corecfg: add "system.timezone" setting to the system settings

This commit adds support for setting the timezone via the snap
configuration system. This allows image customizations in UC20
that used to be done via direct manipulation of the "writable"
partition in UC16/UC18.

The image customization part will be fine as is but for the runtime
setting we also need to fix LP: #1650688

overlord/configstate/configcore/handlers.go

@@ -85,6 +85,9 @@ func init() {
 	// journal.persistent
 	addFSOnlyHandler(validateJournalSettings, handleJournalConfiguration, coreOnly)
 
+	// system.timezone
+	addFSOnlyHandler(validateTimezoneSettings, handleTimezoneConfiguration, coreOnly)
+
 	sysconfig.ApplyFilesystemOnlyDefaultsImpl = func(rootDir string, defaults map[string]interface{}, options *sysconfig.FilesystemOnlyApplyOptions) error {
 		return filesystemOnlyApply(rootDir, plainCoreConfig(defaults), options)
 	}

overlord/configstate/configcore/timezone.go

@@ -0,0 +1,86 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2020 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 configcore
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+
+	"github.com/snapcore/snapd/osutil"
+	"github.com/snapcore/snapd/overlord/configstate/config"
+)
+
+func init() {
+	// add supported configuration of this module
+	supportedConfigurations["core.system.timezone"] = true
+}
+
+var validTimezone = regexp.MustCompile(`^[a-zA-Z0-9+-]+(/[a-zA-Z0-9+-]+)?$`).MatchString
+
+func validateTimezoneSettings(tr config.ConfGetter) error {
+	timezone, err := coreCfg(tr, "system.timezone")
+	if err != nil {
+		return err
+	}
+	if timezone == "" {
+		return nil
+	}
+	if !validTimezone(timezone) {
+		return fmt.Errorf("cannot set timezone %q: name not valid", timezone)
+	}
+
+	return nil
+}
+
+func handleTimezoneConfiguration(tr config.ConfGetter, opts *fsOnlyContext) error {
+	output, err := coreCfg(tr, "system.timezone")
+	if err != nil {
+		return nil
+	}
+	// nothing to do
+	if output == "" {
+		return nil
+	}
+	// runtime system
+	if opts == nil {
+		output, err := exec.Command("timedatectl", "set-timezone", output).CombinedOutput()
+		if err != nil {
+			return fmt.Errorf("cannot set timezone: %v", osutil.OutputErr(output, err))
+		}
+	} else {
+		// important to use /etc/writable/
+		localtimePath := filepath.Join(opts.RootDir, "/etc/writable/localtime")
+		if err := os.MkdirAll(filepath.Dir(localtimePath), 0755); err != nil {
+			return err
+		}
+		if err := os.Symlink(filepath.Join("/usr/share/zoneinfo", output), localtimePath); err != nil {
+			return err
+		}
+		timezonePath := filepath.Join(opts.RootDir, "/etc/writable/timezone")
+		if err := osutil.AtomicWriteFile(timezonePath, []byte(output+"\n"), 0644, 0); err != nil {
+			return fmt.Errorf("cannot write timezone: %v", err)
+		}
+	}
+
+	return nil
+}

overlord/configstate/configcore/timezone_test.go

@@ -0,0 +1,101 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2020 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 configcore_test
+
+import (
+	"os"
+	"path/filepath"
+
+	. "gopkg.in/check.v1"
+
+	"github.com/snapcore/snapd/dirs"
+	"github.com/snapcore/snapd/overlord/configstate/configcore"
+	"github.com/snapcore/snapd/release"
+	"github.com/snapcore/snapd/testutil"
+)
+
+type timezoneSuite struct {
+	configcoreSuite
+}
+
+var _ = Suite(&timezoneSuite{})
+
+func (s *timezoneSuite) SetUpTest(c *C) {
+	s.configcoreSuite.SetUpTest(c)
+
+	err := os.MkdirAll(filepath.Join(dirs.GlobalRootDir, "/etc/"), 0755)
+	c.Assert(err, IsNil)
+}
+
+func (s *timezoneSuite) TestConfigureTimezoneInvalid(c *C) {
+	invalidTimezones := []string{
+		"no-#", "no-ä", "no/double/slash",
+	}
+
+	for _, tz := range invalidTimezones {
+		err := configcore.Run(&mockConf{
+			state: s.state,
+			conf: map[string]interface{}{
+				"system.timezone": tz,
+			},
+		})
+		c.Assert(err, ErrorMatches, `cannot set timezone.*`)
+	}
+}
+
+func (s *timezoneSuite) TestConfigureTimezoneIntegration(c *C) {
+	restore := release.MockOnClassic(false)
+	defer restore()
+
+	mockedTimedatectl := testutil.MockCommand(c, "timedatectl", "")
+	defer mockedTimedatectl.Restore()
+
+	validTimezones := []string{
+		"UTC", "Europe/Malta", "US/Indiana-Starke",
+		"Etc/GMT+1", "CST6CDT", "GMT0", "GMT-0", "PST8PDT",
+	}
+
+	for _, tz := range validTimezones {
+		err := configcore.Run(&mockConf{
+			state: s.state,
+			conf: map[string]interface{}{
+				"system.timezone": tz,
+			},
+		})
+		c.Assert(err, IsNil)
+		c.Check(mockedTimedatectl.Calls(), DeepEquals, [][]string{
+			{"timedatectl", "set-timezone", tz},
+		})
+		mockedTimedatectl.ForgetCalls()
+	}
+}
+
+func (s *timezoneSuite) TestFilesystemOnlyApply(c *C) {
+	conf := configcore.PlainCoreConfig(map[string]interface{}{
+		"system.timezone": "Europe/Berlin",
+	})
+	tmpDir := c.MkDir()
+	c.Assert(configcore.FilesystemOnlyApply(tmpDir, conf, nil), IsNil)
+
+	c.Check(filepath.Join(tmpDir, "/etc/writable/timezone"), testutil.FileEquals, "Europe/Berlin\n")
+	p, err := os.Readlink(filepath.Join(tmpDir, "/etc/writable/localtime"))
+	c.Assert(err, IsNil)
+	c.Check(p, Equals, "/usr/share/zoneinfo/Europe/Berlin")
+}

tests/core/snap-set-core-config/task.yaml

@@ -29,7 +29,10 @@ restore: |
         systemctl enable rsyslog.service
         systemctl start rsyslog.service
     fi
-
+    if [ -e current-timezone ]; then
+        timedatectl set-timezone "$(cat current-timezone)"
+    fi
+ 
     rm -f /etc/systemd/login.conf.d/00-snap-core.conf
 
 execute: |
@@ -134,3 +137,9 @@ execute: |
     snap unset system system.kernel.printk.console-loglevel
     not test -e /etc/sysctl.d/99-snapd.conf
     sysctl -n kernel.printk|MATCH "^4\s+"
+
+    echo "setting the timezone works"
+    cat /etc/timezone > current-timezone
+    snap set system system.timezone=Europe/Malta
+    MATCH "Europe/Malta" /etc/timezone
+    test "$(readlink -f /etc/localtime)" = "/usr/share/zoneinfo/Europe/Malta"

tests/nested/manual/core-early-config/defaults.yaml

@@ -3,3 +3,5 @@ defaults:
     service:
       rsyslog:
         disable: true
+    system:
+      timezone: Europe/Malta

tests/nested/manual/core-early-config/task.yaml

@@ -61,3 +61,7 @@ execute: |
     # early config is witnessed by install hook of the pc gadget
     execute_remote "cat /var/snap/pc/common/debug.txt" | MATCH "/dev/null"
     execute_remote "test -L /etc/systemd/system/rsyslog.service"
+
+    # timezone is set
+    execute_remote "cat /etc/timezone" | MATCH "Europe/Malta"
+    execute_remote "readlink -f /etc/localtime" | MATCH "Europe/Malta"