ceph/src/TODO

v0.5
/- debug restart, cosd reformat, etc.
/- finish btrfs ioctl interface
/- efficient snap recovery
/- throttle osd recovery
/- forced unmount?

v0.6
- ENOSPC
- async metadata ops

v0.7
- cas?

big items
- finish client failure recovery (reconnect after long eviction; and slow delayed reconnect)
- ENOSPC
  - space reservation in ObjectStore, redeemed by Transactions?
  - reserved as PG goes active; reservation canceled when pg goes inactive
  - something similar during recovery
  - ?
- repair
- enforceable quotas?
- mds security enforcement
- client, user authentication
- cas
- osd failure declarations
- libuuid?


repair
- are we concerned about
  - scrubbing
  - reconstruction after loss of subset of cdirs
  - reconstruction after loss of md log
- data object 
  - path backpointers?
  - parent dir pointer?
- cdir objects
  - parent dir pointer
    - update on rename?  or on cdir store?
      on cdir store is sufficient if mdlog survives...
  - or what the hell, full trace?
- mds scrubbing
- rados scrubbing

snaps on osd
- garbage collection
  - don't start collection on replica until clean?
- efficient recovery of clones using the clone diff info
  - recovery on primary
    - log order vs recovery/clone order?
    - rep_op_push on primary needs to be smart
    - IndexLog could somehow aggregate data_subsets?
  - primary pushes to replicas
    - clone/rename, + push of new head


kernel client
- make osd retry writes if failure after ack..
- ACLs
- reconnect path should include pathbase, not just a string?
- make writepages maybe skip pages with errors?
  - EIO, or ENOSPC?
  - ... writeback vs ENOSPC vs flush vs close()... hrm...
- set mapping bits for ENOSPC, EIO?
- flush caps on sync, fsync, etc.
  - do we need to block?  how do we track that?
- forced unmount?
- procfs/debugfs
  - adjust granular debug levels too
    - should we be using debugfs?
  - a dir for each client instance (client###)?
  - hooks to get mds, osd, monmap epoch #s
- populate sysfs?
  - things that would be useful to see
    - fsid
    - map versions on client
    - outstanding mds, osd, mon requests?
- fix readdir vs fragment race by keeping a separate frag pos, and ignoring dentries below it
- reconnect after being disconnected from the mds

kclient items to review
- fill_trace locking
- async trunc
- async writeback
- cache invalidation race, locking problems
  - cap changes are serialized by i_lock, but (thorough) cache invalidation may block..


vfs issues
- real_lookup() race:
  1- hash lookup find no dentry
  2- real_lookup() takes dir i_mutex, but then finds a dentry
  3- drops mutex, then calld d_revalidate.  if that fails, we return ENOENT (instead of looping?)
- vfs_rename_dir()

userspace client
- handle session STALE
- time out caps, wake up waiters on renewal
  - link caps with mds session
- validate dn leases
- fix lease validation to check session ttl
- clean up ll_ interface, now that we have leases!
- clean up client mds session vs mdsmap behavior?
- stop using mds's inode_t?
- fix readdir vs fragment race by keeping a separate frag pos, and ignoring dentries below it

mds
- hard link backpointers
  - anchor source dir
  - build snaprealm for any hardlinked file
  - include snaps for all (primary+remote) parents

- how do we properly clean up inodes when doing a snap purge?
  - when they are mid-recover?  see 136470cf7ca876febf68a2b0610fa3bb77ad3532

- whats with the 'clear if dirtyscattered' bit in decode_import_inode()?

- what if a recovery is queued, or in progress, and the inode is then cowed?  can that happen?  

- proper handling of cache expire messages during rejoin phase?
  -> i think cache expires are fine; the rejoin_ack handler just has to behave if rejoining items go missing
- try_remove_unlinked_dn thing

- rename: importing inode... also journal imported client map?

- rerun destro trace against latest, with various journal lengths

- lease length heuristics
  - mds lock last_change stamp?

- handle slow client reconnect (i.e. after mds has gone active)

- fix reconnect/rejoin open file weirdness

- can we get rid of the dirlock remote auth_pin weirdness on subtree roots?
- anchor_destroy needs to xlock linklock.. which means it needs a Mutation wrapper?
  - ... when it gets a caller.. someday..

- make truncate faster with a trunc_seq, attached to objects as attributes?

- osd needs a set_floor_and_read op for safe failover/STOGITH-like semantics.

- could mark dir complete in EMetaBlob by counting how many dentries are dirtied in the current log epoch in CDir...

- FIXME how to journal/store root and stray inode content? 
  - in particular, i care about dirfragtree.. get it on rejoin?
  - and dir sizes, if i add that... also on rejoin?

- efficient stat for single writers
- add FILE_CAP_EXTEND capability bit


journaler
- fix up for large events (e.g. imports)
- use set_floor_and_read for safe takeover from possibly-not-quite-dead otherguy.
- should we pad with zeros to avoid splitting individual entries?
  - make it a g_conf flag?
  - have to fix reader to skip over zeros (either <4 bytes for size, or zeroed sizes)
- need to truncate at detected (valid) write_pos to clear out any other partial trailing writes


osdmon
- monitor needs to monitor some osds...

crush
- allow forcefeed for more complicated rule structures.  (e.g. make force_stack a list< set<int> >)
- "knob" bucket

pgmon
- include osd vector with pg state
  - check for orphan pgs
- monitor pg states, notify on out?
- watch osd utilization; adjust overload in cluster map

mon
- paxos need to clean up old states.
- some sort of tester for PaxosService...
- osdmon needs to lower-bound old osdmap versions it keeps around?

objecter
- fix failure handler...
  - generic mon client?
- maybe_request_map should set a timer event to periodically re-request.
- transaction prepare/commit?
- read+floor_lockout

osd
- snap_trimmers should detect, remove unused snap collections (and update snap_collections set)
- cope with divergent logs (update AND removal) in merge_log...
  (make merge_log augment omissing?)

- how does an admin intervene when a pg needs a dead osd to repeer?

- a more general fencing mechanism?  per-object granularity isn't usually a good match.

- consider implications of nvram writeahead logs

- flag missing log entries on crash recovery  --> WRNOOP? or WRLOST?

- efficiently replicate clone() objects
- fix heartbeat wrt new replication
- mark residual pgs obsolete  ???
- rdlocks
- optimize remove wrt recovery pushes

simplemessenger
- close idle connections

objectcacher
- merge clean bh's
- ocacher caps transitions vs locks
- test read locks

ebofs
- btrees
  - checksums
  - dups
  - sets

- optionally scrub deallocated extents
- clone()

- map ObjectStore

- verify proper behavior of conflicting/overlapping reads of clones
- combine inodes and/or cnodes into same blocks
- fix bug in node rotation on insert (and reenable)
- fix NEAR_LAST_FWD (?)

- awareness of underlying software/hardware raid in allocator so that we
  write full stripes _only_.
  - hmm, that's basically just a large block size.

- rewrite the btree code!
  - multithreaded
  - eliminate nodepools
  - allow btree sets
  - allow arbitrary embedded data?
  - allow arbitrary btrees
  - allow root node(s?) to be embedded in onode, or whereever.
  - keys and values can be uniform (fixed-size) or non-uniform.  
    - fixed size (if any) is a value in the btree struct.  
      - negative indicates bytes of length value?  (1 -> 255bytes, 2 -> 65535 bytes, etc.?)
    - non-uniform records preceeded by length.  
    - keys sorted via a comparator defined in btree root.  
      - lexicographically, by default.

- goal
  - object btree key->value payload, not just a data blob payload.
  - better threading behavior.
    - with transactional goodness!

- onode
  - object attributes.. as a btree?
  - blob stream
  - map stream.
    - allow blob values.


remaining hard problems
- how to cope with file size changes and read/write sharing