Skip dirents that fail stat(2) during Getdents RPC.

A file might disappear in between the call to unix.Getdents() and unix.Stat().
We should simply skip these files while returning the results for Getdents RPC
instead of failing the entire RPC. This is consistent with what 9P fsgofer.

This was causing <0.1% flake rate for lisafs syscall tests on BuildKite.

PiperOrigin-RevId: 433606841

pkg/lisafs/node.go

@@ -169,7 +169,9 @@ func (n *Node) WithChildrenMu(fn func()) {
 // operation. The returned path should be free of any intermediate symlinks
 // because all internal (non-leaf) nodes are directories.
 //
-// Precondition: server's rename mutex must be at least read locked.
+// Precondition:
+// * server's rename mutex must be at least read locked. Calling handlers must
+//   at least have read concurrency guarantee from the server.
 func (n *Node) FilePath() string {
 	// Walk upwards and prepend name to res.
 	var res fspath.Builder

runsc/boot/vfs.go

@@ -685,7 +685,7 @@ func (c *containerMounter) mountTmpVFS2(ctx context.Context, conf *config.Config
 			log.Infof(`Skipping internal tmpfs mount for "/tmp" because it's not empty`)
 			return nil
 		default:
-			return err
+			return fmt.Errorf("fd.IterDirents failed: %v", err)
 		}
 		fallthrough
 
@@ -699,8 +699,10 @@ func (c *containerMounter) mountTmpVFS2(ctx context.Context, conf *config.Config
 			// another user. This is normally done for /tmp.
 			Options: []string{"mode=01777"},
 		}
-		_, err := c.mountSubmountVFS2(ctx, conf, mns, creds, &mountAndFD{mount: &tmpMount})
-		return err
+		if _, err := c.mountSubmountVFS2(ctx, conf, mns, creds, &mountAndFD{mount: &tmpMount}); err != nil {
+			return fmt.Errorf("mountSubmountVFS2 failed: %v", err)
+		}
+		return nil
 
 	case linuxerr.Equals(linuxerr.ENOTDIR, err):
 		// Not a dir?! Let it be.

runsc/fsgofer/fsgofer.go

@@ -1096,7 +1096,7 @@ func (l *localFile) readDirent(f int, offset uint64, count uint32, skip uint64)
 		for _, name := range names {
 			stat, err := statAt(l.file.FD(), name)
 			if err != nil {
-				log.Warningf("Readdir is skipping file with failed stat %q, err: %v", l.hostPath, err)
+				log.Warningf("Readdir is skipping file %q with failed stat, err: %v", path.Join(l.hostPath, name), err)
 				continue
 			}
 			qid := l.attachPoint.makeQID(&stat)

runsc/fsgofer/lisafs.go

@@ -809,7 +809,6 @@ func (fd *openFDLisa) Getdent64(count uint32, seek0 bool, recordDirent func(lisa
 		}
 		bytesRead += n
 
-		var statErr error
 		parseDirents(direntsBuf[:n], func(ino uint64, off int64, ftype uint8, name string) bool {
 			dirent := lisafs.Dirent64{
 				Ino:  primitive.Uint64(ino),
@@ -822,17 +821,14 @@ func (fd *openFDLisa) Getdent64(count uint32, seek0 bool, recordDirent func(lisa
 			// additional syscall per dirent. Live with it.
 			stat, err := statAt(fd.hostFD, name)
 			if err != nil {
-				statErr = err
-				return false
+				log.Warningf("Getdent64: skipping file %q with failed stat, err: %v", path.Join(fd.ControlFD().FD().Node().FilePath(), name), err)
+				return true
 			}
 			dirent.DevMinor = primitive.Uint32(unix.Minor(stat.Dev))
 			dirent.DevMajor = primitive.Uint32(unix.Major(stat.Dev))
 			recordDirent(dirent)
 			return true
 		})
-		if statErr != nil {
-			return statErr
-		}
 	}
 	return nil
 }