fileio: teach read_one_line_file_at() XAT_FDROOT support

src/basic/fileio.c

@@ -420,11 +420,11 @@ int read_one_line_file_at(int dir_fd, const char *filename, char **ret) {
         _cleanup_fclose_ FILE *f = NULL;
         int r;
 
-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
         assert(filename);
         assert(ret);
 
-        r = fopen_unlocked_at(dir_fd, filename, "re", 0, &f);
+        r = fopen_unlocked_at(dir_fd, filename, "re", /* open_flags= */ 0, &f);
         if (r < 0)
                 return r;
 
@@ -1010,13 +1010,19 @@ static int xfopenat_regular(int dir_fd, const char *path, const char *mode, int
 
         /* A combination of fopen() with openat() */
 
-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
         assert(mode);
         assert(ret);
 
         if (dir_fd == AT_FDCWD && path && open_flags == 0)
                 f = fopen(path, mode);
-        else {
+        else if (dir_fd == XAT_FDROOT && path && open_flags == 0) {
+                _cleanup_free_ char *j = strjoin("/", path);
+                if (!j)
+                        return -ENOMEM;
+
+                f = fopen(j, mode);
+        } else {
                 _cleanup_close_ int fd = -EBADF;
                 int mode_flags;
 
@@ -1051,7 +1057,7 @@ static int xfopenat_unix_socket(int dir_fd, const char *path, const char *bind_n
         FILE *f;
         int r;
 
-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
         assert(ret);
 
         sk = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
@@ -1099,7 +1105,7 @@ int xfopenat_full(
         FILE *f = NULL;  /* avoid false maybe-uninitialized warning */
         int r;
 
-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
         assert(mode);
         assert(ret);
 

src/basic/socket-util.c

@@ -1619,13 +1619,17 @@ int connect_unix_path(int fd, int dir_fd, const char *path) {
         _cleanup_close_ int inode_fd = -EBADF;
 
         assert(fd >= 0);
-        assert(dir_fd == AT_FDCWD || dir_fd >= 0);
+        assert(IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT) || dir_fd >= 0);
 
         /* Connects to the specified AF_UNIX socket in the file system. Works around the 108 byte size limit
          * in sockaddr_un, by going via O_PATH if needed. This hence works for any kind of path. */
 
-        if (!path)
+        if (!path) {
+                if (dir_fd < 0)
+                        return -EISDIR;
+
                 return connect_unix_inode(fd, dir_fd); /* If no path is specified, then dir_fd refers to the socket inode to connect to. */
+        }
 
         /* Refuse zero length path early, to make sure AF_UNIX stack won't mistake this for an abstract
          * namespace path, since first char is NUL */
@@ -1640,7 +1644,14 @@ int connect_unix_path(int fd, int dir_fd, const char *path) {
          * exist. If the path is too long, we also need to take the indirect route, since we can't fit this
          * into a sockaddr_un directly. */
 
-        inode_fd = openat(dir_fd, path, O_PATH|O_CLOEXEC);
+        if (dir_fd == XAT_FDROOT) {
+                _cleanup_free_ char *j = strjoin("/", path);
+                if (!j)
+                        return -ENOMEM;
+
+                inode_fd = open(j, O_PATH|O_CLOEXEC);
+        } else
+                inode_fd = openat(dir_fd, path, O_PATH|O_CLOEXEC);
         if (inode_fd < 0)
                 return -errno;