Add FileDescription interface for socket files.

Refactor the existing socket interface to share methods between VFS1 and VFS2.
The method signatures do not contain anything filesystem-related, so they don't
need to be re-defined for VFS2.

Updates #1476, #1478, #1484, #1485.

PiperOrigin-RevId: 304184545

pkg/sentry/socket/BUILD

@@ -16,6 +16,7 @@ go_library(
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/time",
         "//pkg/sentry/socket/unix/transport",
+        "//pkg/sentry/vfs",
         "//pkg/syserr",
         "//pkg/tcpip",
         "//pkg/usermem",

pkg/sentry/socket/socket.go

@@ -31,6 +31,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserr"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/usermem"
@@ -48,11 +49,25 @@ func (c *ControlMessages) Release() {
 	c.Unix.Release()
 }
 
-// Socket is the interface containing socket syscalls used by the syscall layer
-// to redirect them to the appropriate implementation.
+// Socket is an interface combining fs.FileOperations and SocketOps,
+// representing a VFS1 socket file.
 type Socket interface {
 	fs.FileOperations
+	SocketOps
+}
 
+// SocketVFS2 is an interface combining vfs.FileDescription and SocketOps,
+// representing a VFS2 socket file.
+type SocketVFS2 interface {
+	vfs.FileDescriptionImpl
+	SocketOps
+}
+
+// SocketOps is the interface containing socket syscalls used by the syscall
+// layer to redirect them to the appropriate implementation.
+//
+// It is implemented by both Socket and SocketVFS2.
+type SocketOps interface {
 	// Connect implements the connect(2) linux syscall.
 	Connect(t *kernel.Task, sockaddr []byte, blocking bool) *syserr.Error
 
@@ -153,6 +168,8 @@ var families = make(map[int][]Provider)
 // RegisterProvider registers the provider of a given address family so that
 // sockets of that type can be created via socket() and/or socketpair()
 // syscalls.
+//
+// This should only be called during the initialization of the address family.
 func RegisterProvider(family int, provider Provider) {
 	families[family] = append(families[family], provider)
 }
@@ -216,6 +233,72 @@ func NewDirent(ctx context.Context, d *device.Device) *fs.Dirent {
 	return fs.NewDirent(ctx, inode, fmt.Sprintf("socket:[%d]", ino))
 }
 
+// ProviderVFS2 is the vfs2 interface implemented by providers of sockets for
+// specific address families (e.g., AF_INET).
+type ProviderVFS2 interface {
+	// Socket creates a new socket.
+	//
+	// If a nil Socket _and_ a nil error is returned, it means that the
+	// protocol is not supported. A non-nil error should only be returned
+	// if the protocol is supported, but an error occurs during creation.
+	Socket(t *kernel.Task, stype linux.SockType, protocol int) (*vfs.FileDescription, *syserr.Error)
+
+	// Pair creates a pair of connected sockets.
+	//
+	// See Socket for error information.
+	Pair(t *kernel.Task, stype linux.SockType, protocol int) (*vfs.FileDescription, *vfs.FileDescription, *syserr.Error)
+}
+
+// familiesVFS2 holds a map of all known address families and their providers.
+var familiesVFS2 = make(map[int][]ProviderVFS2)
+
+// RegisterProviderVFS2 registers the provider of a given address family so that
+// sockets of that type can be created via socket() and/or socketpair()
+// syscalls.
+//
+// This should only be called during the initialization of the address family.
+func RegisterProviderVFS2(family int, provider ProviderVFS2) {
+	familiesVFS2[family] = append(familiesVFS2[family], provider)
+}
+
+// NewVFS2 creates a new socket with the given family, type and protocol.
+func NewVFS2(t *kernel.Task, family int, stype linux.SockType, protocol int) (*vfs.FileDescription, *syserr.Error) {
+	for _, p := range familiesVFS2[family] {
+		s, err := p.Socket(t, stype, protocol)
+		if err != nil {
+			return nil, err
+		}
+		if s != nil {
+			// TODO: Add vfs2 sockets to global socket table.
+			return s, nil
+		}
+	}
+
+	return nil, syserr.ErrAddressFamilyNotSupported
+}
+
+// PairVFS2 creates a new connected socket pair with the given family, type and
+// protocol.
+func PairVFS2(t *kernel.Task, family int, stype linux.SockType, protocol int) (*vfs.FileDescription, *vfs.FileDescription, *syserr.Error) {
+	providers, ok := familiesVFS2[family]
+	if !ok {
+		return nil, nil, syserr.ErrAddressFamilyNotSupported
+	}
+
+	for _, p := range providers {
+		s1, s2, err := p.Pair(t, stype, protocol)
+		if err != nil {
+			return nil, nil, err
+		}
+		if s1 != nil && s2 != nil {
+			// TODO: Add vfs2 sockets to global socket table.
+			return s1, s2, nil
+		}
+	}
+
+	return nil, nil, syserr.ErrSocketNotSupported
+}
+
 // SendReceiveTimeout stores timeouts for send and receive calls.
 //
 // It is meant to be embedded into Socket implementations to help satisfy the