Split VFS.MountAt into VFS.MountDisconnected and VFS.ConnectMountAt.

This makes it straightforward to create bind mounts internally in VFS2: Given a
bind mount root represented by vfs.VirtualDentry vd:

- Create a new mount with VFS.NewDisconnectedMount(vd.Mount().Filesystem(),
  vd.Dentry()).

- Connect the resulting mount in the appropriate namespace with
  VFS.ConnectMountAt().

Note that the resulting bind mount is non-recursive; recursive bind mounting
requires explicitly duplicating all children of the original mount, which is
best handled internally by VFS.

Updates #179

PiperOrigin-RevId: 313703963

1 files changed, 4 insertions, 0 deletions

diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 8d7f8f8af..6d2ba53ea 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -82,6 +82,10 @@ type VirtualFilesystem struct {
 	// mountpoints is analogous to Linux's mountpoint_hashtable.
 	mountpoints map[*Dentry]map[*Mount]struct{}
 
+	// lastMountID is the last allocated mount ID. lastMountID is accessed
+	// using atomic memory operations.
+	lastMountID uint64
+
 	// anonMount is a Mount, not included in mounts or mountpoints,
 	// representing an anonFilesystem. anonMount is used to back
 	// VirtualDentries returned by VirtualFilesystem.NewAnonVirtualDentry().