Allow lisafs server to open on deleted files in runsc gofer.

Updates the lisafs server to provide an option for allowing opening files which
have been deleted in the filesystem.

This is needed for save/restore of deleted files which don't have a readable
handle open for them and a readable handle needs to be opened to read the
contents of the file, which needs to be saved.

Updates #11903

PiperOrigin-RevId: 784249243

Author: ayushr2

pkg/lisafs/handlers.go

@@ -527,7 +527,10 @@ func OpenAtHandler(c *Connection, comm Communicator, payloadLen uint32) (uint32,
 		hostOpenFD int
 	)
 	if err := fd.safelyRead(func() error {
-		if fd.node.isDeleted() || fd.IsSymlink() {
+		if fd.node.isDeleted() && !c.server.opts.OpenOnDeleted {
+			return unix.EINVAL
+		}
+		if fd.IsSymlink() {
 			return unix.EINVAL
 		}
 		openFD, hostOpenFD, err = fd.impl.Open(req.Flags)

pkg/lisafs/server.go

@@ -62,6 +62,10 @@ type ServerOpts struct {
 	// AllocateOnDeleted is set to true if it's safe to call OpenFDImpl.Allocate
 	// for deleted files.
 	AllocateOnDeleted bool
+
+	// OpenOnDeleted is set to true if it's safe to call ControlFDImpl.Open for
+	// deleted files.
+	OpenOnDeleted bool
 }
 
 // Init must be called before first use of the server.

runsc/fsgofer/lisafs.go

@@ -107,6 +107,7 @@ func NewLisafsServer(config Config) *LisafsServer {
 		WalkStatSupported: true,
 		SetAttrOnDeleted:  true,
 		AllocateOnDeleted: true,
+		OpenOnDeleted:     true,
 	})
 	return s
 }