HACK to make /dev/tty work.

We need to plumb the host.TTYFileDescription into the /dev/tty device file.

This is *not* the correct way to do it, but it does allow emacs to work.

Updates #10925

DO NOT SUBMIT

PiperOrigin-RevId: 676585154

Author: nlacasse

pkg/sentry/devices/ttydev/ttydev.go

@@ -22,6 +22,9 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 )
 
+// TTYFile is a HACK.
+var TTYFile *vfs.FileDescription
+
 const (
 	// See drivers/tty/tty_io.c:tty_init().
 	ttyDevMinor     = 0
@@ -35,6 +38,9 @@ type ttyDevice struct{}
 
 // Open implements vfs.Device.Open.
 func (ttyDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	if TTYFile != nil {
+		return TTYFile, nil
+	}
 	return nil, linuxerr.EIO
 }
 

pkg/sentry/fdimport/BUILD

@@ -14,6 +14,7 @@ go_library(
     deps = [
         "//pkg/context",
         "//pkg/fd",
+        "//pkg/sentry/devices/ttydev",
         "//pkg/sentry/fsimpl/host",
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",

pkg/sentry/fdimport/fdimport.go

@@ -21,6 +21,7 @@ import (
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fd"
+	"gvisor.dev/gvisor/pkg/sentry/devices/ttydev"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -106,6 +107,8 @@ func Import(ctx context.Context, fdTable *kernel.FDTable, console bool, uid auth
 	if ttyFile == nil {
 		return nil, nil
 	}
+	// HACK.
+	ttydev.TTYFile = ttyFile
 	return ttyFile.Impl().(*host.TTYFileDescription), nil
 }