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meson: make net.naming-scheme= default configurable 

This is useful for distributions, where the stability of interface names should
be preseved after an upgrade of systemd. So when some specific release of the
distro is made available, systemd defaults to the latest & greatest naming
scheme, and subsequent updates set the same default. This default may still
be overriden through the kernel and env var options.

A special value "latest" is also allowed. Without a specific name, it is harder
to verride from meson. In case of 'combo' options, meson reads the default
during the initial configuration, and "remembers" this choice. When systemd is
updated, old build/ directories could keep the old default, which would be
annoying. Hence, "latest" is introduced to make it explicit, yet follow the
upstream. This is actually useful for the user too, because it may be used
as an override, without having to actually specify a version.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2018-12-11 23:28:29 +01:00 committed by Lennart Poettering
parent f7e81fd96f
commit 06da5c63dd
5 changed files with 51 additions and 32 deletions
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15
docs/ENVIRONMENT.md
View File

@ -92,13 +92,14 @@ systemd-logind:
for it.
* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
v238, v239, v240 …) as parameter. If specified udev's net_id builtin will
follow the specified naming scheme when determining stable network interface
names. This may be used to revert to naming schemes of older udev versions,
in order to provide more stable naming across updates. This environment
variable takes precedence over the kernel command line option
`net.naming-scheme=`, except if the value is prefixed with `:` in which case
the kernel command line option takes precedence, if it is specified as well.
"v238", "v239", "v240"…, or the special value "latest") as parameter. If
specified udev's net_id builtin will follow the specified naming scheme when
determining stable network interface names. This may be used to revert to
naming schemes of older udev versions, in order to provide more stable naming
across updates. This environment variable takes precedence over the kernel
command line option `net.naming-scheme=`, except if the value is prefixed
with `:` in which case the kernel command line option takes precedence, if it
is specified as well.
installed systemd tests:

24
man/systemd-udevd.service.xml
View File

@ -174,16 +174,20 @@
<term><varname>net.naming-scheme=</varname></term>
<listitem>
<para>Network interfaces are renamed to give them predictable names when possible (unless
<varname>net.ifnames=0</varname> is specified, see above). The names are derived from various device metadata
fields. Newer versions of <filename>systemd-udevd.service</filename> take more of these fields into account,
improving (and thus possibly changing) the names used for the same devices. With this kernel command line
option it is possible to pick a specific version of this algorithm. It expects a naming scheme identifier as
argument. Currently the following identifiers are known: <literal>v238</literal>, <literal>v239</literal>,
<literal>v240</literal> which each implement the naming scheme that was the default in the indicated systemd
version. Note that selecting a specific scheme is not sufficient to fully stabilize interface naming: the
naming is generally derived from driver attributes exposed by the kernel. As the kernel is updated,
previously missing attributes <filename>systemd-udevd.service</filename> is checking might appear, which
affects older name derivation algorithms, too.</para>
<varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
these fields into account, improving (and thus possibly changing) the names used for the same
devices. With this kernel command line option it is possible to pick a specific version of this
algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
are known: <literal>v238</literal>, <literal>v239</literal>, <literal>v240</literal> which each
implement the naming scheme that was the default in the indicated systemd version. In addition,
<literal>latest</literal> may be used to designate the latest scheme known (to this particular
version of <filename>systemd-udevd.service</filename>).</para>
<para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
appear, which affects older name derivation algorithms, too.</para>
</listitem>
</varlistentry>
</variablelist>

4
meson.build
View File

@ -694,6 +694,9 @@ else
conf.set('DEFAULT_HIERARCHY', 'CGROUP_UNIFIED_ALL')
endif
default_net_naming_scheme = get_option('default-net-naming-scheme')
conf.set_quoted('DEFAULT_NET_NAMING_SCHEME', default_net_naming_scheme)
time_epoch = get_option('time-epoch')
if time_epoch == -1
NEWS = files('NEWS')
@ -3093,6 +3096,7 @@ status = [
'default DNSSEC mode: @0@'.format(default_dnssec),
'default DNS-over-TLS mode: @0@'.format(default_dns_over_tls),
'default cgroup hierarchy: @0@'.format(default_hierarchy),
'default net.naming-scheme setting: @0@'.format(default_net_naming_scheme),
'default KillUserProcesses setting: @0@'.format(kill_user_processes)]
alt_dns_servers = '\n '.join(dns_servers.split(' '))

3
meson_options.txt
View File

@ -156,6 +156,9 @@ option('compat-gateway-hostname', type : 'boolean', value : 'false',
option('default-hierarchy', type : 'combo',
choices : ['legacy', 'hybrid', 'unified'], value : 'hybrid',
description : 'default cgroup hierarchy')
option('default-net-naming-scheme', type : 'combo',
choices : ['latest', 'v238', 'v239', 'v240'],
description : 'default net.naming-scheme= value')
option('time-epoch', type : 'integer', value : '-1',
description : 'time epoch for time clients')
option('system-uid-max', type : 'integer', value : '-1',

37
src/udev/udev-builtin-net_id.c
View File

@ -193,6 +193,19 @@ struct virtfn_info {
char suffix[IFNAMSIZ];
};
static const NamingScheme* naming_scheme_from_name(const char *name) {
size_t i;
if (streq(name, "latest"))
return naming_schemes + ELEMENTSOF(naming_schemes) - 1;
for (i = 0; i < ELEMENTSOF(naming_schemes); i++)
if (streq(naming_schemes[i].name, name))
return naming_schemes + i;
return NULL;
}
static const NamingScheme* naming_scheme(void) {
static const NamingScheme *cache = NULL;
_cleanup_free_ char *buffer = NULL;
@ -216,24 +229,18 @@ static const NamingScheme* naming_scheme(void) {
k = buffer;
if (k) {
size_t i;
cache = naming_scheme_from_name(k);
if (cache) {
log_info("Using interface naming scheme '%s'.", cache->name);
return cache;
}
for (i = 0; i < ELEMENTSOF(naming_schemes); i++)
if (streq(naming_schemes[i].name, k)) {
cache = naming_schemes + i;
break;
}
if (!cache)
log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
}
if (cache)
log_info("Using interface naming scheme '%s'.", cache->name);
else {
cache = naming_schemes + ELEMENTSOF(naming_schemes) - 1;
log_info("Using default interface naming scheme '%s'.", cache->name);
}
cache = naming_scheme_from_name(DEFAULT_NET_NAMING_SCHEME);
assert(cache);
log_info("Using default interface naming scheme '%s'.", cache->name);
return cache;
}