stat-util: introduce a common (stat|fd)_verify_regular_or_block() helper

We already had one in repart.c, let's generalize it, and use it
everywhere.

src/basic/stat-util.c

@@ -220,6 +220,28 @@ int is_device_node(const char *path) {
         return verify_stat_at(AT_FDCWD, path, false, stat_verify_device_node, false);
 }
 
+int stat_verify_regular_or_block(const struct stat *st) {
+        assert(st);
+
+        if (S_ISDIR(st->st_mode))
+                return -EISDIR;
+
+        if (S_ISLNK(st->st_mode))
+                return -ELOOP;
+
+        if (!S_ISREG(st->st_mode) && !S_ISBLK(st->st_mode))
+                return -EBADFD;
+
+        return 0;
+}
+
+int fd_verify_regular_or_block(int fd) {
+        if (IN_SET(fd, AT_FDCWD, XAT_FDROOT))
+                return -EISDIR;
+
+        return verify_stat_at(fd, /* path= */ NULL, /* follow= */ false, stat_verify_regular_or_block, /* verify= */ true);
+}
+
 int dir_is_empty_at(int dir_fd, const char *path, bool ignore_hidden_or_backup) {
         _cleanup_close_ int fd = -EBADF;
         struct dirent *buf;

src/basic/stat-util.h

@@ -31,6 +31,9 @@ int fd_verify_linked(int fd);
 int stat_verify_device_node(const struct stat *st);
 int is_device_node(const char *path);
 
+int stat_verify_regular_or_block(const struct stat *st);
+int fd_verify_regular_or_block(int fd);
+
 int dir_is_empty_at(int dir_fd, const char *path, bool ignore_hidden_or_backup);
 static inline int dir_is_empty(const char *path, bool ignore_hidden_or_backup) {
         return dir_is_empty_at(AT_FDCWD, path, ignore_hidden_or_backup);