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From 8c263758fe196624005f19bd6f46d63e3841c5be Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Tue, 11 Dec 2018 23:28:29 +0100
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Subject: [PATCH] meson: make net.naming-scheme= default configurable
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This is useful for distributions, where the stability of interface names should
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be preseved after an upgrade of systemd. So when some specific release of the
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distro is made available, systemd defaults to the latest & greatest naming
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scheme, and subsequent updates set the same default. This default may still
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be overriden through the kernel and env var options.
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A special value "latest" is also allowed. Without a specific name, it is harder
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to verride from meson. In case of 'combo' options, meson reads the default
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during the initial configuration, and "remembers" this choice. When systemd is
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updated, old build/ directories could keep the old default, which would be
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annoying. Hence, "latest" is introduced to make it explicit, yet follow the
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upstream. This is actually useful for the user too, because it may be used
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as an override, without having to actually specify a version.
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(cherry picked from commit 06da5c63dd697ea4087e76c6d809b60b5780b87c)
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Related: #1827462
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[msekleta: note that our default is not latest but rhel-8.0]
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---
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 doc/ENVIRONMENT.md             | 15 +++++++-------
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 man/systemd-udevd.service.xml  | 24 ++++++++++++---------
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 meson.build                    |  4 ++++
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 meson_options.txt              |  3 +++
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 src/udev/udev-builtin-net_id.c | 38 ++++++++++++++++++++--------------
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 5 files changed, 51 insertions(+), 33 deletions(-)
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diff --git a/doc/ENVIRONMENT.md b/doc/ENVIRONMENT.md
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index 1a4aa01ef4..0e763b6302 100644
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--- a/doc/ENVIRONMENT.md
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+++ b/doc/ENVIRONMENT.md
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@@ -77,13 +77,14 @@ systemd-logind:
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   for it.
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 * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
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-  v238, v239, v240 …) as parameter. If specified udev's net_id builtin will
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-  follow the specified naming scheme when determining stable network interface
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-  names. This may be used to revert to naming schemes of older udev versions,
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-  in order to provide more stable naming across updates. This environment
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-  variable takes precedence over the kernel command line option
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-  `net.naming-scheme=`, except if the value is prefixed with `:` in which case
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-  the kernel command line option takes precedence, if it is specified as well.
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+  "rhel-8.0", "rhel-8.1", "rhel-8.2"…, or the special value "latest") as
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+  parameter. If specified udev's net_id builtin will follow the specified
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+  naming scheme when determining stable network interface names. This may be
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+  used to revert to naming schemes of older udev versions, in order to provide
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+  more stable naming across updates. This environment variable takes precedence
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+  over the kernel command line option `net.naming-scheme=`, except if the value
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+  is prefixed with `:` in which case the kernel command line option takes
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+  precedence, if it is specified as well.
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 installed systemd tests:
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diff --git a/man/systemd-udevd.service.xml b/man/systemd-udevd.service.xml
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index 6449103441..b738591c93 100644
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--- a/man/systemd-udevd.service.xml
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+++ b/man/systemd-udevd.service.xml
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@@ -174,16 +174,20 @@
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         <term><varname>net.naming-scheme=</varname></term>
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         <listitem>
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           <para>Network interfaces are renamed to give them predictable names when possible (unless
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-          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various device metadata
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-          fields. Newer versions of <filename>systemd-udevd.service</filename> take more of these fields into account,
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-          improving (and thus possibly changing) the names used for the same devices. With this kernel command line
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-          option it is possible to pick a specific version of this algorithm. It expects a naming scheme identifier as
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-          argument. Currently the following identifiers are known: <literal>v238</literal>, <literal>v239</literal>,
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-          <literal>v240</literal> which each implement the naming scheme that was the default in the indicated systemd
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-          version. Note that selecting a specific scheme is not sufficient to fully stabilize interface naming: the
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-          naming is generally derived from driver attributes exposed by the kernel. As the kernel is updated,
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-          previously missing attributes <filename>systemd-udevd.service</filename> is checking might appear, which
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-          affects older name derivation algorithms, too.</para>
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+          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
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+          device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
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+          these fields into account, improving (and thus possibly changing) the names used for the same
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+          devices. With this kernel command line option it is possible to pick a specific version of this
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+          algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
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+          are known: <literal>rhel-8.0</literal>, <literal>rhel-8.1</literal>, <literal>rhel-8.2</literal>,
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+          <literal>rhel-8.3</literal> which each implement the naming scheme that was the default in the
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+          indicated Red Hat Enterprise Linux minor version. In addition, <literal>latest</literal> may be
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+          used to designate the latest scheme known (to this particular version of
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+          <filename>systemd-udevd.service</filename>).</para>
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+          <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
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+          the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
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+          updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
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+          appear, which affects older name derivation algorithms, too.</para>
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         </listitem>
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       </varlistentry>
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     </variablelist>
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diff --git a/meson.build b/meson.build
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index 65c1d0785e..57de947367 100644
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--- a/meson.build
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+++ b/meson.build
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@@ -639,6 +639,9 @@ else
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         conf.set('DEFAULT_HIERARCHY', 'CGROUP_UNIFIED_ALL')
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 endif
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+default_net_naming_scheme = get_option('default-net-naming-scheme')
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+conf.set_quoted('DEFAULT_NET_NAMING_SCHEME', default_net_naming_scheme)
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+
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 time_epoch = get_option('time-epoch')
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 if time_epoch == ''
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         NEWS = files('NEWS')
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@@ -2925,6 +2928,7 @@ status = [
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         'default DNSSEC mode:               @0@'.format(default_dnssec),
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         'default DNS-over-TLS mode:         @0@'.format(default_dns_over_tls),
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         'default cgroup hierarchy:          @0@'.format(default_hierarchy),
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+        'default net.naming-scheme setting: @0@'.format(default_net_naming_scheme),
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         'default KillUserProcesses setting: @0@'.format(kill_user_processes)]
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 alt_dns_servers = '\n                                            '.join(dns_servers.split(' '))
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diff --git a/meson_options.txt b/meson_options.txt
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index 0996891177..213079ac15 100644
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--- a/meson_options.txt
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+++ b/meson_options.txt
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@@ -158,6 +158,9 @@ option('default-hierarchy', type : 'combo',
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        description : 'default cgroup hierarchy')
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 option('time-epoch', type : 'string',
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        description : 'time epoch for time clients')
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+option('default-net-naming-scheme', type : 'combo',
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+       choices : ['rhel-8.0', 'rhel-8.1', 'rhel-8.2', 'rhel-8.3', 'latest'],
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+       description : 'default net.naming-scheme= value')
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 option('system-uid-max', type : 'string',
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        description : 'maximum system UID')
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 option('system-gid-max', type : 'string',
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diff --git a/src/udev/udev-builtin-net_id.c b/src/udev/udev-builtin-net_id.c
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index 148696183e..d85dc2848b 100644
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--- a/src/udev/udev-builtin-net_id.c
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+++ b/src/udev/udev-builtin-net_id.c
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@@ -185,6 +185,19 @@ struct virtfn_info {
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         char suffix[IFNAMSIZ];
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 };
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+static const NamingScheme* naming_scheme_from_name(const char *name) {
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+        size_t i;
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+
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+        if (streq(name, "latest"))
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+                return naming_schemes + ELEMENTSOF(naming_schemes) - 1;
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+
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+        for (i = 0; i < ELEMENTSOF(naming_schemes); i++)
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+                if (streq(naming_schemes[i].name, name))
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+                        return naming_schemes + i;
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+
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+        return NULL;
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+}
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+
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 static const NamingScheme* naming_scheme(void) {
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         static const NamingScheme *cache = NULL;
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         _cleanup_free_ char *buffer = NULL;
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@@ -208,25 +221,18 @@ static const NamingScheme* naming_scheme(void) {
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                 k = buffer;
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         if (k) {
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-                size_t i;
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-
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-                for (i = 0; i < ELEMENTSOF(naming_schemes); i++)
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-                        if (streq(naming_schemes[i].name, k)) {
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-                                cache = naming_schemes + i;
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-                                break;
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-                        }
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+                cache = naming_scheme_from_name(k);
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+                if (cache) {
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+                        log_info("Using interface naming scheme '%s'.", cache->name);
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+                        return cache;
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+                }
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-                if (!cache)
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-                        log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
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+                log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
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         }
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-        if (cache)
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-                log_info("Using interface naming scheme '%s'.", cache->name);
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-        else {
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-                /* RHEL-only: here we differ from the upstream and if no naming scheme was selected we default to naming from systemd-239 */
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-                cache = &naming_schemes[2];
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-                log_info("Using default interface naming scheme '%s'.", cache->name);
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-        }
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+        cache = naming_scheme_from_name(DEFAULT_NET_NAMING_SCHEME);
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+        assert(cache);
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+        log_info("Using default interface naming scheme '%s'.", cache->name);
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         return cache;
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 }