sysfs: consolidates errno coersion and maps EAGAIN and EINTR (#1113)

Signed-off-by: Adrian Cole <adrian@tetrate.io>
Co-authored-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/sysfs/dirfs_test.go

@@ -71,6 +71,11 @@ func TestDirFS_MkDir(t *testing.T) {
 		err := testFS.Mkdir(name, fs.ModeDir)
 		require.Equal(t, syscall.EEXIST, err)
 	})
+	t.Run("try creating on file", func(t *testing.T) {
+		filePath := pathutil.Join("non-existing-dir", "foo.txt")
+		err := testFS.Mkdir(filePath, fs.ModeDir)
+		require.Equal(t, syscall.ENOENT, err)
+	})
 }
 
 func TestDirFS_Rename(t *testing.T) {
@@ -577,8 +582,8 @@ func TestDirFS_Readlink(t *testing.T) {
 
 	buf := make([]byte, 200)
 	for _, tl := range testLinks {
-		err := os.Symlink(pathutil.Join(tl.old), pathutil.Join(tmpDir, tl.dst))
-		require.NoError(t, err)
+		err := testFS.Symlink(tl.old, tl.dst) // not os.Symlink for windows compat
+		require.NoError(t, err, "%v", tl)
 
 		n, err := testFS.Readlink(tl.dst, buf)
 		require.NoError(t, err)