Fix ENOSPC in "Handle zap_add() failures in ..."

Commit cc63068 caused ENOSPC error when copy a large amount of files
between two directories. The reason is that the patch limits zap leaf
expansion to 2 retries, and return ENOSPC when failed.

The intent for limiting retries is to prevent pointlessly growing table
to max size when adding a block full of entries with same name in
different case in mixed mode. However, it turns out we cannot use any
limit on the retry. When we copy files from one directory in readdir
order, we are copying in hash order, one leaf block at a time. Which
means that if the leaf block in source directory has expanded 6 times,
and you copy those entries in that block, by the time you need to expand
the leaf in destination directory, you need to expand it 6 times in one
go. So any limit on the retry will result in error where it shouldn't.

Note that while we do use different salt for different directories, it
seems that the salt/hash function doesn't provide enough randomization
to the hash distance to prevent this from happening.

Since cc63068 has already been reverted. This patch adds it back and
removes the retry limit.

Also, as it turn out, failing on zap_add() has a serious side effect for
mzap_upgrade(). When upgrading from micro zap to fat zap, it will
call zap_add() to transfer entries one at a time. If it hit any error
halfway through, the remaining entries will be lost, causing those files
to become orphan. This patch add a VERIFY to catch it.

Reviewed-by: Sanjeev Bagewadi <[email protected]>
Reviewed-by: Richard Yao <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Reviewed-by: Albert Lee <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Signed-off-by: Chunwei Chen <[email protected]>
Closes #7401 
Closes #7421 

1 files changed, 11 insertions, 4 deletions

diff --git a/include/sys/zap_leaf.h b/include/sys/zap_leaf.h
index e784c5963..a3da1036a 100644
--- a/include/sys/zap_leaf.h
+++ b/include/sys/zap_leaf.h
@@ -46,10 +46,15 @@ struct zap_stats;
  * block size (1<<l->l_bs) - hash entry size (2) * number of hash
  * entries - header space (2*chunksize)
  */
-#define	ZAP_LEAF_NUMCHUNKS(l) \
-	(((1<<(l)->l_bs) - 2*ZAP_LEAF_HASH_NUMENTRIES(l)) / \
+#define	ZAP_LEAF_NUMCHUNKS_BS(bs) \
+	(((1<<(bs)) - 2*ZAP_LEAF_HASH_NUMENTRIES_BS(bs)) / \
 	ZAP_LEAF_CHUNKSIZE - 2)
 
+#define	ZAP_LEAF_NUMCHUNKS(l) (ZAP_LEAF_NUMCHUNKS_BS(((l)->l_bs)))
+
+#define	ZAP_LEAF_NUMCHUNKS_DEF \
+	(ZAP_LEAF_NUMCHUNKS_BS(fzap_default_block_shift))
+
 /*
  * The amount of space within the chunk available for the array is:
  * chunk size - space for type (1) - space for next pointer (2)
@@ -74,8 +79,10 @@ struct zap_stats;
  * which is less than block size / CHUNKSIZE (24) / minimum number of
  * chunks per entry (3).
  */
-#define	ZAP_LEAF_HASH_SHIFT(l) ((l)->l_bs - 5)
-#define	ZAP_LEAF_HASH_NUMENTRIES(l) (1 << ZAP_LEAF_HASH_SHIFT(l))
+#define	ZAP_LEAF_HASH_SHIFT_BS(bs) ((bs) - 5)
+#define	ZAP_LEAF_HASH_NUMENTRIES_BS(bs) (1 << ZAP_LEAF_HASH_SHIFT_BS(bs))
+#define	ZAP_LEAF_HASH_SHIFT(l) (ZAP_LEAF_HASH_SHIFT_BS(((l)->l_bs)))
+#define	ZAP_LEAF_HASH_NUMENTRIES(l) (ZAP_LEAF_HASH_NUMENTRIES_BS(((l)->l_bs)))
 
 /*
  * The chunks start immediately after the hash table.  The end of the