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net/dns: print systemd-resolved ResolvConfMode

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The ResolvConfMode property is documented to return how systemd-resolved
is currently managing /etc/resolv.conf. Include that information in the
debug line, when available, to assist in debugging DNS issues.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I1ae3a257df1d318d0193a8c7f135c458ec45093e
This commit is contained in:
Andrew Dunham
2022-10-14 20:25:22 +02:00
parent 223126fe5b
commit e966f024b0
2 changed files with 100 additions and 15 deletions
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48
net/dns/manager_linux.go
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@@ -31,6 +31,7 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
env := newOSConfigEnv{
fs: directFS{},
dbusPing: dbusPing,
dbusReadString: dbusReadString,
nmIsUsingResolved: nmIsUsingResolved,
nmVersionBetween: nmVersionBetween,
resolvconfStyle: resolvconfStyle,
@@ -60,6 +61,7 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
type newOSConfigEnv struct {
fs wholeFileFS
dbusPing func(string, string) error
dbusReadString func(string, string, string, string) (string, error)
nmIsUsingResolved func() error
nmVersionBetween func(v1, v2 string) (safe bool, err error)
resolvconfStyle func() string
@@ -78,6 +80,25 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
logf("dns: %v", debug)
}()
// In all cases that we detect systemd-resolved, try asking it what it
// thinks the current resolv.conf mode is so we can add it to our logs.
defer func() {
if ret != "systemd-resolved" {
return
}
// Try to ask systemd-resolved what it thinks the current
// status of resolv.conf is. This is documented at:
// https://www.freedesktop.org/software/systemd/man/org.freedesktop.resolve1.html
mode, err := env.dbusReadString("org.freedesktop.resolve1", "/org/freedesktop/resolve1", "org.freedesktop.resolve1.Manager", "ResolvConfMode")
if err != nil {
logf("dns: ResolvConfMode error: %v", err)
dbg("resolv-conf-mode", "error")
} else {
dbg("resolv-conf-mode", mode)
}
}()
// Before we read /etc/resolv.conf (which might be in a broken
// or symlink-dangling state), try to ping the D-Bus service
// for systemd-resolved. If it's active on the machine, this
@@ -102,6 +123,7 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
switch resolvOwner(bs) {
case "systemd-resolved":
dbg("rc", "resolved")
// Some systems, for reasons known only to them, have a
// resolv.conf that has the word "systemd-resolved" in its
// header, but doesn't actually point to resolved. We mustn't
@@ -327,3 +349,29 @@ func dbusPing(name, objectPath string) error {
call := obj.CallWithContext(ctx, "org.freedesktop.DBus.Peer.Ping", 0)
return call.Err
}
// dbusReadString reads a string property from the provided name and object
// path. property must be in "interface.member" notation.
func dbusReadString(name, objectPath, iface, member string) (string, error) {
conn, err := dbus.SystemBus()
if err != nil {
// DBus probably not running.
return "", err
}
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
defer cancel()
obj := conn.Object(name, dbus.ObjectPath(objectPath))
var result dbus.Variant
err = obj.CallWithContext(ctx, "org.freedesktop.DBus.Properties.Get", 0, iface, member).Store(&result)
if err != nil {
return "", err
}
if s, ok := result.Value().(string); ok {
return s, nil
}
return result.String(), nil
}