Add error check for id

device_id and cache_id
are checked if they are valid.
Add error check for id

device_id and cache_id
are checked if they are valid.
factor out parse_cache_id.
merge
Add comment on lc_ctr about cache-id param to take
bugfix: lc-detach

Fixed two points
1. nr variable is computed lazily
2. time module is imported

without 2
error emitted in try block is catched by the VM
and context immediately jumps to finally block.
Add and modify comment

Add comment on why we use mutex instead of rw_semaphore
which can run reads concurrently.
Merge branch 'develop' into linux-next