[Nbd] [PATCH] nbd-tester-client: analyse bad data using hash function huersistic

[Alex Bligh <alex@...872...>]

The hash function used by the integrity test was designed specifically
such that with < (2^32) blocks and < (2^32) read/write operations, it
can accurately guess how the bad data returned was generated. This
patch uses this huersistic to provide a guess as to what is wrong.
EG if it prints out a correct block number but a bad sequence number,
it is likely the server is disordering writes or has missed writes.

Available from git.alex.org.uk as usual.

Signed-off-by: Alex Bligh <alex@...872...>
---
 nbd-tester-client.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/nbd-tester-client.c b/nbd-tester-client.c
index f2ebffc..9e85c83 100644
--- a/nbd-tester-client.c
+++ b/nbd-tester-client.c
@@ -1087,7 +1087,12 @@ int integrity_test(gchar* hostname, int port, char* name, int sock,
 					if (checkbuf(dbuf, blkhash[blknum], blknum))
 					{
 						retval=-1;
-						snprintf(errstr, errstr_len, "Bad reply data: seq %08x", blkhash[blknum]);
+						snprintf(errstr, errstr_len, "Bad reply data: I wanted blk %08x, seq %08x but I got (at a guess) blk %08x, seq %08x",
+							 (unsigned int) blknum,
+							 blkhash[blknum],
+							 ((uint32_t *)(dbuf))[0],
+							 ((uint32_t *)(dbuf))[1]
+							 );
 						goto err_open;
 						
 					}
-- 
1.7.4.1