ustar_zeropad(): Wrap strncpy() to silence GCC -Wstringop-truncation

Author: dr-m

sql/sql_backup.cc

@@ -656,6 +656,24 @@ static int backup_stream_write(IF_WIN(HANDLE, int) stream,
   return 0;
 }
 
+/**
+   Copy a prefix of a NUL terminated string to a buffer, NUL-padded.
+   @param b     output buffer
+   @param s     NUL terminated string
+   @param size  size of buf, in bytes
+*/
+static inline char *ustar_zeropad(char *b, const char *s, size_t size) noexcept
+{
+#if defined __GNUC__ && __GNUC__ >= 8
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wstringop-truncation"
+#endif
+  return strncpy(b, s, size);
+#if defined __GNUC__ && __GNUC__ >= 8
+# pragma GCC diagnostic pop
+#endif
+}
+
 /** Start streaming a file.
 @param stream   backup stream
 @param name     file name
@@ -682,14 +700,14 @@ int backup_stream_start(IF_WIN(HANDLE, int) stream,
     ustar_block_checksum(buf);
     if (int err= backup_stream_write(stream, buf, sizeof buf))
       return err;
-    const size_t whole{s & ~511U};
+    const size_t whole{s & ~(sizeof buf)};
     if (whole)
       if (int err= backup_stream_write(stream, name, whole))
         return err;
     if (s - whole)
     {
-      strncpy(buf, name + whole, 512);
-      if (int err= backup_stream_write(stream, buf, 512))
+      ustar_zeropad(buf, name + whole, sizeof buf);
+      if (int err= backup_stream_write(stream, buf, sizeof buf))
         return err;
     }
   }
@@ -726,15 +744,14 @@ extern "C" int backup_stream_config(IF_WIN(HANDLE, int) stream,
   if (int ret=
       backup_stream_start(stream, "backup.cnf", 0644, size, nullptr, 0))
     return ret;
-  const size_t whole{size & ~511U};
+  char buf[512];
+  const size_t whole{size & ~(sizeof buf)};
   if (whole)
     if (int err= backup_stream_write(stream, config, whole))
       return err;
   if (size == whole)
     return 0;
-
-  char buf[512];
-  strncpy(buf, config + whole, sizeof buf);
+  ustar_zeropad(buf, config + whole, sizeof buf);
   return backup_stream_write(stream, buf, sizeof buf);
 }