record: Fix crash when the root is not existed

This patch to fix crash when the root is not existed, due to some embed
devices maybe not have it

Signed-off-by: yuxuan zhou <zyxeeker@gmail.com>

cmds/record.c

@@ -942,16 +942,24 @@ static void unlink_shmem_list(void)
 		sscanf(sl->id, "/uftrace-%[^-]-%*d-%*d", shmem_session);
 		pr_dbg2("unlink for session: %s\n", shmem_session);
 
-		num = scandir(uftrace_shmem_root(), &shmem_bufs, filter_shmem, alphasort);
-		for (i = 0; i < num; i++) {
-			sid[0] = '/';
-			memcpy(&sid[1], shmem_bufs[i]->d_name, MSG_ID_SIZE);
-			pr_dbg3("unlink %s\n", sid);
-			uftrace_shmem_unlink(sid);
-			free(shmem_bufs[i]);
+		/* check the root is existed (due to some embed devices maybe not have it) */
+		if (access(uftrace_shmem_root(), F_OK) == 0) {
+			num = scandir(uftrace_shmem_root(), &shmem_bufs, filter_shmem, alphasort);
+			for (i = 0; i < num; i++) {
+				sid[0] = '/';
+				memcpy(&sid[1], shmem_bufs[i]->d_name, MSG_ID_SIZE);
+				pr_dbg3("unlink %s\n", sid);
+				uftrace_shmem_unlink(sid);
+				free(shmem_bufs[i]);
+			}
+
+			free(shmem_bufs);
+		}
+		else {
+			pr_dbg2("access %s failed, err: %s\n", uftrace_shmem_root(),
+				strerror(errno));
 		}
 
-		free(shmem_bufs);
 		free(sl);
 	}
 }