os: don't try to make the directory FD non-blocking in os.ReadDir

This will fail because epoll_ctl() fails on directory FDs, so we
end up issuing unnecessary syscalls. My test program that calls
filepath.WalkDir on a large directory tree runs 1.23 ± 0.04 times
faster than with the original implementation.

Change-Id: Ie33d798c48057a7b2d0bacac80fcdde5b5a8bb1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/570877
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

diff --git a/src/os/dir.go b/src/os/dir.go
index 9124de29e8cdf5704149b3a1d4fdc42960564930..dcc18e18144783d712028e7776832e851f8d5179 100644 (file)
--- a/src/os/dir.go
+++ b/src/os/dir.go
@@ -115,7 +115,7 @@ var testingForceReadDirLstat bool
 // ReadDir returns the entries it was able to read before the error,
 // along with the error.
 func ReadDir(name string) ([]DirEntry, error) {
-       f, err := Open(name)
+       f, err := openDir(name)
        if err != nil {
                return nil, err
        }

diff --git a/src/os/file.go b/src/os/file.go
index c0c972bbd7bc5798a7853e1064d0a907130d0665..fae7bf1039df5fe733a891441d024eb0fd27d39e 100644 (file)
--- a/src/os/file.go
+++ b/src/os/file.go
@@ -380,6 +380,14 @@ func OpenFile(name string, flag int, perm FileMode) (*File, error) {
        return f, nil
 }
 
+// openDir opens a file which is assumed to be a directory. As such, it skips
+// the syscalls that make the file descriptor non-blocking as these take time
+// and will fail on file descriptors for directories.
+func openDir(name string) (*File, error) {
+       testlog.Open(name)
+       return openDirNolog(name)
+}
+
 // lstat is overridden in tests.
 var lstat = Lstat
 

diff --git a/src/os/file_plan9.go b/src/os/file_plan9.go
index 69a24316e6a120db2352705b4c9152a88050383d..477674b80a95c81ce7bcf7335462822eab3b55ef 100644 (file)
--- a/src/os/file_plan9.go
+++ b/src/os/file_plan9.go
@@ -139,6 +139,10 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
        return NewFile(uintptr(fd), name), nil
 }
 
+func openDirNolog(name string) (*File, error) {
+       return openFileNolog(name, O_RDONLY, 0)
+}
+
 // Close closes the File, rendering it unusable for I/O.
 // On files that support SetDeadline, any pending I/O operations will
 // be canceled and return immediately with an ErrClosed error.

diff --git a/src/os/file_unix.go b/src/os/file_unix.go
index 6597186486c6479a4341c4d33d988cafdebcfccc..924ec25ed911739b2753785c85f96aa54e2ee571 100644 (file)
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -157,7 +157,7 @@ const (
        kindNonBlock
        // kindNoPoll means that we should not put the descriptor into
        // non-blocking mode, because we know it is not a pipe or FIFO.
-       // Used by openFdAt for directories.
+       // Used by openFdAt and openDirNolog for directories.
        kindNoPoll
 )
 
@@ -256,7 +256,7 @@ func epipecheck(file *File, e error) {
 const DevNull = "/dev/null"
 
 // openFileNolog is the Unix implementation of OpenFile.
-// Changes here should be reflected in openFdAt, if relevant.
+// Changes here should be reflected in openFdAt and openDirNolog, if relevant.
 func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
        setSticky := false
        if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
@@ -303,6 +303,32 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
        return f, nil
 }
 
+func openDirNolog(name string) (*File, error) {
+       var r int
+       var s poll.SysFile
+       for {
+               var e error
+               r, s, e = open(name, O_RDONLY|syscall.O_CLOEXEC, 0)
+               if e == nil {
+                       break
+               }
+
+               if e == syscall.EINTR {
+                       continue
+               }
+
+               return nil, &PathError{Op: "open", Path: name, Err: e}
+       }
+
+       if !supportsCloseOnExec {
+               syscall.CloseOnExec(r)
+       }
+
+       f := newFile(r, name, kindNoPoll)
+       f.pfd.SysFile = s
+       return f, nil
+}
+
 func (file *file) close() error {
        if file == nil {
                return syscall.EINVAL

diff --git a/src/os/file_windows.go b/src/os/file_windows.go
index fcdb5f2e8f8cc8b7c455f13ddf0e668957073327..a304a5e4a7752ee098a42540b1a810585b5b19ee 100644 (file)
--- a/src/os/file_windows.go
+++ b/src/os/file_windows.go
@@ -119,6 +119,10 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
        return newFile(r, name, "file"), nil
 }
 
+func openDirNolog(name string) (*File, error) {
+       return openFileNolog(name, O_RDONLY, 0)
+}
+
 func (file *file) close() error {
        if file == nil {
                return syscall.EINVAL