skip msync() if nothing was changed

vanilla-dpup · Sep 30, 2024 · d81c913 · d81c913
1 parent b7217b2
commit d81c913
Showing 1 changed file with 8 additions and 4 deletions.
diff --git a/woof-code/rootfs-petbuilds/psnapcp/psnapcp.c b/woof-code/rootfs-petbuilds/psnapcp/psnapcp.c
@@ -12,7 +12,7 @@
 
 int main(int argc, char *argv[])
 {
-	int src, dst;
+	int src, dst, sync = 0;
 	struct stat srcstat, dststat;
 	struct timeval times[2];
 	unsigned char *srcm, *dstm;
@@ -75,22 +75,26 @@ int main(int argc, char *argv[])
 	madvise(srcm, srcstat.st_size, MADV_SEQUENTIAL);
 	madvise(dstm, srcstat.st_size, MADV_SEQUENTIAL);
 
-	if (srcstat.st_size > 0 && dststat.st_size == 0)
+	if (srcstat.st_size > 0 && dststat.st_size == 0) {
 		memcpy(dstm, srcm, srcstat.st_size);
+		sync = 1;
+	}
 	else {
 		do {
 			chunk = srcstat.st_size - off >= CHUNK_SIZE ? CHUNK_SIZE : srcstat.st_size - off;
 
-			if (memcmp(&srcm[off], &dstm[off], chunk) != 0)
+			if (memcmp(&srcm[off], &dstm[off], chunk) != 0) {
 				memcpy(&dstm[off], &srcm[off], chunk);
+				sync = 1;
+			}
 
 			off += chunk;
 		} while (off < srcstat.st_size);
 	}
 
 	munmap(srcm, srcstat.st_size);
 
-	if (msync(dstm, srcstat.st_size, MS_SYNC) < 0) {
+	if (sync && msync(dstm, srcstat.st_size, MS_SYNC) < 0) {
 		fprintf(stderr, "Failed to flush changes to disk: %s\n", strerror(errno));
 		munmap(dstm, srcstat.st_size);
 		close(dst);