dlopen: take log_level argument and log in fallback stubs

Every dlopen_xxx() helper now takes an int log_level argument. It is
passed through to dlopen_many_sym_or_warn() (which in turn propagates it
to dlopen_verbose() for the library-not-installed case), and is used by
the fallback stub when support for the library is not compiled in to
emit a "<lib> support is not compiled in." message at the caller's level.
Callers pass LOG_DEBUG when gracefully degrading, or a higher level when
the failure should surface, and no longer need to log redundantly at the
call site.

As part of this, dlopen_bpf_full() (which already took a log_level) is
merged into dlopen_bpf() rather than keeping both.

The static inline fallbacks used to live in the headers, which required
pulling log.h in from every header that declared a dlopen_xxx(). Move
them into the .c files instead: the declaration is always outside the
#if HAVE_XXX block, the impl sits outside the outer #if HAVE_XXX wrap
with its own internal #if HAVE_XXX/#else/#endif, and apparmor-util.c,
idn-util.c, libmount-util.c and pam-util.c are now always compiled so
they can host their stubs.

src/core/bpf-bind-iface.c

@@ -31,7 +31,7 @@ int bpf_bind_network_interface_supported(void) {
         if (supported >= 0)
                 return supported;
 
-        if (dlopen_bpf_full(LOG_WARNING) < 0)
+        if (dlopen_bpf(LOG_WARNING) < 0)
                 return (supported = false);
 
         obj = bind_iface_bpf__open();

src/core/bpf-restrict-fs.c

@@ -91,7 +91,7 @@ bool bpf_restrict_fs_supported(bool initialize) {
         if (!initialize)
                 return false;
 
-        if (dlopen_bpf_full(LOG_WARNING) < 0)
+        if (dlopen_bpf(LOG_WARNING) < 0)
                 return (supported = false);
 
         r = lsm_supported("bpf");

src/core/bpf-restrict-ifaces.c

@@ -86,7 +86,7 @@ int bpf_restrict_ifaces_supported(void) {
         if (supported >= 0)
                 return supported;
 
-        if (dlopen_bpf_full(LOG_WARNING) < 0)
+        if (dlopen_bpf(LOG_WARNING) < 0)
                 return (supported = false);
 
         r = prepare_restrict_ifaces_bpf(NULL, true, NULL, &obj);

src/core/bpf-socket-bind.c

@@ -125,7 +125,7 @@ int bpf_socket_bind_supported(void) {
         _cleanup_(socket_bind_bpf_freep) struct socket_bind_bpf *obj = NULL;
         int r;
 
-        if (dlopen_bpf_full(LOG_WARNING) < 0)
+        if (dlopen_bpf(LOG_WARNING) < 0)
                 return false;
 
         r = prepare_socket_bind_bpf(/* unit= */ NULL, /* allow_rules= */ NULL, /* deny_rules= */ NULL, &obj);

src/core/exec-invoke.c

@@ -1359,9 +1359,9 @@ static int setup_pam(
          * parent process will exec() the actual daemon. We do things this way to ensure that the main PID of
          * the daemon is the one we initially fork()ed. */
 
-        r = dlopen_libpam();
+        r = dlopen_libpam(LOG_ERR);
         if (r < 0)
-                return log_error_errno(r, "PAM support not available: %m");
+                return r;
 
         r = barrier_create(&barrier);
         if (r < 0)
@@ -1625,7 +1625,7 @@ static bool seccomp_allows_drop_privileges(const ExecContext *c) {
         assert(c);
 
         /* No libseccomp, all is fine */
-        if (dlopen_libseccomp() < 0)
+        if (dlopen_libseccomp(LOG_DEBUG) < 0)
                 return true;
 
         /* No syscall filter, we are allowed to drop privileges */
@@ -1927,7 +1927,7 @@ static int apply_restrict_filesystems(const ExecContext *c, const ExecParameters
         }
 
         /* We are in a new binary, so dl-open again */
-        r = dlopen_bpf();
+        r = dlopen_bpf(LOG_DEBUG);
         if (r < 0)
                 return r;
 
@@ -6026,10 +6026,10 @@ int exec_invoke(
         }
 
         /* Load a bunch of libraries we'll possibly need later, before we turn off dlopen() */
-        (void) dlopen_bpf();
-        (void) dlopen_cryptsetup();
-        (void) dlopen_libmount();
-        (void) dlopen_libseccomp();
+        (void) dlopen_bpf(LOG_DEBUG);
+        (void) dlopen_cryptsetup(LOG_DEBUG);
+        (void) dlopen_libmount(LOG_DEBUG);
+        (void) dlopen_libseccomp(LOG_DEBUG);
 
         /* Let's now disable further dlopen()ing of libraries, since we are about to do namespace
          * shenanigans, and do not want to mix resources from host and namespace */

src/core/execute.c

@@ -1491,7 +1491,7 @@ void exec_context_dump(const ExecContext *c, FILE* f, const char *prefix) {
                         fputc('~', f);
 
 #if HAVE_SECCOMP
-                if (dlopen_libseccomp() >= 0) {
+                if (dlopen_libseccomp(LOG_DEBUG) >= 0) {
                         void *id, *val;
                         bool first = true;
                         HASHMAP_FOREACH_KEY(val, id, c->syscall_filter) {
@@ -1910,7 +1910,7 @@ char** exec_context_get_syscall_filter(const ExecContext *c) {
         assert(c);
 
 #if HAVE_SECCOMP
-        if (dlopen_libseccomp() < 0)
+        if (dlopen_libseccomp(LOG_DEBUG) < 0)
                 return strv_new(NULL);
 
         void *id, *val;
@@ -1979,7 +1979,7 @@ char** exec_context_get_syscall_log(const ExecContext *c) {
         assert(c);
 
 #if HAVE_SECCOMP
-        if (dlopen_libseccomp() < 0)
+        if (dlopen_libseccomp(LOG_DEBUG) < 0)
                 return strv_new(NULL);
 
         void *id, *val;

src/core/main.c

@@ -3378,7 +3378,7 @@ int main(int argc, char *argv[]) {
         }
 
         /* Building without libmount is allowed, but if it is compiled in, then we must be able to load it */
-        r = dlopen_libmount();
+        r = dlopen_libmount(LOG_DEBUG);
         if (r < 0 && !ERRNO_IS_NEG_NOT_SUPPORTED(r)) {
                 error_message = "Failed to load libmount.so";
                 goto finish;

src/core/mount.c

@@ -2408,7 +2408,7 @@ static int mount_test_startable(Unit *u) {
 }
 
 static bool mount_supported(void) {
-        return dlopen_libmount() >= 0;
+        return dlopen_libmount(LOG_DEBUG) >= 0;
 }
 
 static int mount_subsystem_ratelimited(Manager *m) {

src/core/namespace.c

@@ -3984,7 +3984,7 @@ int refresh_extensions_in_namespace(
         if (r > 0)
                 return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Target namespace is not separate, cannot reload extensions");
 
-        (void) dlopen_cryptsetup();
+        (void) dlopen_cryptsetup(LOG_DEBUG);
 
         extension_dir = path_join(p->private_namespace_dir, "unit-extensions");
         if (!extension_dir)

src/core/selinux-setup.c

@@ -17,11 +17,9 @@ int mac_selinux_setup(bool *loaded_policy) {
 
         assert(loaded_policy);
 
-        r = dlopen_libselinux();
-        if (r < 0) {
-                log_debug_errno(r, "No SELinux library available, skipping setup.");
+        r = dlopen_libselinux(LOG_DEBUG);
+        if (r < 0)
                 return 0;
-        }
 
         mac_selinux_disable_logging();