Scramble default write buffer contents slightly

[fio.git] / io_u.c

diff --git a/io_u.c b/io_u.c
index a87c58e32791e35cfbb770c705a2c34c9b41ee17..af2d05f360eaed2f4d6c169f6ee5eb5f62da18f8 100644 (file)
--- a/io_u.c
+++ b/io_u.c
@@ -1120,6 +1120,19 @@ static int check_get_verify(struct thread_data *td, struct io_u *io_u)
        return 0;
 }
 
+/*
+ * Fill offset and start time into the buffer content, to prevent too
+ * easy compressible data for simple de-dupe attempts.
+ */
+static void small_content_scramble(struct io_u *io_u)
+{
+       void *end;
+
+       *((unsigned long long *) io_u->xfer_buf) = io_u->offset;
+       end = io_u->xfer_buf + io_u->xfer_buflen - sizeof(io_u->start_time);
+       memcpy(end, &io_u->start_time, sizeof(io_u->start_time));
+}
+
 /*
  * Return an io_u to be processed. Gets a buflen and offset, sets direction,
  * etc. The returned io_u is fully ready to be prepped and submitted.
@@ -1128,6 +1141,7 @@ struct io_u *get_io_u(struct thread_data *td)
 {
        struct fio_file *f;
        struct io_u *io_u;
+       int do_scramble = 0;
 
        io_u = __get_io_u(td);
        if (!io_u) {
@@ -1173,6 +1187,8 @@ struct io_u *get_io_u(struct thread_data *td)
                        populate_verify_io_u(td, io_u);
                else if (td->o.refill_buffers && io_u->ddir == DDIR_WRITE)
                        io_u_fill_buffer(td, io_u, io_u->xfer_buflen);
+               else if (io_u->ddir == DDIR_WRITE)
+                       do_scramble = 1;
                else if (io_u->ddir == DDIR_READ) {
                        /*
                         * Reset the buf_filled parameters so next time if the
@@ -1193,6 +1209,8 @@ out:
        if (!td_io_prep(td, io_u)) {
                if (!td->o.disable_slat)
                        fio_gettime(&io_u->start_time, NULL);
+               if (do_scramble)
+                       small_content_scramble(io_u);
                return io_u;
        }
 err_put: