Make rename properly atomic

2 files changed, 20 insertions, 4 deletions

diff --git a/automedia b/automedia
index 5f5eb0c..3885e0d 100755
--- a/automedia
+++ b/automedia
diff --git a/src/fileutils.c b/src/fileutils.c
index 72d9c29..d7021dc 100644
--- a/src/fileutils.c
+++ b/src/fileutils.c
@@ -180,11 +180,27 @@ int file_overwrite_in_dir(const char *dir, const char *filename, const char *dat
     strcpy(tmp_filepath, filepath);
     strcpy(tmp_filepath + filepath_len, ".tmp");
 
-    int result = file_overwrite(tmp_filepath, data, size);
-    if(result != 0)
-        return result;
+    int fd = open(tmp_filepath, O_CREAT | O_WRONLY, 0666);
+    if(fd == -1) {
+        perror(filepath);
+        return -1;
+    }
+
+    ssize_t bytes_written = write(fd, data, size);
+    if(bytes_written != (ssize_t)size) {
+        fprintf(stderr, "Failed to write all bytes to file %s. Expected to write %zu bytes, only wrote %zd bytes\n", filepath, size, bytes_written);
+        close(fd);
+        return -1;
+    }
+
+    if(fsync(fd) == -1) {
+        perror(filepath);
+        close(fd);
+        return -1;
+    }
 
-    /* Rename is atomic! */
+    close(fd);
+    /* fsync + rename is atomic! */
     return rename(tmp_filepath, filepath);
 }