[Sheepdog] panic in get_nth_node

[huxinwei]

Hi Yuan,
  I did reproduce the issue yesterday. Here's the related log:

Mar 14 22:33:01 request_obj_list(1702) 30064771072002
Mar 14 22:33:01 screen_obj_list(1745) 2
Mar 14 22:33:01 fill_obj_list(1814) 2
Mar 14 22:33:01 recover_object(1479) done:0 count:2, oid:71d60700000000
Mar 14 22:33:01 err_to_sderr(118) object 0071d60700000000 not found locally
Mar 14 22:33:01 do_recover_object(1412) try recover object 71d60700000000 from epoch 36
Mar 14 22:33:01 find_tgt_node(1195) 34, 64, 1, 67, 128, 2, 1
Mar 14 22:33:01 recover_object_from_replica(1318) 192.168.136.130, 7000
Mar 14 22:33:01 recover_object_from_replica(1361) failed, res: 2
Mar 14 22:33:01 do_recover_object(1412) try recover object 71d60700000000 from epoch 35
Mar 14 22:33:01 find_tgt_node(1195) 67, 128, 2, 34, 64, 1, 1
Mar 14 22:33:01 get_nth_node(193) bug
Mar 14 22:33:01 log_sigexit(361) sheep pid 17851 exiting.

  I think I figured out what's wrong this time. So here's an new patch obsolete the previous one.
Would you help to review it ?

It can be cases that, in some epoch, sheepdog cannot maintain the required copies of replications.
When recovering from such epoch, we'd better be conservative and double check.

Signed-off-by: Xinwei Hu <huxinwei at huawei.com>
---
 sheep/store.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/sheep/store.c b/sheep/store.c
index 9f8a2c6..b875bc5 100644
--- a/sheep/store.c
+++ b/sheep/store.c
@@ -1326,6 +1326,13 @@ again:

        dprintf("try recover object %"PRIx64" from epoch %"PRIu32"\n", oid, tgt_epoch);

+       if (cur_copies <= copy_idx) {
+               eprintf("epoch (%d) has less copies (%d) than requested copy_idx: %d\n",
+                               tgt_epoch, cur_copies, copy_idx);
+               ret = -1;
+               goto err;
+       }
+
        tgt_idx = find_tgt_node(old, old_nr, old_idx, old_copies,
                        cur, cur_nr, cur_idx, cur_copies, copy_idx);
        if (tgt_idx < 0) {
--
1.7.1