userns-restrict: Move HAVE_VMLINUX check into functions

Let's do these checks like we try to do them elsewhere, in the
function, not outside. This avoids having to declare the function
arguments twice and keeps the logic for each function together
instead of spread out across the file.

src/nsresourced/userns-restrict.c

@@ -1,10 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include "log.h"
-#include "userns-restrict.h"
-
-#if HAVE_VMLINUX_H
-
 #include <sched.h>
 #include <sys/mount.h>
 
@@ -12,12 +7,14 @@
 #include "bpf-link.h"
 #include "fd-util.h"
 #include "fs-util.h"
+#include "log.h"
 #include "lsm-util.h"
 #include "mkdir.h"
 #include "mount-util.h"
 #include "mountpoint-util.h"
 #include "namespace-util.h"
 #include "path-util.h"
+#include "userns-restrict.h"
 
 #define USERNS_MAX (16U*1024U)
 #define MOUNTS_MAX 4096U
@@ -26,10 +23,14 @@
 #define MAP_LINK_PREFIX "/sys/fs/bpf/systemd/userns-restrict/maps"
 
 struct userns_restrict_bpf *userns_restrict_bpf_free(struct userns_restrict_bpf *obj) {
+#if HAVE_VMLINUX_H
         (void) userns_restrict_bpf__destroy(obj); /* this call is fine with NULL */
+#endif
         return NULL;
+
 }
 
+#if HAVE_VMLINUX_H
 static int make_inner_hash_map(void) {
         int fd;
 
@@ -45,11 +46,13 @@ static int make_inner_hash_map(void) {
 
         return fd;
 }
+#endif
 
 int userns_restrict_install(
                 bool pin,
                 struct userns_restrict_bpf **ret) {
 
+#if HAVE_VMLINUX_H
         _cleanup_(userns_restrict_bpf_freep) struct userns_restrict_bpf *obj = NULL;
         _cleanup_close_ int dummy_mnt_id_hash_fd = -EBADF;
         int r;
@@ -176,6 +179,9 @@ int userns_restrict_install(
                 *ret = TAKE_PTR(obj);
 
         return 0;
+#else
+        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
+#endif
 }
 
 int userns_restrict_put_by_inode(
@@ -185,6 +191,7 @@ int userns_restrict_put_by_inode(
                 const int mount_fds[],
                 size_t n_mount_fds) {
 
+#if HAVE_VMLINUX_H
         _cleanup_close_ int inner_map_fd = -EBADF;
         _cleanup_free_ int *mnt_ids = NULL;
         uint64_t ino = userns_inode;
@@ -268,6 +275,9 @@ int userns_restrict_put_by_inode(
         }
 
         return 0;
+#else
+        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
+#endif
 }
 
 int userns_restrict_put_by_fd(
@@ -277,6 +287,7 @@ int userns_restrict_put_by_fd(
                 const int mount_fds[],
                 size_t n_mount_fds) {
 
+#if HAVE_VMLINUX_H
         struct stat st;
         int r;
 
@@ -299,12 +310,16 @@ int userns_restrict_put_by_fd(
                         replace,
                         mount_fds,
                         n_mount_fds);
+#else
+        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
+#endif
 }
 
 int userns_restrict_reset_by_inode(
                 struct userns_restrict_bpf *obj,
                 uint64_t ino) {
 
+#if HAVE_VMLINUX_H
         int r, outer_map_fd;
         unsigned u;
 
@@ -325,26 +340,7 @@ int userns_restrict_reset_by_inode(
                 return log_debug_errno(r, "Failed to remove entry for inode %" PRIu64 " from outer map: %m", ino);
 
         return 0;
-}
-
 #else
-int userns_restrict_install(bool pin, struct userns_restrict_bpf **ret) {
         return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
-}
-
-struct userns_restrict_bpf *userns_restrict_bpf_free(struct userns_restrict_bpf *obj) {
-        return NULL;
-}
-
-int userns_restrict_put_by_fd(struct userns_restrict_bpf *obj, int userns_fd, bool replace, const int mount_fds[], size_t n_mount_fds) {
-        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
-}
-
-int userns_restrict_put_by_inode(struct userns_restrict_bpf *obj, uint64_t userns_inode, bool replace, const int mount_fds[], size_t n_mount_fds) {
-        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
-}
-
-int userns_restrict_reset_by_inode(struct userns_restrict_bpf *obj, uint64_t userns_inode) {
-        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "User Namespace Restriction BPF support disabled.");
-}
 #endif
+}