Initial support for bind mounts

Separate MountSource from Mount. This is needed to allow
mounts to be shared by multiple containers within the same
pod.

PiperOrigin-RevId: 249617810
Change-Id: Id2944feb7e4194951f355cbe6d4944ae3c02e468

1 files changed, 1 insertions, 72 deletions

diff --git a/pkg/sentry/fs/mount.go b/pkg/sentry/fs/mount.go
index 63fcf4380..41e0d285b 100644
--- a/pkg/sentry/fs/mount.go
+++ b/pkg/sentry/fs/mount.go
@@ -17,7 +17,6 @@ package fs
 import (
 	"bytes"
 	"fmt"
-	"sync"
 	"sync/atomic"
 
 	"gvisor.googlesource.com/gvisor/pkg/refs"
@@ -89,15 +88,7 @@ func (i InodeMappings) String() string {
 // one mount source. Each file object may only be represented using one inode
 // object in a sentry instance.
 //
-// This is an amalgamation of structs super_block, vfsmount, and mount, while
-// MountSourceOperations is akin to struct super_operations.
-//
-// Hence, mount source also contains common mounted file system state, such as
-// mount flags, the root Dirent, and children mounts. For now, this
-// amalgamation implies that a mount source cannot be shared by multiple mounts
-// (e.g. cannot be mounted at different locations).
-//
-// TODO(b/63601033): Move mount-specific information out of MountSource.
+// TODO(b/63601033): Move Flags out of MountSource to Mount.
 //
 // +stateify savable
 type MountSource struct {
@@ -128,22 +119,6 @@ type MountSource struct {
 	//
 	// direntRefs must be atomically changed.
 	direntRefs uint64
-
-	// mu protects the fields below, which are set by the MountNamespace
-	// during MountSource/Unmount.
-	mu sync.Mutex `state:"nosave"`
-
-	// id is a unique id for this mount.
-	id uint64
-
-	// root is the root Dirent of this mount.
-	root *Dirent
-
-	// parent is the parent MountSource, or nil if this MountSource is the root.
-	parent *MountSource
-
-	// children are the child MountSources of this MountSource.
-	children map[*MountSource]struct{}
 }
 
 // DefaultDirentCacheSize is the number of Dirents that the VFS can hold an
@@ -162,53 +137,7 @@ func NewMountSource(mops MountSourceOperations, filesystem Filesystem, flags Mou
 		Flags:                 flags,
 		FilesystemType:        fsType,
 		fscache:               NewDirentCache(DefaultDirentCacheSize),
-		children:              make(map[*MountSource]struct{}),
-	}
-}
-
-// Parent returns the parent mount, or nil if this mount is the root.
-func (msrc *MountSource) Parent() *MountSource {
-	msrc.mu.Lock()
-	defer msrc.mu.Unlock()
-	return msrc.parent
-}
-
-// ID returns the ID of this mount.
-func (msrc *MountSource) ID() uint64 {
-	msrc.mu.Lock()
-	defer msrc.mu.Unlock()
-	return msrc.id
-}
-
-// Children returns the (immediate) children of this MountSource.
-func (msrc *MountSource) Children() []*MountSource {
-	msrc.mu.Lock()
-	defer msrc.mu.Unlock()
-
-	ms := make([]*MountSource, 0, len(msrc.children))
-	for c := range msrc.children {
-		ms = append(ms, c)
 	}
-	return ms
-}
-
-// Submounts returns all mounts that are descendants of this mount.
-func (msrc *MountSource) Submounts() []*MountSource {
-	var ms []*MountSource
-	for _, c := range msrc.Children() {
-		ms = append(ms, c)
-		ms = append(ms, c.Submounts()...)
-	}
-	return ms
-}
-
-// Root returns the root dirent of this mount. Callers must call DecRef on the
-// returned dirent.
-func (msrc *MountSource) Root() *Dirent {
-	msrc.mu.Lock()
-	defer msrc.mu.Unlock()
-	msrc.root.IncRef()
-	return msrc.root
 }
 
 // DirentRefs returns the current mount direntRefs.