syscallcompat: implement Getdents()

The Readdir function provided by os is inherently slow because
it calls Lstat on all files.

Getdents gives us all the information we need, but does not have
a proper wrapper in the stdlib.

Implement the "Getdents()" wrapper function that calls
syscall.Getdents() and parses the returned byte blob to a
fuse.DirEntry slice.

1 files changed, 77 insertions, 0 deletions

diff --git a/internal/syscallcompat/getdents_test.go b/internal/syscallcompat/getdents_test.go
new file mode 100644
index 0000000..f0b1e60
--- /dev/null
+++ b/internal/syscallcompat/getdents_test.go
@@ -0,0 +1,77 @@
+// +build linux
+
+package syscallcompat
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+	"syscall"
+	"testing"
+
+	"github.com/hanwen/go-fuse/fuse"
+)
+
+func TestGetdents(t *testing.T) {
+	// Fill a directory with filenames of length 1 ... 255
+	testDir, err := ioutil.TempDir("", "TestGetdents")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 1; i <= syscall.NAME_MAX; i++ {
+		n := strings.Repeat("x", i)
+		err = ioutil.WriteFile(testDir+"/"+n, nil, 0600)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	// "/", "/dev" and "/proc" are good test cases because they contain many
+	// different file types (block and char devices, symlinks, mountpoints)
+	dirs := []string{testDir, "/", "/dev", "/proc"}
+	for _, dir := range dirs {
+		// Read directory using stdlib Readdir()
+		fd, err := os.Open(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		readdirEntries, err := fd.Readdir(0)
+		if err != nil {
+			t.Fatal(err)
+		}
+		fd.Close()
+		readdirMap := make(map[string]*syscall.Stat_t)
+		for _, v := range readdirEntries {
+			readdirMap[v.Name()] = fuse.ToStatT(v)
+		}
+		// Read using our Getdents()
+		getdentsEntries, err := Getdents(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		getdentsMap := make(map[string]fuse.DirEntry)
+		for _, v := range getdentsEntries {
+			getdentsMap[v.Name] = v
+		}
+		// Compare results
+		if len(getdentsEntries) != len(readdirEntries) {
+			t.Fatalf("len(getdentsEntries)=%d, len(readdirEntries)=%d",
+				len(getdentsEntries), len(readdirEntries))
+		}
+		for name := range readdirMap {
+			g := getdentsMap[name]
+			r := readdirMap[name]
+			rTyp := r.Mode & syscall.S_IFMT
+			if g.Mode != rTyp {
+				t.Errorf("%q: g.Mode=%#o, r.Mode=%#o", name, g.Mode, rTyp)
+			}
+			if g.Ino != r.Ino {
+				// The inode number of a directory that is reported by stat
+				// and getdents is different when it is a mountpoint. Only
+				// throw an error when we are NOT looking at a directory.
+				if g.Mode != syscall.S_IFDIR {
+					t.Errorf("%s: g.Ino=%d, r.Ino=%d", name, g.Ino, r.Ino)
+				}
+			}
+		}
+	}
+}