258 lines
12 KiB
Diff
258 lines
12 KiB
Diff
From 08ac9f7f55c138678c6415139e7510a05a75b81d Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Michal=20Sekleta=CC=81r?= <msekleta@redhat.com>
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Date: Wed, 14 Oct 2020 16:57:44 +0200
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Subject: [PATCH] udev: introduce udev net_id "naming schemes"
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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With this we can stabilize how naming works for network interfaces. A
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user can request through a kernel cmdline option or an env var which
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scheme to follow. The idea is that installers use this to set into stone
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(a very soft stone though) the scheme used during installation so that
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interface naming doesn't change afterwards anymore.
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Why use env vars and kernel cmdline options, and not a config file of
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its own?
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Well, first of all there's no obvious existing one to use. But more
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importantly: I have the feeling that this logic is kind of an incomplete
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hack, and I simply don't want to do advertise this as a perfectly
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working solution. So far we used env vars for the non-so-official
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options and proper config files for the official stuff. Given how
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incomplete this logic is (i.e. the big variable for naming remains the
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kernel, which might expose sysfs attributes in newer versions that we
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check for and didn't exist in older versions — and other problems like
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this), I am simply not confident in giving this first-class exposure in
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a primary configuration file.
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Fixes: #10448
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(cherry-picked from commit f7e81fd96fdfe0ac6dcdb72de43f7cb4720e363a)
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Related: #1827462
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[msekleta: note that we are introducing our own naming schemes based on
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RHEL-8 minor versions. Also we are not backporting all naming scheme
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features that appeared in the original commit. We are backporting only
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features relevant for v239 while original commit also converted
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changes introduced in v240 into naming scheme flags.]
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---
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doc/ENVIRONMENT.md | 9 +++
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man/kernel-command-line.xml | 1 +
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man/systemd-udevd.service.xml | 16 +++++
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src/udev/udev-builtin-net_id.c | 106 ++++++++++++++++++++++++++++++++-
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4 files changed, 130 insertions(+), 2 deletions(-)
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diff --git a/doc/ENVIRONMENT.md b/doc/ENVIRONMENT.md
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index 39a36a52cc..1a4aa01ef4 100644
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--- a/doc/ENVIRONMENT.md
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+++ b/doc/ENVIRONMENT.md
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@@ -76,6 +76,15 @@ systemd-logind:
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hibernation is available even if the swap devices do not provide enough room
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for it.
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+* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
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+ v238, v239, v240 …) as parameter. If specified udev's net_id builtin will
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+ follow the specified naming scheme when determining stable network interface
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+ names. This may be used to revert to naming schemes of older udev versions,
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+ in order to provide more stable naming across updates. This environment
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+ variable takes precedence over the kernel command line option
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+ `net.naming-scheme=`, except if the value is prefixed with `:` in which case
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+ the kernel command line option takes precedence, if it is specified as well.
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+
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installed systemd tests:
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* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
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diff --git a/man/kernel-command-line.xml b/man/kernel-command-line.xml
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index 4d8cb4e50e..b753d0592c 100644
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--- a/man/kernel-command-line.xml
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+++ b/man/kernel-command-line.xml
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@@ -246,6 +246,7 @@
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<term><varname>udev.event_timeout=</varname></term>
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<term><varname>rd.udev.event_timeout=</varname></term>
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<term><varname>net.ifnames=</varname></term>
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+ <term><varname>net.naming-scheme=</varname></term>
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<listitem>
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<para>Parameters understood by the device event managing
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diff --git a/man/systemd-udevd.service.xml b/man/systemd-udevd.service.xml
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index 73c77ea690..6449103441 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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@@ -170,6 +170,22 @@
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when possible. It is enabled by default; specifying 0 disables it.</para>
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</listitem>
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</varlistentry>
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+ <varlistentry>
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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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+ </listitem>
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+ </varlistentry>
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</variablelist>
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<!-- when adding entries here, consider also adding them
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in kernel-command-line.xml -->
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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 147e04ab8c..148696183e 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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@@ -96,6 +96,7 @@
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#include "fileio.h"
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#include "fs-util.h"
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#include "parse-util.h"
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+#include "proc-cmdline.h"
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#include "stdio-util.h"
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#include "string-util.h"
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#include "udev.h"
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@@ -103,6 +104,52 @@
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#define ONBOARD_INDEX_MAX (16*1024-1)
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+/* So here's the deal: net_id is supposed to be an excercise in providing stable names for network devices. However, we
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+ * also want to keep updating the naming scheme used in future versions of net_id. These two goals of course are
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+ * contradictory: on one hand we want things to not change and on the other hand we want them to improve. Our way out
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+ * of this dilemma is to introduce the "naming scheme" concept: each time we improve the naming logic we define a new
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+ * flag for it. Then, we keep a list of schemes, each identified by a name associated with the flags it implements. Via
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+ * a kernel command line and environment variable we then allow the user to pick the scheme they want us to follow:
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+ * installers could "freeze" the used scheme at the moment of installation this way.
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+ *
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+ * Developers: each time you tweak the naming logic here, define a new flag below, and condition the tweak with
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+ * it. Each time we do a release we'll then add a new scheme entry and include all newly defined flags.
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+ *
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+ * Note that this is only half a solution to the problem though: not only udev/net_id gets updated all the time, the
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+ * kernel gets too. And thus a kernel that previously didn't expose some sysfs attribute we look for might eventually
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+ * do, and thus affect our naming scheme too. Thus, enforcing a naming scheme will make interfacing more stable across
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+ * OS versions, but not fully stabilize them. */
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+typedef enum NamingSchemeFlags {
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+ /* First, the individual features */
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+ NAMING_SR_IOV_V = 1 << 0, /* Use "v" suffix for SR-IOV, see 609948c7043a40008b8299529c978ed8e11de8f6*/
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+ NAMING_NPAR_ARI = 1 << 1, /* Use NPAR "ARI", see 6bc04997b6eab35d1cb9fa73889892702c27be09 */
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+
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+ /* And now the masks that combine the features above */
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+ NAMING_V238 = 0,
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+ NAMING_V239 = NAMING_V238|NAMING_SR_IOV_V|NAMING_NPAR_ARI,
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+ NAMING_RHEL_8_0 = NAMING_V239,
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+ NAMING_RHEL_8_1 = NAMING_V239,
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+ NAMING_RHEL_8_2 = NAMING_V239,
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+ NAMING_RHEL_8_3 = NAMING_V239,
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+
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+ _NAMING_SCHEME_FLAGS_INVALID = -1,
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+} NamingSchemeFlags;
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+
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+typedef struct NamingScheme {
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+ const char *name;
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+ NamingSchemeFlags flags;
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+} NamingScheme;
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+
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+static const NamingScheme naming_schemes[] = {
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+ { "v238", NAMING_V238 },
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+ { "v239", NAMING_V239 },
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+ { "rhel-8.0", NAMING_RHEL_8_0 },
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+ { "rhel-8.1", NAMING_RHEL_8_1 },
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+ { "rhel-8.2", NAMING_RHEL_8_2 },
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+ { "rhel-8.3", NAMING_RHEL_8_3 },
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+ /* … add more schemes here, as the logic to name devices is updated … */
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+};
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+
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enum netname_type{
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NET_UNDEF,
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NET_PCI,
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@@ -138,6 +185,56 @@ struct virtfn_info {
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char suffix[IFNAMSIZ];
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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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+ const char *e, *k;
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+
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+ if (cache)
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+ return cache;
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+
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+ /* Acquire setting from the kernel command line */
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+ (void) proc_cmdline_get_key("net.naming-scheme", 0, &buffer);
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+
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+ /* Also acquire it from an env var */
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+ e = getenv("NET_NAMING_SCHEME");
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+ if (e) {
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+ if (*e == ':') {
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+ /* If prefixed with ':' the kernel cmdline takes precedence */
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+ k = buffer ?: e + 1;
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+ } else
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+ k = e; /* Otherwise the env var takes precedence */
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+ } else
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+ k = buffer;
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+
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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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+
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+ if (!cache)
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+ log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
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+ }
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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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+
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+ return cache;
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+}
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+
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+static bool naming_scheme_has(NamingSchemeFlags flags) {
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+ return FLAGS_SET(naming_scheme()->flags, flags);
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+}
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+
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/* skip intermediate virtio devices */
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static struct udev_device *skip_virtio(struct udev_device *dev) {
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struct udev_device *parent = dev;
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@@ -299,7 +396,9 @@ static int dev_pci_slot(struct udev_device *dev, struct netnames *names) {
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if (sscanf(udev_device_get_sysname(names->pcidev), "%x:%x:%x.%u", &domain, &bus, &slot, &func) != 4)
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return -ENOENT;
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- if (is_pci_ari_enabled(names->pcidev))
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+
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+ if (naming_scheme_has(NAMING_NPAR_ARI) &&
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+ is_pci_ari_enabled(names->pcidev))
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/* ARI devices support up to 256 functions on a single device ("slot"), and interpret the
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* traditional 5-bit slot and 3-bit function number as a single 8-bit function number,
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* where the slot makes up the upper 5 bits. */
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@@ -494,7 +593,8 @@ static int names_pci(struct udev_device *dev, struct netnames *names) {
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return -ENOENT;
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}
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- if (get_virtfn_info(dev, names, &vf_info) >= 0) {
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+ if (naming_scheme_has(NAMING_SR_IOV_V) &&
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+ get_virtfn_info(dev, names, &vf_info) >= 0) {
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/* If this is an SR-IOV virtual device, get base name using physical device and add virtfn suffix. */
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vf_names.pcidev = vf_info.physfn_pcidev;
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dev_pci_onboard(dev, &vf_names);
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@@ -741,6 +841,8 @@ static int builtin_net_id(struct udev_device *dev, int argc, char *argv[], bool
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prefix = "ww";
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}
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+ udev_builtin_add_property(dev, test, "ID_NET_NAMING_SCHEME", naming_scheme()->name);
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+
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err = names_mac(dev, &names);
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if (err >= 0 && names.mac_valid) {
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char str[IFNAMSIZ];
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