[dm-devel] Snapshot origin table as P/PO snapshot with /dev/null

[Navin P.S]

Hi,
  If i have a snapshot origin created using dmsetup create table with a
mapping  real device  with (major,minor) =(8,18) and lets name it
/dev/mapper/dmso . Now the set of reads are writes done from
/dev/mapper/dmso have some values (R,W).

Had i been creating a persistent snapshot using (P or PO) mode with origin
device as /dev/null and COW device is my real device (maj,min)=8,18 and it
is named as /dev/mapper/dmsp. Now if i do the exact same reads and writes
that i did to dmso (snapshot-origin) , will get i the same set of output
values (R,W).

In my experiment i did. So i'm asking is there a case where it differs ?

Also i looked at the code in drivers/md/dm-snap.c and i find that both the
drivers snapshot and snapshot-origin use the same __orgin_write . So my
partial/incomplete understanding is that it works from the read/write view
point from /dev/mapper/dmsp.

I'll not be using the snapshot-merge feature , so merging to /dev/null is
irrelevant here.

Regards,
-- Navin
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