From f95478f1f146eef1615504ea425412580eb1eff5 Mon Sep 17 00:00:00 2001
From: LoveSy <shana@zju.edu.cn>
Date: Sun, 21 May 2023 12:09:20 +0800
Subject: [PATCH] Truncate file only if needed

---
 native/src/sepolicy/policydb.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/native/src/sepolicy/policydb.cpp b/native/src/sepolicy/policydb.cpp
index 540990616..b6525cbcb 100644
--- a/native/src/sepolicy/policydb.cpp
+++ b/native/src/sepolicy/policydb.cpp
@@ -248,9 +248,12 @@ bool sepolicy::to_file(const char *file) {
         return false;
     }
 
-    int fd = xopen(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
+    int fd = xopen(file, O_WRONLY | O_CREAT | O_CLOEXEC, 0644);
     if (fd < 0)
         return false;
+    if (struct stat st{}; xfstat(fd, &st) == 0 && st.st_size > 0) {
+        ftruncate(fd, 0);
+    }
     xwrite(fd, data.buf, data.sz);
 
     close(fd);