generator: skip fsck if fsck command is missing

This is useful for systems which don't have any fsck.

We already skip emitting the fsck dependency when the fsck.$fstype helper
is missing, but fstab-generator doesn't necessarily know the fstype when
handling the root= parameter.

Previously, systemd-fsck was started for these mounts and then exited
immediately because it couldn't find the fsck.$fstype helper.

src/basic/path-util.c

@@ -782,14 +782,23 @@ static int executable_is_good(const char *executable) {
                                "/dev/null");
 }
 
-int fsck_exists(const char *fstype) {
+int fsck_exists(void) {
+        return executable_is_good("fsck");
+}
+
+int fsck_exists_for_fstype(const char *fstype) {
         const char *checker;
+        int r;
 
         assert(fstype);
 
         if (streq(fstype, "auto"))
                 return -EINVAL;
 
+        r = fsck_exists();
+        if (r <= 0)
+                return r;
+
         checker = strjoina("fsck.", fstype);
         return executable_is_good(checker);
 }

src/basic/path-util.h

@@ -103,7 +103,8 @@ static inline int find_executable(const char *name, char **ret_filename) {
 
 bool paths_check_timestamp(const char* const* paths, usec_t *paths_ts_usec, bool update);
 
-int fsck_exists(const char *fstype);
+int fsck_exists(void);
+int fsck_exists_for_fstype(const char *fstype);
 
 /* Iterates through the path prefixes of the specified path, going up
  * the tree, to root. Also returns "" (and not "/"!) for the root

src/fsck/fsck.c

@@ -324,13 +324,21 @@ static int run(int argc, char *argv[]) {
         }
 
         if (sd_device_get_property_value(dev, "ID_FS_TYPE", &type) >= 0) {
-                r = fsck_exists(type);
+                r = fsck_exists_for_fstype(type);
                 if (r < 0)
                         log_device_warning_errno(dev, r, "Couldn't detect if fsck.%s may be used, proceeding: %m", type);
                 else if (r == 0) {
                         log_device_info(dev, "fsck.%s doesn't exist, not checking file system.", type);
                         return 0;
                 }
+        } else {
+                r = fsck_exists();
+                if (r < 0)
+                        log_device_warning_errno(dev, r, "Couldn't detect if the fsck command may be used, proceeding: %m");
+                else if (r == 0) {
+                        log_device_info(dev, "The fsck command does not exist, not checking file system.");
+                        return 0;
+                }
         }
 
         console = fopen("/dev/console", "we");

src/home/homework-luks.c

@@ -217,7 +217,7 @@ static int run_fsck(const char *node, const char *fstype) {
         assert(node);
         assert(fstype);
 
-        r = fsck_exists(fstype);
+        r = fsck_exists_for_fstype(fstype);
         if (r < 0)
                 return log_error_errno(r, "Failed to check if fsck for file system %s exists: %m", fstype);
         if (r == 0) {

src/mount/mount-tool.c

@@ -1497,7 +1497,7 @@ static int run(int argc, char* argv[]) {
                 arg_fsck = false;
 
         if (arg_fsck && arg_mount_type && arg_transport == BUS_TRANSPORT_LOCAL) {
-                r = fsck_exists(arg_mount_type);
+                r = fsck_exists_for_fstype(arg_mount_type);
                 if (r < 0)
                         log_warning_errno(r, "Couldn't determine whether fsck for %s exists, proceeding anyway.", arg_mount_type);
                 else if (r == 0) {

src/shared/dissect-image.c

@@ -1196,7 +1196,7 @@ static int run_fsck(const char *node, const char *fstype) {
         assert(node);
         assert(fstype);
 
-        r = fsck_exists(fstype);
+        r = fsck_exists_for_fstype(fstype);
         if (r < 0) {
                 log_debug_errno(r, "Couldn't determine whether fsck for %s exists, proceeding anyway.", fstype);
                 return 0;

src/shared/generator.c

@@ -167,7 +167,7 @@ int generator_write_fsck_deps(
         }
 
         if (!isempty(fstype) && !streq(fstype, "auto")) {
-                r = fsck_exists(fstype);
+                r = fsck_exists_for_fstype(fstype);
                 if (r < 0)
                         log_warning_errno(r, "Checking was requested for %s, but couldn't detect if fsck.%s may be used, proceeding: %m", what, fstype);
                 else if (r == 0) {
@@ -175,6 +175,15 @@ int generator_write_fsck_deps(
                         log_debug("Checking was requested for %s, but fsck.%s does not exist.", what, fstype);
                         return 0;
                 }
+        } else {
+                r = fsck_exists();
+                if (r < 0)
+                        log_warning_errno(r, "Checking was requested for %s, but couldn't detect if the fsck command may be used, proceeding: %m", what);
+                else if (r == 0) {
+                        /* treat missing fsck as essentially OK */
+                        log_debug("Checking was requested for %s, but the fsck command does not exist.", what);
+                        return 0;
+                }
         }
 
         if (path_equal(where, "/")) {

src/test/test-path-util.c

@@ -445,10 +445,10 @@ TEST(fsck_exists) {
         assert_se(unsetenv("PATH") == 0);
 
         /* fsck.minix is provided by util-linux and will probably exist. */
-        assert_se(fsck_exists("minix") == 1);
+        assert_se(fsck_exists_for_fstype("minix") == 1);
 
-        assert_se(fsck_exists("AbCdE") == 0);
-        assert_se(fsck_exists("/../bin/") == 0);
+        assert_se(fsck_exists_for_fstype("AbCdE") == 0);
+        assert_se(fsck_exists_for_fstype("/../bin/") == 0);
 }
 
 static void test_path_make_relative_one(const char *from, const char *to, const char *expected) {