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Description of problem:
--discards doesn't work with lvcreate and the default is ignore not passdown.

Version-Release number of selected component (if applicable):
lvm2-2.02.97-1.el7.x86_64

How reproducible:


Steps to Reproduce:
1. man lvcreate
===
       --discards {ignore|nopassdown|passdown}
              Set discards behavior.  Default is passdown.
===

2. create thin pool with --discards
# lvcreate -L16m -T tsvg/pool1 
# lvcreate -L16m -T tsvg/pool2 --discards nopassdown

3. # lvs -ovg_name,lv_name,discards tsvg
  VG   LV    Discards
  tsvg pool1   ignore
  tsvg pool2   ignore
  
# dmsetup table --target thin-pool
tsvg-pool1-tpool: 0 32768 thin-pool 253:1 253:2 128 0 1 ignore_discard 
tsvg-pool2-tpool: 0 32768 thin-pool 253:5 253:6 128 0 1 ignore_discard 

from the debug log:
===
#lvmcmdline.c:1087         Processing: lvcreate -L16m -T tsvg/pool3 --discards nopassdown -vvvv
>>>snip>>>
#libdm-deptree.c:2324         Adding target to (253:12): 0 32768 thin-pool 253:10 253:11 128 0 1 ignore_discard
===

Actual results:


Expected results:


Additional info:

Already fixed in upstream:

https://www.redhat.com/archives/lvm-devel/2012-August/msg00062.html

(Before the release of lvm2-2.02.97, there were some changes that've missed to update some related code parts)

verified with lvm2-2.02.98-2.el7.x86_64