Illumos 4390 - I/O errors can corrupt space map when deleting fs/vol

4390 i/o errors when deleting filesystem/zvol can lead to space map corruption
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Approved by: Dan McDonald <danmcd@omniti.com>

References:
  https://www.illumos.org/issues/4390
  https://github.com/illumos/illumos-gate/commit/7fd05ac

Porting notes:

Previous stack-reduction efforts in traverse_visitb() caused a fair
number of un-mergable pieces of code.  This patch should reduce its
stack footprint a bit more.

The new local bptree_entry_phys_t in bptree_add() is dynamically-allocated
using kmem_zalloc() for the purpose of stack reduction.

The new global zfs_free_leak_on_eio has been defined as an integer
rather than a boolean_t as was the case with the related zfs_recover
global.  Also, zfs_free_leak_on_eio's definition has been inserted into
zfs_debug.c for consistency with the existing definition of zfs_recover.
Illumos placed it in spa_misc.c.

Ported by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2545

include/sys/bptree.h

@@ -19,7 +19,7 @@
  * CDDL HEADER END
  */
 /*
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  */
 
 #ifndef	_SYS_BPTREE_H
@@ -50,6 +50,7 @@ typedef int bptree_itor_t(void *arg, const blkptr_t *bp, dmu_tx_t *tx);
 
 uint64_t bptree_alloc(objset_t *os, dmu_tx_t *tx);
 int bptree_free(objset_t *os, uint64_t obj, dmu_tx_t *tx);
+boolean_t bptree_is_empty(objset_t *os, uint64_t obj);
 
 void bptree_add(objset_t *os, uint64_t obj, blkptr_t *bp, uint64_t birth_txg,
     uint64_t bytes, uint64_t comp, uint64_t uncomp, dmu_tx_t *tx);