diff --git a/cmd/derper/depaware.txt b/cmd/derper/depaware.txt index 0283c49ef..84ddb6a5f 100644 --- a/cmd/derper/depaware.txt +++ b/cmd/derper/depaware.txt @@ -34,7 +34,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa tailscale.com/hostinfo from tailscale.com/net/interfaces+ tailscale.com/ipn from tailscale.com/client/tailscale tailscale.com/ipn/ipnstate from tailscale.com/client/tailscale+ - 💣 tailscale.com/metrics from tailscale.com/cmd/derper+ + tailscale.com/metrics from tailscale.com/cmd/derper+ tailscale.com/net/dnscache from tailscale.com/derp/derphttp tailscale.com/net/flowtrack from tailscale.com/net/packet+ 💣 tailscale.com/net/interfaces from tailscale.com/net/netns+ @@ -72,6 +72,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa W tailscale.com/util/clientmetric from tailscale.com/net/tshttpproxy tailscale.com/util/cloudenv from tailscale.com/hostinfo+ W tailscale.com/util/cmpver from tailscale.com/net/tshttpproxy + L 💣 tailscale.com/util/dirwalk from tailscale.com/metrics tailscale.com/util/dnsname from tailscale.com/hostinfo+ W tailscale.com/util/endian from tailscale.com/net/netns tailscale.com/util/lineread from tailscale.com/hostinfo+ diff --git a/cmd/tailscale/depaware.txt b/cmd/tailscale/depaware.txt index c43ce78e9..0bc8504b9 100644 --- a/cmd/tailscale/depaware.txt +++ b/cmd/tailscale/depaware.txt @@ -52,7 +52,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep tailscale.com/hostinfo from tailscale.com/net/interfaces+ tailscale.com/ipn from tailscale.com/cmd/tailscale/cli+ tailscale.com/ipn/ipnstate from tailscale.com/cmd/tailscale/cli+ - 💣 tailscale.com/metrics from tailscale.com/derp + tailscale.com/metrics from tailscale.com/derp tailscale.com/net/dnscache from tailscale.com/derp/derphttp+ tailscale.com/net/dnsfallback from tailscale.com/control/controlhttp tailscale.com/net/flowtrack from tailscale.com/wgengine/filter+ @@ -95,6 +95,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep tailscale.com/util/clientmetric from tailscale.com/net/netcheck+ tailscale.com/util/cloudenv from tailscale.com/net/dnscache+ W tailscale.com/util/cmpver from tailscale.com/net/tshttpproxy + L 💣 tailscale.com/util/dirwalk from tailscale.com/metrics tailscale.com/util/dnsname from tailscale.com/cmd/tailscale/cli+ W tailscale.com/util/endian from tailscale.com/net/netns tailscale.com/util/groupmember from tailscale.com/cmd/tailscale/cli diff --git a/cmd/tailscaled/depaware.txt b/cmd/tailscaled/depaware.txt index 3ee8ba01b..65c67252f 100644 --- a/cmd/tailscaled/depaware.txt +++ b/cmd/tailscaled/depaware.txt @@ -212,7 +212,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de tailscale.com/logtail from tailscale.com/control/controlclient+ tailscale.com/logtail/backoff from tailscale.com/control/controlclient+ tailscale.com/logtail/filch from tailscale.com/logpolicy - 💣 tailscale.com/metrics from tailscale.com/derp+ + tailscale.com/metrics from tailscale.com/derp+ tailscale.com/net/dns from tailscale.com/ipn/ipnlocal+ tailscale.com/net/dns/publicdns from tailscale.com/net/dns/resolver+ tailscale.com/net/dns/resolvconffile from tailscale.com/net/dns+ @@ -275,6 +275,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de tailscale.com/util/cloudenv from tailscale.com/net/dns/resolver+ LW tailscale.com/util/cmpver from tailscale.com/net/dns+ 💣 tailscale.com/util/deephash from tailscale.com/ipn/ipnlocal+ + L 💣 tailscale.com/util/dirwalk from tailscale.com/metrics+ tailscale.com/util/dnsname from tailscale.com/hostinfo+ LW tailscale.com/util/endian from tailscale.com/net/dns+ tailscale.com/util/goroutines from tailscale.com/control/controlclient+ diff --git a/metrics/fds_linux.go b/metrics/fds_linux.go index 486e1a575..10930f737 100644 --- a/metrics/fds_linux.go +++ b/metrics/fds_linux.go @@ -5,105 +5,38 @@ package metrics import ( - "fmt" - "log" - "syscall" - "unsafe" + "io/fs" + "sync" - "golang.org/x/sys/unix" + "go4.org/mem" + "tailscale.com/util/dirwalk" ) -func currentFDs() int { - fd, err := openProcSelfFD() - if err != nil { - return 0 - } - defer syscall.Close(fd) - - count := 0 +// counter is a reusable counter for counting file descriptors. +type counter struct { + n int - const blockSize = 8 << 10 - buf := make([]byte, blockSize) // stack-allocated; doesn't escape - bufp := 0 // starting read position in buf - nbuf := 0 // end valid data in buf - dirent := &syscall.Dirent{} - for { - if bufp >= nbuf { - bufp = 0 - nbuf, err = readDirent(fd, buf) - if err != nil { - log.Printf("currentFDs: readDirent: %v", err) - return 0 - } - if nbuf <= 0 { - return count - } - } - consumed, name := parseDirEnt(dirent, buf[bufp:nbuf]) - bufp += consumed - if len(name) == 0 || string(name) == "." || string(name) == ".." { - continue - } - count++ - } + // cb is the (*counter).count method value. Creating it allocates, + // so we have to save it away and use a sync.Pool to keep currentFDs + // amortized alloc-free. + cb func(name mem.RO, de fs.DirEntry) error } -func direntNamlen(dirent *syscall.Dirent) int { - const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name)) - limit := dirent.Reclen - fixedHdr - const dirNameLen = 256 // sizeof syscall.Dirent.Name - if limit > dirNameLen { - limit = dirNameLen - } - for i := uint16(0); i < limit; i++ { - if dirent.Name[i] == 0 { - return int(i) - } - } - panic("failed to find terminating 0 byte in dirent") -} +var counterPool = &sync.Pool{New: func() any { + c := new(counter) + c.cb = c.count + return c +}} -func parseDirEnt(dirent *syscall.Dirent, buf []byte) (consumed int, name []byte) { - // golang.org/issue/37269 - copy(unsafe.Slice((*byte)(unsafe.Pointer(dirent)), unsafe.Sizeof(syscall.Dirent{})), buf) - if v := unsafe.Offsetof(dirent.Reclen) + unsafe.Sizeof(dirent.Reclen); uintptr(len(buf)) < v { - panic(fmt.Sprintf("buf size of %d smaller than dirent header size %d", len(buf), v)) - } - if len(buf) < int(dirent.Reclen) { - panic(fmt.Sprintf("buf size %d < record length %d", len(buf), dirent.Reclen)) - } - consumed = int(dirent.Reclen) - if dirent.Ino == 0 { // File absent in directory. - return - } - name = unsafe.Slice((*byte)(unsafe.Pointer(&dirent.Name[0])), direntNamlen(dirent)) - return +func (c *counter) count(name mem.RO, de fs.DirEntry) error { + c.n++ + return nil } -var procSelfFDName = []byte("/proc/self/fd\x00") - -func openProcSelfFD() (fd int, err error) { - var dirfd int = unix.AT_FDCWD - for { - r0, _, e1 := syscall.Syscall(unix.SYS_OPENAT, uintptr(dirfd), - uintptr(unsafe.Pointer(&procSelfFDName[0])), 0) - if e1 == 0 { - return int(r0), nil - } - if e1 == syscall.EINTR { - // Since https://golang.org/doc/go1.14#runtime we - // need to loop on EINTR on more places. - continue - } - return 0, syscall.Errno(e1) - } -} - -func readDirent(fd int, buf []byte) (n int, err error) { - for { - nbuf, err := syscall.ReadDirent(fd, buf) - if err != syscall.EINTR { - return nbuf, err - } - } +func currentFDs() int { + c := counterPool.Get().(*counter) + defer counterPool.Put(c) + c.n = 0 + dirwalk.WalkShallow(mem.S("/proc/self/fd"), c.cb) + return c.n } diff --git a/portlist/portlist_linux.go b/portlist/portlist_linux.go index 8d9176cd9..859270da8 100644 --- a/portlist/portlist_linux.go +++ b/portlist/portlist_linux.go @@ -10,11 +10,11 @@ import ( "errors" "fmt" "io" + "io/fs" "log" "os" "path/filepath" "runtime" - "strconv" "strings" "syscall" "time" @@ -22,6 +22,7 @@ import ( "go4.org/mem" "golang.org/x/sys/unix" + "tailscale.com/util/dirwalk" "tailscale.com/util/mak" ) @@ -32,7 +33,8 @@ func init() { } type linuxImpl struct { - procNetFiles []*os.File // seeked to start & reused between calls + procNetFiles []*os.File // seeked to start & reused between calls + readlinkPathBuf []byte known map[string]*portMeta // inode string => metadata br *bufio.Reader @@ -270,71 +272,59 @@ func (li *linuxImpl) findProcessNames(need map[string]*portMeta) error { } }() - var pathBuf []byte - - err := foreachPID(func(pid string) error { - fdPath := fmt.Sprintf("/proc/%s/fd", pid) + err := foreachPID(func(pid mem.RO) error { + var procBuf [128]byte + fdPath := mem.Append(procBuf[:0], mem.S("/proc/")) + fdPath = mem.Append(fdPath, pid) + fdPath = mem.Append(fdPath, mem.S("/fd")) // Android logs a bunch of audit violations in logcat // if we try to open things we don't have access // to. So on Android only, ask if we have permission // rather than just trying it to determine whether we // have permission. - if runtime.GOOS == "android" && syscall.Access(fdPath, unix.R_OK) != nil { - return nil - } - - fdDir, err := os.Open(fdPath) - if err != nil { - // Can't open fd list for this pid. Maybe - // don't have access. Ignore it. + if runtime.GOOS == "android" && syscall.Access(string(fdPath), unix.R_OK) != nil { return nil } - defer fdDir.Close() - targetBuf := make([]byte, 64) // plenty big for "socket:[165614651]" - for { - fds, err := fdDir.Readdirnames(100) - if err == io.EOF { + dirwalk.WalkShallow(mem.B(fdPath), func(fd mem.RO, de fs.DirEntry) error { + targetBuf := make([]byte, 64) // plenty big for "socket:[165614651]" + + linkPath := li.readlinkPathBuf[:0] + linkPath = fmt.Appendf(linkPath, "/proc/") + linkPath = mem.Append(linkPath, pid) + linkPath = append(linkPath, "/fd/"...) + linkPath = mem.Append(linkPath, fd) + linkPath = append(linkPath, 0) // terminating NUL + li.readlinkPathBuf = linkPath // to reuse its buffer next time + n, ok := readlink(linkPath, targetBuf) + if !ok { + // Not a symlink or no permission. + // Skip it. return nil } - if os.IsNotExist(err) { - // This can happen if the directory we're - // reading disappears during the run. No big - // deal. + + pe := need[string(targetBuf[:n])] // m[string([]byte)] avoids alloc + if pe == nil { return nil } + bs, err := os.ReadFile(fmt.Sprintf("/proc/%s/cmdline", pid.StringCopy())) if err != nil { - return fmt.Errorf("addProcesses.readDir: %w", err) + // Usually shouldn't happen. One possibility is + // the process has gone away, so let's skip it. + return nil } - for _, fd := range fds { - pathBuf = fmt.Appendf(pathBuf[:0], "/proc/%s/fd/%s\x00", pid, fd) - n, ok := readlink(pathBuf, targetBuf) - if !ok { - // Not a symlink or no permission. - // Skip it. - continue - } - - pe := need[string(targetBuf[:n])] // m[string([]byte)] avoids alloc - if pe != nil { - bs, err := os.ReadFile(fmt.Sprintf("/proc/%s/cmdline", pid)) - if err != nil { - // Usually shouldn't happen. One possibility is - // the process has gone away, so let's skip it. - continue - } - - argv := strings.Split(strings.TrimSuffix(string(bs), "\x00"), "\x00") - pe.port.Process = argvSubject(argv...) - pe.needsProcName = false - delete(need, string(targetBuf[:n])) - if len(need) == 0 { - return errDone - } - } + + argv := strings.Split(strings.TrimSuffix(string(bs), "\x00"), "\x00") + pe.port.Process = argvSubject(argv...) + pe.needsProcName = false + delete(need, string(targetBuf[:n])) + if len(need) == 0 { + return errDone } - } + return nil + }) + return nil }) if err == errDone { return nil @@ -342,40 +332,30 @@ func (li *linuxImpl) findProcessNames(need map[string]*portMeta) error { return err } -func foreachPID(fn func(pidStr string) error) error { - pdir, err := os.Open("/proc") - if err != nil { - return err - } - defer pdir.Close() - - for { - pids, err := pdir.Readdirnames(100) - if err == io.EOF { - return nil - } - if os.IsNotExist(err) { - // This can happen if the directory we're - // reading disappears during the run. No big - // deal. +func foreachPID(fn func(pidStr mem.RO) error) error { + err := dirwalk.WalkShallow(mem.S("/proc"), func(name mem.RO, de fs.DirEntry) error { + if !isNumeric(name) { return nil } - if err != nil { - return fmt.Errorf("foreachPID.readdir: %w", err) - } + return fn(name) + }) + if os.IsNotExist(err) { + // This can happen if the directory we're + // reading disappears during the run. No big + // deal. + return nil + } + return err +} - for _, pid := range pids { - _, err := strconv.ParseInt(pid, 10, 64) - if err != nil { - // not a pid, ignore it. - // /proc has lots of non-pid stuff in it. - continue - } - if err := fn(pid); err != nil { - return err - } +func isNumeric(s mem.RO) bool { + for i, n := 0, s.Len(); i < n; i++ { + b := s.At(i) + if b < '0' || b > '9' { + return false } } + return s.Len() > 0 } // fieldIndex returns the offset in line where the Nth field (0-based) begins, or -1 diff --git a/portlist/portlist_linux_test.go b/portlist/portlist_linux_test.go index a0b8e1dc5..a40ec097b 100644 --- a/portlist/portlist_linux_test.go +++ b/portlist/portlist_linux_test.go @@ -136,3 +136,16 @@ func BenchmarkParsePorts(b *testing.B) { } } } + +func BenchmarkFindProcessNames(b *testing.B) { + b.ReportAllocs() + li := &linuxImpl{} + need := map[string]*portMeta{ + "something-we'll-never-find": new(portMeta), + } + for i := 0; i < b.N; i++ { + if err := li.findProcessNames(need); err != nil { + b.Fatal(err) + } + } +} diff --git a/util/dirwalk/dirwalk.go b/util/dirwalk/dirwalk.go new file mode 100644 index 000000000..22e58fe1b --- /dev/null +++ b/util/dirwalk/dirwalk.go @@ -0,0 +1,54 @@ +// Copyright (c) 2022 Tailscale Inc & 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 dirwalk contains code to walk a directory. +package dirwalk + +import ( + "io" + "io/fs" + "os" + + "go4.org/mem" +) + +var osWalkShallow func(name mem.RO, fn WalkFunc) error + +// WalkFunc is the callback type used with WalkShallow. +// +// The name and de are only valid for the duration of func's call +// and should not be retained. +type WalkFunc func(name mem.RO, de fs.DirEntry) error + +// WalkShallow reads the entries in the named directory and calls fn for each. +// It does not recurse into subdirectories. +// +// If fn returns an error, iteration stops and WalkShallow returns that value. +// +// On Linux, WalkShallow does not allocate, so long as certain methods on the +// WalkFunc's DirEntry are not called which necessarily allocate. +func WalkShallow(dirName mem.RO, fn WalkFunc) error { + if f := osWalkShallow; f != nil { + return f(dirName, fn) + } + of, err := os.Open(dirName.StringCopy()) + if err != nil { + return err + } + defer of.Close() + for { + fis, err := of.ReadDir(100) + for _, de := range fis { + if err := fn(mem.S(de.Name()), de); err != nil { + return err + } + } + if err != nil { + if err == io.EOF { + return nil + } + return err + } + } +} diff --git a/util/dirwalk/dirwalk_linux.go b/util/dirwalk/dirwalk_linux.go new file mode 100644 index 000000000..7abcc9b34 --- /dev/null +++ b/util/dirwalk/dirwalk_linux.go @@ -0,0 +1,168 @@ +// Copyright (c) 2022 Tailscale Inc & 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 dirwalk + +import ( + "fmt" + "io/fs" + "os" + "path/filepath" + "sync" + "syscall" + "unsafe" + + "go4.org/mem" + "golang.org/x/sys/unix" +) + +func init() { + osWalkShallow = linuxWalkShallow +} + +var dirEntPool = &sync.Pool{New: func() any { return new(linuxDirEnt) }} + +func linuxWalkShallow(dirName mem.RO, fn WalkFunc) error { + const blockSize = 8 << 10 + buf := make([]byte, blockSize) // stack-allocated; doesn't escape + + nameb := mem.Append(buf[:0], dirName) + nameb = append(nameb, 0) + + fd, err := sysOpen(nameb) + if err != nil { + return err + } + defer syscall.Close(fd) + + bufp := 0 // starting read position in buf + nbuf := 0 // end valid data in buf + + de := dirEntPool.Get().(*linuxDirEnt) + defer de.cleanAndPutInPool() + de.root = dirName + + for { + if bufp >= nbuf { + bufp = 0 + nbuf, err = readDirent(fd, buf) + if err != nil { + return err + } + if nbuf <= 0 { + return nil + } + } + consumed, name := parseDirEnt(&de.d, buf[bufp:nbuf]) + bufp += consumed + if len(name) == 0 || string(name) == "." || string(name) == ".." { + continue + } + de.name = mem.B(name) + if err := fn(de.name, de); err != nil { + return err + } + } +} + +type linuxDirEnt struct { + root mem.RO + d syscall.Dirent + name mem.RO +} + +func (de *linuxDirEnt) cleanAndPutInPool() { + de.root = mem.RO{} + de.name = mem.RO{} + dirEntPool.Put(de) +} + +func (de *linuxDirEnt) Name() string { return de.name.StringCopy() } +func (de *linuxDirEnt) Info() (fs.FileInfo, error) { + return os.Lstat(filepath.Join(de.root.StringCopy(), de.name.StringCopy())) +} +func (de *linuxDirEnt) IsDir() bool { + return de.d.Type == syscall.DT_DIR +} +func (de *linuxDirEnt) Type() fs.FileMode { + switch de.d.Type { + case syscall.DT_BLK: + return fs.ModeDevice // shrug + case syscall.DT_CHR: + return fs.ModeCharDevice + case syscall.DT_DIR: + return fs.ModeDir + case syscall.DT_FIFO: + return fs.ModeNamedPipe + case syscall.DT_LNK: + return fs.ModeSymlink + case syscall.DT_REG: + return 0 + case syscall.DT_SOCK: + return fs.ModeSocket + default: + return fs.ModeIrregular // shrug + } +} + +func direntNamlen(dirent *syscall.Dirent) int { + const fixedHdr = uint16(unsafe.Offsetof(syscall.Dirent{}.Name)) + limit := dirent.Reclen - fixedHdr + const dirNameLen = 256 // sizeof syscall.Dirent.Name + if limit > dirNameLen { + limit = dirNameLen + } + for i := uint16(0); i < limit; i++ { + if dirent.Name[i] == 0 { + return int(i) + } + } + panic("failed to find terminating 0 byte in dirent") +} + +func parseDirEnt(dirent *syscall.Dirent, buf []byte) (consumed int, name []byte) { + // golang.org/issue/37269 + copy(unsafe.Slice((*byte)(unsafe.Pointer(dirent)), unsafe.Sizeof(syscall.Dirent{})), buf) + if v := unsafe.Offsetof(dirent.Reclen) + unsafe.Sizeof(dirent.Reclen); uintptr(len(buf)) < v { + panic(fmt.Sprintf("buf size of %d smaller than dirent header size %d", len(buf), v)) + } + if len(buf) < int(dirent.Reclen) { + panic(fmt.Sprintf("buf size %d < record length %d", len(buf), dirent.Reclen)) + } + consumed = int(dirent.Reclen) + if dirent.Ino == 0 { // File absent in directory. + return + } + name = unsafe.Slice((*byte)(unsafe.Pointer(&dirent.Name[0])), direntNamlen(dirent)) + return +} + +func sysOpen(name []byte) (fd int, err error) { + if len(name) == 0 || name[len(name)-1] != 0 { + return 0, syscall.EINVAL + } + var dirfd int = unix.AT_FDCWD + for { + r0, _, e1 := syscall.Syscall(unix.SYS_OPENAT, uintptr(dirfd), + uintptr(unsafe.Pointer(&name[0])), 0) + if e1 == 0 { + return int(r0), nil + } + if e1 == syscall.EINTR { + // Since https://golang.org/doc/go1.14#runtime we + // need to loop on EINTR on more places. + continue + } + return 0, syscall.Errno(e1) + } +} + +func readDirent(fd int, buf []byte) (n int, err error) { + for { + nbuf, err := syscall.ReadDirent(fd, buf) + if err != syscall.EINTR { + return nbuf, err + } + } +} diff --git a/util/dirwalk/dirwalk_test.go b/util/dirwalk/dirwalk_test.go new file mode 100644 index 000000000..ed6947ca9 --- /dev/null +++ b/util/dirwalk/dirwalk_test.go @@ -0,0 +1,93 @@ +// Copyright (c) 2022 Tailscale Inc & 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 dirwalk + +import ( + "fmt" + "os" + "path/filepath" + "reflect" + "runtime" + "sort" + "testing" + + "go4.org/mem" +) + +func TestWalkShallowOSSpecific(t *testing.T) { + if osWalkShallow == nil { + t.Skip("no OS-specific implementation") + } + testWalkShallow(t, false) +} + +func TestWalkShallowPortable(t *testing.T) { + testWalkShallow(t, true) +} + +func testWalkShallow(t *testing.T, portable bool) { + if portable { + old := osWalkShallow + defer func() { osWalkShallow = old }() + osWalkShallow = nil + } + d := t.TempDir() + + t.Run("basics", func(t *testing.T) { + if err := os.WriteFile(filepath.Join(d, "foo"), []byte("1"), 0600); err != nil { + t.Fatal(err) + } + if err := os.WriteFile(filepath.Join(d, "bar"), []byte("22"), 0400); err != nil { + t.Fatal(err) + } + if err := os.Mkdir(filepath.Join(d, "baz"), 0777); err != nil { + t.Fatal(err) + } + + var got []string + if err := WalkShallow(mem.S(d), func(name mem.RO, de os.DirEntry) error { + var size int64 + if fi, err := de.Info(); err != nil { + t.Errorf("Info stat error on %q: %v", de.Name(), err) + } else if !fi.IsDir() { + size = fi.Size() + } + got = append(got, fmt.Sprintf("%q %q dir=%v type=%d size=%v", name.StringCopy(), de.Name(), de.IsDir(), de.Type(), size)) + return nil + }); err != nil { + t.Fatal(err) + } + sort.Strings(got) + want := []string{ + `"bar" "bar" dir=false type=0 size=2`, + `"baz" "baz" dir=true type=2147483648 size=0`, + `"foo" "foo" dir=false type=0 size=1`, + } + if !reflect.DeepEqual(got, want) { + t.Errorf("mismatch:\n got %#q\nwant %#q", got, want) + } + }) + + t.Run("err_not_exist", func(t *testing.T) { + err := WalkShallow(mem.S(filepath.Join(d, "not_exist")), func(name mem.RO, de os.DirEntry) error { + return nil + }) + if !os.IsNotExist(err) { + t.Errorf("unexpected error: %v", err) + } + }) + + t.Run("allocs", func(t *testing.T) { + allocs := int(testing.AllocsPerRun(1000, func() { + if err := WalkShallow(mem.S(d), func(name mem.RO, de os.DirEntry) error { return nil }); err != nil { + t.Fatal(err) + } + })) + t.Logf("allocs = %v", allocs) + if !portable && runtime.GOOS == "linux" && allocs != 0 { + t.Errorf("unexpected allocs: got %v, want 0", allocs) + } + }) +}