svn commit: r297506 - vendor-sys/illumos/dist/uts/common/fs/zfs

[Alexander Motin]

Author: mav
Date: Sat Apr  2 08:25:41 2016
New Revision: 297506
URL: https://svnweb.freebsd.org/changeset/base/297506

Log:
  6738 zfs send stream padding needs documentation
  
  Reviewed by: Matthew Ahrens <mahrens at delphix.com>
  Reviewed by: Dan Kimmel <dan.kimmel at delphix.com>
  Reviewed by: Paul Dagnelie <pcd at delphix.com>
  Reviewed by: Dan McDonald <danmcd at omniti.com>
  Approved by: Robert Mustacchi <rm at joyent.com>
  Author: Eli Rosenthal <eli.rosenthal at delphix.com>
  
  illumos/illumos-gate at c20404ff77119516354b0d112d28b7ea0dadd303

Modified:
  vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_send.c

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_send.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_send.c	Sat Apr  2 08:24:23 2016	(r297505)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_send.c	Sat Apr  2 08:25:41 2016	(r297506)
@@ -96,6 +96,19 @@ dump_bytes(dmu_sendarg_t *dsp, void *buf
 {
 	dsl_dataset_t *ds = dmu_objset_ds(dsp->dsa_os);
 	ssize_t resid; /* have to get resid to get detailed errno */
+
+	/*
+	 * The code does not rely on this (len being a multiple of 8).  We keep
+	 * this assertion because of the corresponding assertion in
+	 * receive_read().  Keeping this assertion ensures that we do not
+	 * inadvertently break backwards compatibility (causing the assertion
+	 * in receive_read() to trigger on old software).
+	 *
+	 * Removing the assertions could be rolled into a new feature that uses
+	 * data that isn't 8-byte aligned; if the assertions were removed, a
+	 * feature flag would have to be added.
+	 */
+
 	ASSERT0(len % 8);
 
 	dsp->dsa_err = vn_rdwr(UIO_WRITE, dsp->dsa_vp,
@@ -1758,7 +1771,10 @@ receive_read(struct receive_arg *ra, int
 {
 	int done = 0;
 
-	/* some things will require 8-byte alignment, so everything must */
+	/*
+	 * The code doesn't rely on this (lengths being multiples of 8).  See
+	 * comment in dump_bytes.
+	 */
 	ASSERT0(len % 8);
 
 	while (done < len) {