osutil, interfaces/apparmor: add and use of osutil.UnlinkMany

This adds `osutil.UnlinkMany`, which is mostly just a convenience
function to remove multiple files form a single directory. It also
uses it from interfaces/apparmor.

interfaces/apparmor/apparmor.go

@@ -30,7 +30,6 @@ import (
 	"io"
 	"os"
 	"os/exec"
-	"path/filepath"
 	"strings"
 
 	"github.com/snapcore/snapd/osutil"
@@ -88,12 +87,8 @@ func unloadProfiles(names []string, cacheDir string) error {
 	if err != nil {
 		return fmt.Errorf("cannot unload apparmor profile: %s\napparmor_parser output:\n%s", err, string(output))
 	}
-	for _, name := range names {
-		err = os.Remove(filepath.Join(cacheDir, name))
-		// It is not an error if the cache file wasn't there to remove.
-		if err != nil && !os.IsNotExist(err) {
-			return fmt.Errorf("cannot remove apparmor profile cache: %s", err)
-		}
+	if err := osutil.UnlinkMany(cacheDir, names); err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("cannot remove apparmor profile cache: %s", err)
 	}
 	return nil
 }

osutil/unlink.go

@@ -0,0 +1,59 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2018 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package osutil
+
+import (
+	"os"
+	"syscall"
+)
+
+// UnlinkMany removes multiple files from a single directory.
+//
+// If dirname is not a directory, this will fail.
+//
+// This will abort at the first removal error (but ENOENT is ignored).
+//
+// Filenames must refer to files. They don't necessarily have to be
+// relative paths to the given dirname, but if they aren't why are you
+// using this function?
+//
+// Errors are *os.PathError, for convenience
+func UnlinkMany(dirname string, filenames []string) error {
+	dirfd, err := syscall.Open(dirname, syscall.O_RDONLY|syscall.O_CLOEXEC|syscall.O_DIRECTORY|0x200000, 0)
+	if err != nil {
+		return &os.PathError{
+			Op:   "open",
+			Path: dirname,
+			Err:  err,
+		}
+	}
+	defer syscall.Close(dirfd)
+
+	for _, filename := range filenames {
+		if err = sysUnlinkat(dirfd, filename); err != nil && err != syscall.ENOENT {
+			return &os.PathError{
+				Op:   "remove",
+				Path: filename,
+				Err:  err,
+			}
+		}
+	}
+	return nil
+}

osutil/unlink_darwin.go

@@ -0,0 +1,29 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2018 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package osutil
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// sys/unix _does_ expose flags, so we need to wrap it
+func sysUnlinkat(dirfd int, path string) error {
+	return unix.Unlinkat(dirfd, path, 0)
+}

osutil/unlink_linux.go

@@ -0,0 +1,27 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2018 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package osutil
+
+import (
+	"syscall"
+)
+
+// syscall.Unlinkat calls unlinkat(2) _without_ AT_REMOVEDIR, which is exactly what we want
+var sysUnlinkat = syscall.Unlinkat

osutil/unlink_test.go

@@ -0,0 +1,100 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2018 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package osutil_test
+
+import (
+	"os"
+	"path/filepath"
+	"sort"
+
+	"gopkg.in/check.v1"
+
+	"github.com/snapcore/snapd/osutil"
+)
+
+type unlinkSuite struct {
+	d string
+}
+
+var _ = check.Suite(&unlinkSuite{})
+
+func (s *unlinkSuite) checkDirnames(c *check.C, names []string) {
+	dir, err := os.Open(s.d)
+	c.Assert(err, check.IsNil)
+	defer dir.Close()
+	found, err := dir.Readdirnames(-1)
+	c.Assert(err, check.IsNil)
+	sort.Strings(names)
+	sort.Strings(found)
+	c.Check(found, check.DeepEquals, names)
+}
+
+func (s *unlinkSuite) SetUpTest(c *check.C) {
+	s.d = c.MkDir()
+	s.mkFixture(c)
+}
+
+func (s *unlinkSuite) mkFixture(c *check.C) {
+	for _, fname := range []string{"foo", "bar", "baz", "quux"} {
+		f, err := os.Create(filepath.Join(s.d, fname))
+		if err == nil {
+			f.Close()
+		} else if !os.IsExist(err) {
+			c.Fatal(err)
+		}
+	}
+	if err := os.Mkdir(filepath.Join(s.d, "dir"), 0700); err != nil && !os.IsExist(err) {
+		c.Fatal(err)
+	}
+}
+
+func (s *unlinkSuite) TestUnlinkMany(c *check.C) {
+	c.Assert(osutil.UnlinkMany(s.d, []string{"bar", "does-not-exist", "baz"}), check.IsNil)
+
+	s.checkDirnames(c, []string{"foo", "quux", "dir"})
+}
+
+func (s *unlinkSuite) TestUnlinkManyFails(c *check.C) {
+	type T struct {
+		dirname   string
+		filenames []string
+		expected  string
+	}
+	tests := []T{
+		{
+			dirname:   filepath.Join(s.d, "does-not-exist"),
+			filenames: []string{"bar", "baz"},
+			expected:  `open /tmp/.*/does-not-exist: no such file or directory`,
+		}, {
+			dirname:   filepath.Join(s.d, "foo"),
+			filenames: []string{"bar", "baz"},
+			expected:  `open /tmp/.*/foo: not a directory`,
+		}, {
+			dirname:   s.d,
+			filenames: []string{"bar", "dir", "baz"},
+			expected:  `remove dir: is a directory`,
+		},
+	}
+
+	for i, test := range tests {
+		c.Check(osutil.UnlinkMany(test.dirname, test.filenames), check.ErrorMatches, test.expected, check.Commentf("%d", i))
+		s.mkFixture(c)
+	}
+}