X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=io_u.c;h=77069c55277f8aeb0cd93d99754b12913cdfbaee;hp=af2d05f360eaed2f4d6c169f6ee5eb5f62da18f8;hb=b1d1b239d2a3299a4d7b7b3de185923c655d0a48;hpb=de78976982fe7f57ccadd15a19dae167f0ce62ab

diff --git a/io_u.c b/io_u.c
index af2d05f3..77069c55 100644
--- a/io_u.c
+++ b/io_u.c
@@ -1122,15 +1122,40 @@ static int check_get_verify(struct thread_data *td, struct io_u *io_u)
 
 /*
  * Fill offset and start time into the buffer content, to prevent too
- * easy compressible data for simple de-dupe attempts.
+ * easy compressible data for simple de-dupe attempts. Do this for every
+ * 512b block in the range, since that should be the smallest block size
+ * we can expect from a device.
  */
 static void small_content_scramble(struct io_u *io_u)
 {
-	void *end;
+	unsigned int i, nr_blocks = io_u->buflen / 512;
+	unsigned long long boffset;
+	unsigned int offset;
+	void *p, *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));
+	if (!nr_blocks)
+		return;
+
+	p = io_u->xfer_buf;
+	boffset = io_u->offset;
+
+	for (i = 0; i < nr_blocks; i++) {
+		/*
+		 * Fill the byte offset into a "random" start offset of
+		 * the buffer, given by the product of the usec time
+		 * and the actual offset.
+		 */
+		offset = (io_u->start_time.tv_usec ^ boffset) & 511;
+		offset &= ~(sizeof(unsigned long long) - 1);
+		if (offset >= 512 - sizeof(unsigned long long))
+			offset -= sizeof(unsigned long long);
+		memcpy(p + offset, &boffset, sizeof(boffset));
+
+		end = p + 512 - sizeof(io_u->start_time);
+		memcpy(end, &io_u->start_time, sizeof(io_u->start_time));
+		p += 512;
+		boffset += 512;
+	}
 }
 
 /*
@@ -1183,13 +1208,14 @@ struct io_u *get_io_u(struct thread_data *td)
 		f->last_start = io_u->offset;
 		f->last_pos = io_u->offset + io_u->buflen;
 
-		if (td->o.verify != VERIFY_NONE && io_u->ddir == DDIR_WRITE)
-			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) {
+		if (io_u->ddir == DDIR_WRITE) {
+			if (td->o.verify != VERIFY_NONE)
+				populate_verify_io_u(td, io_u);
+			else if (td->o.refill_buffers)
+				io_u_fill_buffer(td, io_u, io_u->xfer_buflen);
+			else if (td->o.scramble_buffers)
+				do_scramble = 1;
+		} else if (io_u->ddir == DDIR_READ) {
 			/*
 			 * Reset the buf_filled parameters so next time if the
 			 * buffer is used for writes it is refilled.