Use Readdirnames to reduce number of stats we're doing.

common/fs/fs.go

@@ -10,6 +10,7 @@ import (
 // Interface is the filesystem interface type.
 type Interface interface {
 	ReadDir(string) ([]os.FileInfo, error)
+	ReadDirNames(string) ([]string, error)
 	ReadFile(string) ([]byte, error)
 	Lstat(string, *syscall.Stat_t) error
 	Stat(string, *syscall.Stat_t) error
@@ -25,6 +26,15 @@ func (realFS) ReadDir(path string) ([]os.FileInfo, error) {
 	return ioutil.ReadDir(path)
 }
 
+func (realFS) ReadDirNames(path string) ([]string, error) {
+	fh, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer fh.Close()
+	return fh.Readdirnames(-1)
+}
+
 func (realFS) ReadFile(path string) ([]byte, error) {
 	return ioutil.ReadFile(path)
 }
@@ -48,6 +58,11 @@ func ReadDir(path string) ([]os.FileInfo, error) {
 	return fs.ReadDir(path)
 }
 
+// ReadDirNames see os.File.ReadDirNames
+func ReadDirNames(path string) ([]string, error) {
+	return fs.ReadDirNames(path)
+}
+
 // ReadFile see ioutil.ReadFile
 func ReadFile(path string) ([]byte, error) {
 	return fs.ReadFile(path)

probe/endpoint/procspy/proc.go

@@ -34,15 +34,10 @@ func walkProcPid(buf *bytes.Buffer, walker process.Walker) (map[uint64]Proc, err
 	walker.Walk(func(p process.Process) {
 		dirName := strconv.Itoa(p.PID)
 		fdBase := filepath.Join(procRoot, dirName, "fd")
-		fds, err := fs.ReadDir(fdBase)
-		if err != nil {
-			// Process is be gone by now, or we don't have access.
-			return
-		}
 
 		// Read network namespace, and if we haven't seen it before,
 		// read /proc/<pid>/net/tcp
-		err = fs.Lstat(filepath.Join(procRoot, dirName, "/ns/net"), &statT)
+		err := fs.Lstat(filepath.Join(procRoot, dirName, "/ns/net"), &statT)
 		if err != nil {
 			return
 		}
@@ -53,9 +48,14 @@ func walkProcPid(buf *bytes.Buffer, walker process.Walker) (map[uint64]Proc, err
 			readFile(filepath.Join(procRoot, dirName, "/net/tcp6"), buf)
 		}
 
+		fds, err := fs.ReadDirNames(fdBase)
+		if err != nil {
+			// Process is be gone by now, or we don't have access.
+			return
+		}
 		for _, fd := range fds {
 			// Direct use of syscall.Stat() to save garbage.
-			err = fs.Stat(filepath.Join(fdBase, fd.Name()), &statT)
+			err = fs.Stat(filepath.Join(fdBase, fd), &statT)
 			if err != nil {
 				continue
 			}

probe/process/walker_linux.go

@@ -23,13 +23,12 @@ func NewWalker(procRoot string) Walker {
 // passes one-by-one to the supplied function. Walk is only made public
 // so that is can be tested.
 func (w *walker) Walk(f func(Process)) error {
-	dirEntries, err := fs.ReadDir(w.procRoot)
+	dirEntries, err := fs.ReadDirNames(w.procRoot)
 	if err != nil {
 		return err
 	}
 
-	for _, dirEntry := range dirEntries {
-		filename := dirEntry.Name()
+	for _, filename := range dirEntries {
 		pid, err := strconv.Atoi(filename)
 		if err != nil {
 			continue

test/fs/fs.go

@@ -89,6 +89,24 @@ func (p dir) ReadDir(path string) ([]os.FileInfo, error) {
 	return fs.ReadDir(tail)
 }
 
+func (p dir) ReadDirNames(path string) ([]string, error) {
+	if path == "/" {
+		result := []string{}
+		for _, v := range p.entries {
+			result = append(result, v.Name())
+		}
+		return result, nil
+	}
+
+	head, tail := split(path)
+	fs, ok := p.entries[head]
+	if !ok {
+		return nil, fmt.Errorf("Not found: %s", path)
+	}
+
+	return fs.ReadDirNames(tail)
+}
+
 func (p dir) ReadFile(path string) ([]byte, error) {
 	if path == "/" {
 		return nil, fmt.Errorf("I'm a directory!")
@@ -156,6 +174,11 @@ func (p File) ReadDir(path string) ([]os.FileInfo, error) {
 	return nil, fmt.Errorf("I'm a file!")
 }
 
+// ReadDirNames implements FS
+func (p File) ReadDirNames(path string) ([]string, error) {
+	return nil, fmt.Errorf("I'm a file!")
+}
+
 // ReadFile implements FS
 func (p File) ReadFile(path string) ([]byte, error) {
 	if path != "/" {