networkd: various fixes for the IPv6 privacy extensions support

- Make sure that the IPv6PrivacyExtensions=yes results in
  prefer-temporary, not prefer-public.

- Introduce special enum value "kernel" to leave setting unset, similar
  how we have it for the IP forwarding settings.

- Bring the enum values in sync with the the strings we parse for them,
  to the level this makes sense (specifically, rename "disabled" to
  "no", and "prefer-temporary" to "yes").

- Make sure we really set the value to to "no" by default, the way it is
  already documented in the man page.

- Fix whitespace error.

- Make sure link_ipv6_privacy_extensions() actually returns the correct
  enum type, rather than implicitly casting it to "bool".

- properly size formatting buffer for ipv6 sysctl value

- Don't complain if /proc/sys isn't writable

- Document that the enum follows the kernel's own values (0 = off, 1 =
  prefer-public, 2 = prefer-temporary)

- Drop redundant negating of error code passed to log_syntax()

- Manpage fixes

This fixes a number of issues from PR #417

1 files changed, 13 insertions, 9 deletions

diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index eb07e12773..5607cf470e 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -116,15 +116,12 @@ static bool link_ipv6_forward_enabled(Link *link) {
         return link->network->ip_forward & ADDRESS_FAMILY_IPV6;
 }
 
-static bool link_ipv6_privacy_extensions_enabled(Link *link) {
+static IPv6PrivacyExtensions link_ipv6_privacy_extensions(Link *link) {
         if (link->flags & IFF_LOOPBACK)
-                return false;
+                return _IPV6_PRIVACY_EXTENSIONS_INVALID;
 
         if (!link->network)
-                return false;
-
-        if (link->network->ipv6_privacy_extensions == _IPV6_PRIVACY_EXTENSIONS_INVALID)
-                return false;
+                return _IPV6_PRIVACY_EXTENSIONS_INVALID;
 
         return link->network->ipv6_privacy_extensions;
 }
@@ -1540,7 +1537,8 @@ static int link_set_ipv6_forward(Link *link) {
 }
 
 static int link_set_ipv6_privacy_extensions(Link *link) {
-        char buf[2 * DECIMAL_STR_MAX(unsigned) + 1];
+        char buf[DECIMAL_STR_MAX(unsigned) + 1];
+        IPv6PrivacyExtensions s;
         const char *p = NULL;
         int r;
 
@@ -1548,15 +1546,21 @@ static int link_set_ipv6_privacy_extensions(Link *link) {
         if (!socket_ipv6_is_supported())
                 return 0;
 
-        if (!link_ipv6_privacy_extensions_enabled(link))
+        s = link_ipv6_privacy_extensions(link);
+        if (s == _IPV6_PRIVACY_EXTENSIONS_INVALID)
                 return 0;
 
         p = strjoina("/proc/sys/net/ipv6/conf/", link->ifname, "/use_tempaddr");
         xsprintf(buf, "%u", link->network->ipv6_privacy_extensions);
 
         r = write_string_file_no_create(p, buf);
-        if (r < 0)
+        if (r < 0) {
+                /* If the right value is set anyway, don't complain */
+                if (verify_one_line_file(p, buf) > 0)
+                        return 0;
+
                 log_link_warning_errno(link, r, "Cannot configure IPv6 privacy extension for interface: %m");
+        }
 
         return 0;
 }