db: Add BackingType, Locator to SSTableInfo

The SSTables() method returns sstable info from a Pebble
db instance. This change adds an additional field denoting
the type of storage backing a given sstable in addition to
all other sstable properties; i.e. whether an sstable is
local, shared (non-foreign), shared+foreign, or external.
It also adds a field denoting the shared.Locator, if one
was specified.

db.go

@@ -23,6 +23,7 @@ import (
 	"github.com/cockroachdb/pebble/internal/manifest"
 	"github.com/cockroachdb/pebble/internal/manual"
 	"github.com/cockroachdb/pebble/objstorage"
+	"github.com/cockroachdb/pebble/objstorage/shared"
 	"github.com/cockroachdb/pebble/rangekey"
 	"github.com/cockroachdb/pebble/record"
 	"github.com/cockroachdb/pebble/sstable"
@@ -1904,7 +1905,30 @@ func WithApproximateSpanBytes() SSTablesOption {
 	}
 }
 
-// SSTableInfo export manifest.TableInfo with sstable.Properties
+// BackingType denotes the type of storage backing a given sstable.
+type BackingType int
+
+const (
+	// BackingTypeLocal denotes an sstable stored on local disk according to the
+	// objprovider. This file is completely owned by us.
+	BackingTypeLocal BackingType = iota
+	// BackingTypeShared denotes an sstable stored on shared storage, created
+	// by this Pebble instance and possibly shared by other Pebble instances.
+	// These types of files have lifecycle managed by Pebble.
+	BackingTypeShared
+	// BackingTypeSharedForeign denotes an sstable stored on shared storage,
+	// created by a Pebble instance other than this one. These types of files have
+	// lifecycle managed by Pebble.
+	BackingTypeSharedForeign
+	// BackingTypeExternal denotes an sstable stored on external storage,
+	// not owned by any Pebble instance and with no refcounting/cleanup methods
+	// or lifecycle management. An example of an external file is a file restored
+	// from a backup.
+	BackingTypeExternal
+)
+
+// SSTableInfo export manifest.TableInfo with sstable.Properties alongside
+// other file backing info.
 type SSTableInfo struct {
 	manifest.TableInfo
 	// Virtual indicates whether the sstable is virtual.
@@ -1913,6 +1937,11 @@ type SSTableInfo struct {
 	// backs the sstable associated with this SSTableInfo. If Virtual is false,
 	// then BackingSSTNum == FileNum.
 	BackingSSTNum base.FileNum
+	// BackingType is the type of storage backing this sstable.
+	BackingType BackingType
+	// Locator is the shared.Locator backing this sstable, if one was specified
+	// during ingest.
+	Locator shared.Locator
 
 	// Properties is the sstable properties of this table. If Virtual is true,
 	// then the Properties are associated with the backing sst.
@@ -1972,6 +2001,22 @@ func (d *DB) SSTables(opts ...SSTablesOption) ([][]SSTableInfo, error) {
 			}
 			destTables[j].Virtual = m.Virtual
 			destTables[j].BackingSSTNum = m.FileBacking.DiskFileNum.FileNum()
+			objMeta, err := d.objProvider.Lookup(fileTypeTable, m.FileBacking.DiskFileNum)
+			if err != nil {
+				return nil, err
+			}
+			if objMeta.IsShared() {
+				if d.objProvider.IsForeign(objMeta) {
+					destTables[j].BackingType = BackingTypeSharedForeign
+				} else if objMeta.Shared.CleanupMethod == objstorage.SharedNoCleanup {
+					destTables[j].BackingType = BackingTypeExternal
+				} else {
+					destTables[j].BackingType = BackingTypeShared
+				}
+				destTables[j].Locator = objMeta.Shared.Locator
+			} else {
+				destTables[j].BackingType = BackingTypeLocal
+			}
 
 			if opt.withApproximateSpanBytes {
 				var spanBytes uint64