posixtest: print more infos on fd leak

gocryptfs has a similar test with somewhat more detailed
parsing of the open fds. Import the ListFds function from
gocryptfs and use it to make the error more informative.

Change-Id: I2442364e2e5d49749683072b91bda5691ad8902e

posixtest/listfds.go

+// Copyright 2019 the Go-FUSE Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package posixtest file systems for generic posix conformance.
+package posixtest
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"runtime"
+	"strings"
+)
+
+// listFds lists the open file descriptors for process "pid". Pass pid=0 for
+// ourselves. Pass a prefix to ignore all paths that do not start with "prefix".
+//
+// Copied from https://github.com/rfjakob/gocryptfs/blob/master/tests/test_helpers/mount_unmount.go#L191
+func listFds(pid int, prefix string) []string {
+	// We need /proc to get the list of fds for other processes. Only exists
+	// on Linux.
+	if runtime.GOOS != "linux" && pid > 0 {
+		return nil
+	}
+	// Both Linux and MacOS have /dev/fd
+	dir := "/dev/fd"
+	if pid > 0 {
+		dir = fmt.Sprintf("/proc/%d/fd", pid)
+	}
+	f, err := os.Open(dir)
+	if err != nil {
+		fmt.Printf("ListFds: %v\n", err)
+		return nil
+	}
+	defer f.Close()
+	// Note: Readdirnames filters "." and ".."
+	names, err := f.Readdirnames(0)
+	if err != nil {
+		log.Panic(err)
+	}
+	var out []string
+	var filtered []string
+	for _, n := range names {
+		fdPath := dir + "/" + n
+		fi, err := os.Lstat(fdPath)
+		if err != nil {
+			// fd was closed in the meantime
+			continue
+		}
+		if fi.Mode()&0400 > 0 {
+			n += "r"
+		}
+		if fi.Mode()&0200 > 0 {
+			n += "w"
+		}
+		target, err := os.Readlink(fdPath)
+		if err != nil {
+			// fd was closed in the meantime
+			continue
+		}
+		if strings.HasPrefix(target, "pipe:") || strings.HasPrefix(target, "anon_inode:[eventpoll]") {
+			// go-fuse creates pipes on demand for splice(), which
+			// creates spurious test failures. Ignore all pipes.
+			// Also get rid of the "eventpoll" fd that is always there and not
+			// interesting.
+			filtered = append(filtered, target)
+			continue
+		}
+		if prefix != "" && !strings.HasPrefix(target, prefix) {
+			filtered = append(filtered, target)
+			continue
+		}
+		out = append(out, n+"="+target)
+	}
+	out = append(out, fmt.Sprintf("(filtered: %s)", strings.Join(filtered, ", ")))
+	return out
+}

posixtest/test.go

@@ -150,13 +150,9 @@ func FdLeak(t *testing.T, mnt string) {
 	}
 
 	if runtime.GOOS == "linux" {
-		infos, err := ioutil.ReadDir("/proc/self/fd")
-		if err != nil {
-			t.Errorf("ReadDir %v", err)
-		}
-
+		infos := listFds(0, "")
 		if len(infos) > 15 {
-			t.Errorf("found %d open file descriptors for 100x ReadFile", len(infos))
+			t.Errorf("found %d open file descriptors for 100x ReadFile: %v", len(infos), infos)
 		}
 	}
 }