subscriber != nil && pid == q.subscriber.pid {
+			q.subscriber = nil
+		}
+	}
+}
+
+// Readiness implements Waitable.Readiness.
+func (q *Queue) Readiness(mask waiter.EventMask) waiter.EventMask {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	events := waiter.EventMask(0)
+	if q.messageCount > 0 {
+		events |= waiter.ReadableEvents
+	}
+	if q.messageCount < q.maxMessageCount {
+		events |= waiter.WritableEvents
+	}
+	return events & mask
+}
+
+// EventRegister implements Waitable.EventRegister.
+func (q *Queue) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	if mask&waiter.WritableEvents != 0 {
+		q.senders.EventRegister(e, waiter.EventOut)
+	}
+	if mask&waiter.ReadableEvents != 0 {
+		q.receivers.EventRegister(e, waiter.EventIn)
+	}
+}
+
+// EventUnregister implements Waitable.EventUnregister.
+func (q *Queue) EventUnregister(e *waiter.Entry) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	q.senders.EventUnregister(e)
+	q.receivers.EventUnregister(e)
 }