Implement POSIX locks

- Change FileDescriptionImpl Lock/UnlockPOSIX signature to
  take {start,length,whence}, so the correct offset can be
  calculated in the implementations.
- Create PosixLocker interface to make it possible to share
  the same locking code from different implementations.

Closes #1480

PiperOrigin-RevId: 316910286

pkg/sentry/socket/netstack/BUILD

@@ -28,6 +28,7 @@ go_library(
         "//pkg/sentry/device",
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/fsutil",
+        "//pkg/sentry/fs/lock",
         "//pkg/sentry/fsimpl/sockfs",
         "//pkg/sentry/inet",
         "//pkg/sentry/kernel",
@@ -37,7 +38,6 @@ go_library(
         "//pkg/sentry/socket/netfilter",
         "//pkg/sentry/unimpl",
         "//pkg/sentry/vfs",
-        "//pkg/sentry/vfs/lock",
         "//pkg/sync",
         "//pkg/syserr",
         "//pkg/syserror",

pkg/sentry/socket/netstack/netstack_vfs2.go

@@ -19,13 +19,13 @@ import (
 	"gvisor.dev/gvisor/pkg/amutex"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	fslock "gvisor.dev/gvisor/pkg/sentry/fs/lock"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/sockfs"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/socket"
 	"gvisor.dev/gvisor/pkg/sentry/socket/netfilter"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
-	"gvisor.dev/gvisor/pkg/sentry/vfs/lock"
 	"gvisor.dev/gvisor/pkg/syserr"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -66,7 +66,7 @@ func NewVFS2(t *kernel.Task, family int, skType linux.SockType, protocol int, qu
 			protocol: protocol,
 		},
 	}
-	s.LockFD.Init(&lock.FileLocks{})
+	s.LockFD.Init(&vfs.FileLocks{})
 	vfsfd := &s.vfsfd
 	if err := vfsfd.Init(s, linux.O_RDWR, mnt, d, &vfs.FileDescriptionOptions{
 		DenyPRead:         true,
@@ -318,3 +318,13 @@ func (s *SocketVFS2) SetSockOpt(t *kernel.Task, level int, name int, optVal []by
 
 	return SetSockOpt(t, s, s.Endpoint, level, name, optVal)
 }
+
+// LockPOSIX implements vfs.FileDescriptionImpl.LockPOSIX.
+func (s *SocketVFS2) LockPOSIX(ctx context.Context, uid fslock.UniqueID, t fslock.LockType, start, length uint64, whence int16, block fslock.Blocker) error {
+	return s.Locks().LockPOSIX(ctx, &s.vfsfd, uid, t, start, length, whence, block)
+}
+
+// UnlockPOSIX implements vfs.FileDescriptionImpl.UnlockPOSIX.
+func (s *SocketVFS2) UnlockPOSIX(ctx context.Context, uid fslock.UniqueID, start, length uint64, whence int16) error {
+	return s.Locks().UnlockPOSIX(ctx, &s.vfsfd, uid, start, length, whence)
+}