fastrpc: hexagonrpcd: hexagonfs: add optionally mapped directories

Some directories are not required for the normal operation of the sensor
firmware, such as the sensor configuration directory. Add support for
directories that are empty if they are not present in the physical
filesystem.

fastrpc/hexagonrpcd/hexagonfs.h

@@ -64,6 +64,7 @@ struct hexagonfs_fd {
 };
 
 extern struct hexagonfs_file_ops hexagonfs_mapped_ops;
+extern struct hexagonfs_file_ops hexagonfs_mapped_or_empty_ops;
 extern struct hexagonfs_file_ops hexagonfs_mapped_sysfs_ops;
 extern struct hexagonfs_file_ops hexagonfs_plat_subtype_name_ops;
 extern struct hexagonfs_file_ops hexagonfs_virt_dir_ops;

fastrpc/hexagonrpcd/hexagonfs_mapped.c

@@ -215,6 +215,89 @@ static int mapped_stat(struct hexagonfs_fd *fd, struct stat *stats)
 	return 0;
 }
 
+static void mapped_or_empty_close(void *fd_data)
+{
+	if (fd_data)
+		mapped_close(fd_data);
+}
+
+static int mapped_or_empty_from_dirent(void *dirent_data, bool dir, void **fd_data)
+{
+	int ret;
+
+	ret = mapped_from_dirent(dirent_data, dir, fd_data);
+	if (ret)
+		fd_data = NULL;
+
+	return 0;
+}
+
+static int mapped_or_empty_openat(struct hexagonfs_fd *dir,
+				  const char *segment,
+				  bool expect_dir,
+				  struct hexagonfs_fd **out)
+{
+	if (dir->data)
+		return mapped_openat(dir, segment, expect_dir, out);
+	else
+		return -ENOENT;
+}
+
+static ssize_t mapped_or_empty_read(struct hexagonfs_fd *fd,
+				    size_t size, void *out)
+{
+	if (fd->data)
+		return mapped_read(fd, size, out);
+
+	return 0;
+}
+
+static int mapped_or_empty_readdir(struct hexagonfs_fd *fd,
+				   size_t size, char *out)
+{
+	if (fd->data) {
+		return mapped_readdir(fd, size, out);
+	} else {
+		out[0] = '\0';
+		return 0;
+	}
+}
+
+static int mapped_or_empty_seek(struct hexagonfs_fd *fd, off_t off, int whence)
+{
+	if (fd->data)
+		return mapped_seek(fd, off, whence);
+	else
+		return 0;
+}
+
+static int mapped_or_empty_stat(struct hexagonfs_fd *fd, struct stat *stats)
+{
+	if (fd->data) {
+		return mapped_stat(fd, stats);
+	} else {
+		stats->st_size = 0;
+		stats->st_dev = 0;
+		stats->st_rdev = 0;
+		stats->st_ino = 0;
+		stats->st_nlink = 0;
+
+		stats->st_mode = S_IFDIR
+			       | S_IRUSR | S_IXUSR
+			       | S_IRGRP | S_IXGRP
+			       | S_IROTH | S_IXOTH;
+
+		stats->st_atim.tv_sec = 0;
+		stats->st_atim.tv_nsec = 0;
+		stats->st_ctim.tv_sec = 0;
+		stats->st_ctim.tv_nsec = 0;
+		stats->st_mtim.tv_sec = 0;
+		stats->st_mtim.tv_nsec = 0;
+
+		return 0;
+	}
+}
+
 /*
  * This is the sysfs variant of the stat function.
  *
@@ -248,6 +331,16 @@ struct hexagonfs_file_ops hexagonfs_mapped_ops = {
 	.stat = mapped_stat,
 };
 
+struct hexagonfs_file_ops hexagonfs_mapped_or_empty_ops = {
+	.close = mapped_or_empty_close,
+	.from_dirent = mapped_or_empty_from_dirent,
+	.openat = mapped_or_empty_openat,
+	.read = mapped_or_empty_read,
+	.readdir = mapped_or_empty_readdir,
+	.seek = mapped_or_empty_seek,
+	.stat = mapped_or_empty_stat,
+};
+
 struct hexagonfs_file_ops hexagonfs_mapped_sysfs_ops = {
 	.close = mapped_close,
 	.from_dirent = mapped_from_dirent,