Move hostfs mount to Kernel struct.

This is needed to set up host fds passed through a Unix socket. Note that
the host package depends on kernel, so we cannot set up the hostfs mount
directly in Kernel.Init as we do for sockfs and pipefs.

Also, adjust sockfs to make its setup look more like hostfs's and pipefs's.

PiperOrigin-RevId: 308274053

2 files changed, 14 insertions, 6 deletions

diff --git a/runsc/boot/fds.go b/runsc/boot/fds.go
index 7e49f6f9f..0cbd63857 100644
--- a/runsc/boot/fds.go
+++ b/runsc/boot/fds.go
@@ -89,14 +89,9 @@ func createFDTableVFS2(ctx context.Context, console bool, stdioFDs []int) (*kern
 	fdTable := k.NewFDTable()
 	defer fdTable.DecRef()
 
-	hostMount, err := vfshost.NewMount(k.VFS())
-	if err != nil {
-		return nil, fmt.Errorf("creating host mount: %w", err)
-	}
-
 	for appFD, hostFD := range stdioFDs {
 		// TODO(gvisor.dev/issue/1482): Add TTY support.
-		appFile, err := vfshost.ImportFD(hostMount, hostFD, false)
+		appFile, err := vfshost.ImportFD(k.HostMount(), hostFD, false)
 		if err != nil {
 			return nil, err
 		}
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 096b0e9f0..3f41d8357 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -36,6 +36,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/fs/host"
 	"gvisor.dev/gvisor/pkg/sentry/fs/user"
+	vfs2host "gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -46,6 +47,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/syscalls/linux/vfs2"
 	"gvisor.dev/gvisor/pkg/sentry/time"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sentry/watchdog"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -329,6 +331,17 @@ func New(args Args) (*Loader, error) {
 		return nil, fmt.Errorf("creating pod mount hints: %v", err)
 	}
 
+	if kernel.VFS2Enabled {
+		// Set up host mount that will be used for imported fds.
+		hostFilesystem := vfs2host.NewFilesystem(k.VFS())
+		defer hostFilesystem.DecRef()
+		hostMount, err := k.VFS().NewDisconnectedMount(hostFilesystem, nil, &vfs.MountOptions{})
+		if err != nil {
+			return nil, fmt.Errorf("failed to create hostfs mount: %v", err)
+		}
+		k.SetHostMount(hostMount)
+	}
+
 	// Make host FDs stable between invocations. Host FDs must map to the exact
 	// same number when the sandbox is restored. Otherwise the wrong FD will be
 	// used.