udev: move naming-scheme.[ch] into src/shared/

That way we can use it from non-udev code too, for example nspawn.

src/shared/meson.build

@@ -130,6 +130,8 @@ shared_sources = files('''
         module-util.h
         mount-util.c
         mount-util.h
+        netif-naming-scheme.c
+        netif-naming-scheme.h
         nscd-flush.c
         nscd-flush.h
         nsflags.c

src/shared/netif-naming-scheme.c

@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "alloc-util.h"
+#include "netif-naming-scheme.h"
+#include "proc-cmdline.h"
+#include "string-util.h"
+
+static const NamingScheme naming_schemes[] = {
+        { "v238", NAMING_V238 },
+        { "v239", NAMING_V239 },
+        { "v240", NAMING_V240 },
+        { "v241", NAMING_V241 },
+        { "v243", NAMING_V243 },
+        /* … add more schemes here, as the logic to name devices is updated … */
+};
+
+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;
+}
+
+const NamingScheme* naming_scheme(void) {
+        static const NamingScheme *cache = NULL;
+        _cleanup_free_ char *buffer = NULL;
+        const char *e, *k;
+
+        if (cache)
+                return cache;
+
+        /* Acquire setting from the kernel command line */
+        (void) proc_cmdline_get_key("net.naming-scheme", 0, &buffer);
+
+        /* Also acquire it from an env var */
+        e = getenv("NET_NAMING_SCHEME");
+        if (e) {
+                if (*e == ':') {
+                        /* If prefixed with ':' the kernel cmdline takes precedence */
+                        k = buffer ?: e + 1;
+                } else
+                        k = e; /* Otherwise the env var takes precedence */
+        } else
+                k = buffer;
+
+        if (k) {
+                cache = naming_scheme_from_name(k);
+                if (cache) {
+                        log_info("Using interface naming scheme '%s'.", cache->name);
+                        return cache;
+                }
+
+                log_warning("Unknown interface naming scheme '%s' requested, ignoring.", k);
+        }
+
+        cache = naming_scheme_from_name(DEFAULT_NET_NAMING_SCHEME);
+        assert(cache);
+        log_info("Using default interface naming scheme '%s'.", cache->name);
+
+        return cache;
+}

src/shared/netif-naming-scheme.h

@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include <stdbool.h>
+
+#include "macro.h"
+
+/* So here's the deal: net_id is supposed to be an exercise in providing stable names for network devices. However, we
+ * also want to keep updating the naming scheme used in future versions of net_id. These two goals of course are
+ * contradictory: on one hand we want things to not change and on the other hand we want them to improve. Our way out
+ * of this dilemma is to introduce the "naming scheme" concept: each time we improve the naming logic we define a new
+ * flag for it. Then, we keep a list of schemes, each identified by a name associated with the flags it implements. Via
+ * a kernel command line and environment variable we then allow the user to pick the scheme they want us to follow:
+ * installers could "freeze" the used scheme at the moment of installation this way.
+ *
+ * Developers: each time you tweak the naming logic here, define a new flag below, and condition the tweak with
+ * it. Each time we do a release we'll then add a new scheme entry and include all newly defined flags.
+ *
+ * Note that this is only half a solution to the problem though: not only udev/net_id gets updated all the time, the
+ * kernel gets too. And thus a kernel that previously didn't expose some sysfs attribute we look for might eventually
+ * do, and thus affect our naming scheme too. Thus, enforcing a naming scheme will make interfacing more stable across
+ * OS versions, but not fully stabilize them. */
+typedef enum NamingSchemeFlags {
+        /* First, the individual features */
+        NAMING_SR_IOV_V            = 1 << 0, /* Use "v" suffix for SR-IOV, see 609948c7043a */
+        NAMING_NPAR_ARI            = 1 << 1, /* Use NPAR "ARI", see 6bc04997b6ea */
+        NAMING_INFINIBAND          = 1 << 2, /* Use "ib" prefix for infiniband, see 938d30aa98df */
+        NAMING_ZERO_ACPI_INDEX     = 1 << 3, /* Use zero acpi_index field, see d81186ef4f6a */
+        NAMING_ALLOW_RERENAMES     = 1 << 4, /* Allow re-renaming of devices, see #9006 */
+        NAMING_STABLE_VIRTUAL_MACS = 1 << 5, /* Use device name to generate MAC, see 6d3646406560 */
+        NAMING_NETDEVSIM           = 1 << 6, /* Generate names for netdevsim devices, see eaa9d507d855 */
+        NAMING_LABEL_NOPREFIX      = 1 << 7, /* Don't prepend ID_NET_LABEL_ONBOARD with interface type prefix */
+
+        /* And now the masks that combine the features above */
+        NAMING_V238 = 0,
+        NAMING_V239 = NAMING_V238 | NAMING_SR_IOV_V | NAMING_NPAR_ARI,
+        NAMING_V240 = NAMING_V239 | NAMING_INFINIBAND | NAMING_ZERO_ACPI_INDEX | NAMING_ALLOW_RERENAMES,
+        NAMING_V241 = NAMING_V240 | NAMING_STABLE_VIRTUAL_MACS,
+        NAMING_V243 = NAMING_V241 | NAMING_NETDEVSIM | NAMING_LABEL_NOPREFIX,
+
+        _NAMING_SCHEME_FLAGS_INVALID = -1,
+} NamingSchemeFlags;
+
+typedef struct NamingScheme {
+        const char *name;
+        NamingSchemeFlags flags;
+} NamingScheme;
+
+const NamingScheme* naming_scheme(void);
+
+static inline bool naming_scheme_has(NamingSchemeFlags flags) {
+        return FLAGS_SET(naming_scheme()->flags, flags);
+}