svn commit: r282131 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Andriy Gapon]

Author: avg
Date: Tue Apr 28 09:19:40 2015
New Revision: 282131
URL: https://svnweb.freebsd.org/changeset/base/282131

Log:
  replace a comment about zfs recv -F corner case with a longer, more detailed one
  
  The old comment in zfs_rezget explains what situation the code handles,
  the new comment also describes how the situation can arise.
  
  Also, re-join a line that became sufficiently shorti some time ago.
  
  Differential Revision:	https://reviews.freebsd.org/D2352
  Reviewed by:	delphij, smh
  MFC after:	12 days

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c	Tue Apr 28 09:11:47 2015	(r282130)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c	Tue Apr 28 09:19:40 2015	(r282131)
@@ -1320,15 +1320,25 @@ zfs_rezget(znode_t *zp)
 	}
 
 	/*
-	 * XXXPJD: Not sure how is that possible, but under heavy
-	 * zfs recv -F load it happens that z_gen is the same, but
-	 * vnode type is different than znode type. This would mean
-	 * that for example regular file was replaced with directory
-	 * which has the same object number.
+	 * It is highly improbable but still quite possible that two
+	 * objects in different datasets are created with the same
+	 * object numbers and in transaction groups with the same
+	 * numbers.  znodes corresponding to those objects would
+	 * have the same z_id and z_gen, but their other attributes
+	 * may be different.
+	 * zfs recv -F may replace one of such objects with the other.
+	 * As a result file properties recorded in the replaced
+	 * object's vnode may no longer match the received object's
+	 * properties.  At present the only cached property is the
+	 * files type recorded in v_type.
+	 * So, handle this case by leaving the old vnode and znode
+	 * disassociated from the actual object.  A new vnode and a
+	 * znode will be created if the object is accessed
+	 * (e.g. via a look-up).  The old vnode and znode will be
+	 * recycled when the last vnode reference is dropped.
 	 */
 	vp = ZTOV(zp);
-	if (vp != NULL &&
-	    vp->v_type != IFTOVT((mode_t)zp->z_mode)) {
+	if (vp != NULL && vp->v_type != IFTOVT((mode_t)zp->z_mode)) {
 		zfs_znode_dmu_fini(zp);
 		ZFS_OBJ_HOLD_EXIT(zfsvfs, obj_num);
 		return (EIO);