fs: Reserve place for task's root dumping

Do not restore it yet -- the logic we're about to apply to
resolve tasks' paths relative to dumper/restorer is not yet
clear to me and it should better be hidden into a couple of
calls (dump_one_reg_file/open_fe_fd). But since we can't
chroot to fd we're about to expose the logic outside of the
open_fe_fd, which is not desirable ATM.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -494,13 +494,35 @@ static int dump_task_fs(pid_t pid, struct cr_fdset *fdset)
 	fe.cwd_id = fd_id_generate_special();
 
 	ret = dump_one_reg_file(fd, fe.cwd_id, &p);
-	if (!ret) {
-		pr_info("Dumping task cwd id %x\n", fe.cwd_id);
-		ret = write_img(fdset_fd(fdset, CR_FD_FS), &fe);
+	if (ret < 0)
+		return ret;
+
+	close(fd);
+
+	fd = open_proc(pid, "root");
+	if (fd < 0)
+		return -1;
+
+	if (fstat(fd, &p.stat) < 0) {
+		pr_perror("Can't stat root");
+		return -1;
 	}
 
+	p.type = FDINFO_REG;
+	p.flags = 0;
+	p.pos = 0;
+	fe.root_id = fd_id_generate_special();
+
+	ret = dump_one_reg_file(fd, fe.root_id, &p);
+	if (ret < 0)
+		return ret;
+
 	close(fd);
-	return ret;
+
+	pr_info("Dumping task cwd id %x root id %x\n",
+			fe.cwd_id, fe.root_id);
+
+	return write_img(fdset_fd(fdset, CR_FD_FS), &fe);
 }
 
 struct shmem_info

cr-show.c

@@ -177,8 +177,10 @@ void show_fs(int fd_fs, struct cr_options *o)
 
 	pr_img_head(CR_FD_FS);
 
-	if (read_img(fd_fs, &fe) > 0)
-		pr_msg("CWD: %x\n", fe.cwd_id);
+	if (read_img(fd_fs, &fe) > 0) {
+		pr_msg("CWD : %x\n", fe.cwd_id);
+		pr_msg("ROOT: %x\n", fe.root_id);
+	}
 
 	pr_img_tail(CR_FD_FS);
 }

files.c

@@ -563,6 +563,15 @@ int prepare_fs(int pid)
 	close(cwd);
 	close(ifd);
 
+	/*
+	 * FIXME: restore task's root. Don't want to do it now, since
+	 * it's not yet clean how we're going to resolve tasks' paths
+	 * relative to the dumper/restorer and all this logic is likely
+	 * to be hidden in a couple of calls (open_fe_fd is one od them)
+	 * but for chroot there's no fchroot call, we have to chroot
+	 * by path thus exposing this (yet unclean) logic here.
+	 */
+
 	return 0;
 }
 

include/image.h

@@ -65,6 +65,7 @@ struct fdinfo_entry {
 
 struct fs_entry {
 	u32	cwd_id;
+	u32	root_id;
 } __packed;
 
 struct pstree_entry {