Implement mount(2) and umount2(2) for VFS2.

This is mostly syscall plumbing, VFS2 already implements the internals of
mounts. In addition to the syscall defintions, the following mount-related
mechanisms are updated:

- Implement MS_NOATIME for VFS2, but only for tmpfs and goferfs. The other VFS2
  filesystems don't implement node-level timestamps yet.

- Implement the 'mode', 'uid' and 'gid' mount options for VFS2's tmpfs.

- Plumb mount namespace ownership, which is necessary for checking appropriate
  capabilities during mount(2).

Updates #1035

PiperOrigin-RevId: 315035352

1 files changed, 3 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/gofer/time.go b/pkg/sentry/fsimpl/gofer/time.go
index 2608e7e1d..1d5aa82dc 100644
--- a/pkg/sentry/fsimpl/gofer/time.go
+++ b/pkg/sentry/fsimpl/gofer/time.go
@@ -38,6 +38,9 @@ func statxTimestampFromDentry(ns int64) linux.StatxTimestamp {
 
 // Preconditions: fs.interop != InteropModeShared.
 func (d *dentry) touchAtime(mnt *vfs.Mount) {
+	if mnt.Flags.NoATime {
+		return
+	}
 	if err := mnt.CheckBeginWrite(); err != nil {
 		return
 	}