mount-util: introduce path_is_network_fs_harder() and use it in networkd (#35040)

Closes #32426.

src/network/networkd-manager.c

@@ -31,6 +31,7 @@
 #include "fs-util.h"
 #include "initrd-util.h"
 #include "local-addresses.h"
+#include "mount-util.h"
 #include "netlink-util.h"
 #include "network-internal.h"
 #include "networkd-address-label.h"
@@ -59,7 +60,6 @@
 #include "selinux-util.h"
 #include "set.h"
 #include "signal-util.h"
-#include "stat-util.h"
 #include "strv.h"
 #include "sysctl-util.h"
 #include "tclass.h"
@@ -508,9 +508,11 @@ static int manager_set_keep_configuration(Manager *m) {
                 return 0;
         }
 
-        r = path_is_network_fs("/");
-        if (r < 0)
-                return log_error_errno(r, "Failed to detect if root is network filesystem: %m");
+        r = path_is_network_fs_harder("/");
+        if (r < 0) {
+                log_warning_errno(r, "Failed to detect if root is network filesystem, assuming not: %m");
+                return 0;
+        }
         if (r == 0) {
                 m->keep_configuration = _KEEP_CONFIGURATION_INVALID;
                 return 0;

src/shared/mount-util.c

@@ -19,6 +19,7 @@
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
+#include "fstab-util.h"
 #include "glyph-util.h"
 #include "hashmap.h"
 #include "initrd-util.h"
@@ -1820,3 +1821,70 @@ char* umount_and_unlink_and_free(char *p) {
         (void) unlink(p);
         return mfree(p);
 }
+
+static int path_get_mount_info(
+                const char *path,
+                char **ret_fstype,
+                char **ret_options) {
+
+        _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
+        _cleanup_free_ char *fstype = NULL, *options = NULL;
+        struct libmnt_fs *fs;
+        int r;
+
+        assert(path);
+
+        table = mnt_new_table();
+        if (!table)
+                return -ENOMEM;
+
+        r = mnt_table_parse_mtab(table, /* filename = */ NULL);
+        if (r < 0)
+                return r;
+
+        fs = mnt_table_find_mountpoint(table, path, MNT_ITER_FORWARD);
+        if (!fs)
+                return -EINVAL;
+
+        if (ret_fstype) {
+                fstype = strdup(strempty(mnt_fs_get_fstype(fs)));
+                if (!fstype)
+                        return -ENOMEM;
+        }
+
+        if (ret_options) {
+                options = strdup(strempty(mnt_fs_get_options(fs)));
+                if (!options)
+                        return -ENOMEM;
+        }
+
+        if (ret_fstype)
+                *ret_fstype = TAKE_PTR(fstype);
+        if (ret_options)
+                *ret_options = TAKE_PTR(options);
+
+        return 0;
+}
+
+int path_is_network_fs_harder(const char *path) {
+        _cleanup_free_ char *fstype = NULL, *options = NULL;
+        int r, ret;
+
+        assert(path);
+
+        ret = path_is_network_fs(path);
+        if (ret > 0)
+                return true;
+
+        r = path_get_mount_info(path, &fstype, &options);
+        if (r < 0)
+                return RET_GATHER(ret, r);
+
+        if (fstype_is_network(fstype))
+                return true;
+
+        if (fstab_test_option(options, "_netdev\0"))
+                return true;
+
+        return false;
+}

src/shared/mount-util.h

@@ -180,3 +180,5 @@ unsigned long credentials_fs_mount_flags(bool ro);
 int mount_credentials_fs(const char *path, size_t size, bool ro);
 
 int make_fsmount(int error_log_level, const char *what, const char *type, unsigned long flags, const char *options, int userns_fd);
+
+int path_is_network_fs_harder(const char *path);

src/test/test-mount-util.c

@@ -537,4 +537,11 @@ TEST(bind_mount_submounts) {
         assert_se(umount_recursive(b, 0) >= 0);
 }
 
+TEST(path_is_network_fs_harder) {
+        ASSERT_OK(path_is_network_fs_harder("/"));
+        ASSERT_OK_ZERO(path_is_network_fs_harder("/dev"));
+        ASSERT_OK_ZERO(path_is_network_fs_harder("/sys"));
+        ASSERT_OK_ZERO(path_is_network_fs_harder("/run"));
+}
+
 DEFINE_TEST_MAIN(LOG_DEBUG);