Add anonymous device number allocation to VFS2.

Note that in VFS2, filesystem device numbers are per-vfs.FilesystemImpl rather
than global, avoiding the need for a "registry" type to handle save/restore.
(This is more consistent with Linux anyway: compare e.g.
mm/shmem.c:shmem_mount() => fs/super.c:mount_nodev() => (indirectly)
set_anon_super().)

PiperOrigin-RevId: 291425193

1 files changed, 14 insertions, 4 deletions

diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 1f21b0b31..1f6f56293 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -80,6 +80,14 @@ type VirtualFilesystem struct {
 	devicesMu sync.RWMutex
 	devices   map[devTuple]*registeredDevice
 
+	// anonBlockDevMinor contains all allocated anonymous block device minor
+	// numbers. anonBlockDevMinorNext is a lower bound for the smallest
+	// unallocated anonymous block device number. anonBlockDevMinorNext and
+	// anonBlockDevMinor are protected by anonBlockDevMinorMu.
+	anonBlockDevMinorMu   sync.Mutex
+	anonBlockDevMinorNext uint32
+	anonBlockDevMinor     map[uint32]struct{}
+
 	// fsTypes contains all registered FilesystemTypes. fsTypes is protected by
 	// fsTypesMu.
 	fsTypesMu sync.RWMutex
@@ -94,10 +102,12 @@ type VirtualFilesystem struct {
 // New returns a new VirtualFilesystem with no mounts or FilesystemTypes.
 func New() *VirtualFilesystem {
 	vfs := &VirtualFilesystem{
-		mountpoints: make(map[*Dentry]map[*Mount]struct{}),
-		devices:     make(map[devTuple]*registeredDevice),
-		fsTypes:     make(map[string]*registeredFilesystemType),
-		filesystems: make(map[*Filesystem]struct{}),
+		mountpoints:           make(map[*Dentry]map[*Mount]struct{}),
+		devices:               make(map[devTuple]*registeredDevice),
+		anonBlockDevMinorNext: 1,
+		anonBlockDevMinor:     make(map[uint32]struct{}),
+		fsTypes:               make(map[string]*registeredFilesystemType),
+		filesystems:           make(map[*Filesystem]struct{}),
 	}
 	vfs.mounts.Init()
 	return vfs