initrd: avoid dynamic linking of libnvme, use dlopen() instead

As suggested during the review process, NBFT is niche and most users
won't need it. So keep the initrd generator light and only open
libnvme when any NBFT table is found.

In a typical dracut host-only scenario the nbft dracut module will
be pulled in only when NBFT is present in the system, packing in
nvme-cli and libnvme in the initramfs image.

Signed-off-by: Tomas Bzatek <tbzatek@redhat.com>

config.h.meson

@@ -282,3 +282,6 @@
 
 /* Define if NBFT support is enabled */
 #mesondefine WITH_NBFT
+
+/* Define to 1 if dlvsym() is available */
+#mesondefine HAVE_DLVSYM

meson.build

@@ -137,6 +137,9 @@ config_h.set10('HAVE_DECL_REALLOCARRAY', cc.has_function('reallocarray', prefix:
 config_h.set10('HAVE_DECL_EXPLICIT_BZERO', cc.has_function('explicit_bzero', prefix: '#include <string.h>'))
 config_h.set10('HAVE_DECL_MEMFD_CREATE', cc.has_function('memfd_create', prefix: '#include <sys/mman.h>'))
 
+config_h.set10('HAVE_DLVSYM', cc.has_function('dlvsym', prefix: '''#define _GNU_SOURCE
+                                                                   #include <dlfcn.h>'''))
+
 # types
 config_h.set('SIZEOF_PID_T', cc.sizeof('pid_t', prefix : '#include <sys/types.h>'))
 config_h.set('SIZEOF_UID_T', cc.sizeof('uid_t', prefix : '#include <sys/types.h>'))

src/nm-initrd-generator/meson.build

@@ -1,15 +1,5 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
-libnmi_deps = [
-    libnm_core_public_dep,
-]
-
-if enable_nbft
-    libnmi_deps += [
-        libnvme_dep
-    ]
-endif
-
 libnmi_core = static_library(
   'nmi-core',
   sources: files(
@@ -22,7 +12,9 @@ libnmi_core = static_library(
     src_inc,
     top_inc,
   ],
-  dependencies: libnmi_deps,
+  dependencies: [
+    libnm_core_public_dep,
+  ],
 )
 
 executable(
@@ -32,7 +24,9 @@ executable(
     src_inc,
     top_inc,
   ],
-  dependencies: libnmi_deps,
+  dependencies: [
+    libnm_core_public_dep,
+  ],
   link_with: [
     libnmi_core,
     libnm_core_aux_intern,

src/nm-initrd-generator/nmi-nbft-reader.c

@@ -10,6 +10,7 @@
 #if WITH_NBFT
 
 #include <libnvme.h>
+#include <dlfcn.h>
 
 #include "libnm-log-core/nm-logging.h"
 #include "libnm-core-intern/nm-core-internal.h"
@@ -32,6 +33,34 @@ is_valid_addr(int family, const char *addr)
             && nm_utils_ipaddr_valid(family, addr));
 }
 
+static int (*_nvme_nbft_read)(struct nbft_info **nbft, const char *filename);
+static void (*_nvme_nbft_free)(struct nbft_info *nbft);
+
+static void *
+load_libnvme(void)
+{
+    void *handle;
+
+    handle = dlopen("libnvme.so.1", RTLD_LAZY);
+    if (!handle)
+        return NULL;
+
+#if HAVE_DLVSYM
+    _nvme_nbft_read = dlvsym(handle, "nvme_nbft_read", "LIBNVME_1_5");
+    _nvme_nbft_free = dlvsym(handle, "nvme_nbft_free", "LIBNVME_1_5");
+#else
+    /* no dlvsym() in musl */
+    _nvme_nbft_read = dlsym(handle, "nvme_nbft_read");
+    _nvme_nbft_free = dlsym(handle, "nvme_nbft_free");
+#endif
+
+    if (!_nvme_nbft_read || !_nvme_nbft_free) {
+        dlclose(handle);
+        return NULL;
+    }
+    return handle;
+}
+
 static NMConnection *
 parse_hfi(struct nbft_info_hfi *hfi, int iface_idx, char **hostname)
 {
@@ -225,12 +254,13 @@ parse_hfi(struct nbft_info_hfi *hfi, int iface_idx, char **hostname)
 NMConnection **
 nmi_nbft_reader_parse(const char *sysfs_dir, char **hostname)
 {
-    GPtrArray            *a;
+    nm_auto_unref_ptrarray GPtrArray *a     = NULL;
-    gs_free char         *path  = NULL;
+    gs_free char                     *path  = NULL;
-    gs_free_error GError *error = NULL;
+    gs_free_error GError             *error = NULL;
-    GDir                 *dir;
+    GDir                             *dir;
-    const char           *entry_name;
+    void                             *libnvme_handle = NULL;
-    int                   idx = 1;
+    const char                       *entry_name;
+    int                               idx = 1;
 
     g_return_val_if_fail(sysfs_dir != NULL, NULL);
     path = g_build_filename(sysfs_dir, "firmware", "acpi", "tables", NULL);
@@ -250,8 +280,14 @@ nmi_nbft_reader_parse(const char *sysfs_dir, char **hostname)
         if (!g_str_has_prefix(entry_name, "NBFT"))
             continue;
 
+        /* attempt to load libnvme only on the first table match, saving some I/O */
+        if (!libnvme_handle && !(libnvme_handle = load_libnvme())) {
+            g_dir_close(dir);
+            return NULL;
+        }
+
         entry_path = g_build_filename(path, entry_name, NULL);
-        ret        = nvme_nbft_read(&nbft, entry_path);
+        ret        = _nvme_nbft_read(&nbft, entry_path);
         if (ret) {
             _LOGW(LOGD_CORE, "Error parsing NBFT table %s: %m", entry_path);
             continue;
@@ -274,10 +310,11 @@ nmi_nbft_reader_parse(const char *sysfs_dir, char **hostname)
                 g_ptr_array_add(a, connection);
         }
 
-        nvme_nbft_free(nbft);
+        _nvme_nbft_free(nbft);
     }
 
     g_dir_close(dir);
+    dlclose(libnvme_handle);
     g_ptr_array_add(a, NULL); /* trailing NULL-delimiter */
     return (NMConnection **) g_ptr_array_free(a, FALSE);
 }