f2fs: updates on 4.15-rc1

Pull f2fs updates from Jaegeuk Kim:
 "In this round, we introduce sysfile-based quota support which is
  required for Android by default. In addition, we allow that users are
  able to reserve some blocks in runtime to mitigate performance drops
  in low free space.

 Enhancements:
  - assign proper data segments according to write_hints given by user
  - issue cache_flush on dirty devices only among multiple devices
  - exploit cp_error flag and add more faults to enhance fault
    injection test
  - conduct more readaheads during f2fs_readdir
  - add a range for discard commands

Bug fixes:
 - fix zero stat->st_blocks when inline_data is set
 - drop crypto key and free stale memory pointer while evict_inode is
   failing
 - fix some corner cases in free space and segment management
 - fix wrong last_disk_size

This series includes lots of clean-ups and code enhancement in terms
of xattr operations, discard/flush command control. In addition, it
adds versatile debugfs entries to monitor f2fs status"

Cherry-picked from origin/upstream-f2fs-stable-linux-3.18.y:

c6f66cb7 f2fs: deny accessing encryption policy if encryption is off
f3c3ffad f2fs: inject fault in inc_valid_node_count
bc7ed7f3 f2fs: expose quota information in debugfs
c269d143 f2fs: separate nat entry mem alloc from nat_tree_lock
52c43204 f2fs: validate before set/clear free nat bitmap
2007e708 f2fs: avoid opened loop codes in __add_ino_entry
5799a6dd f2fs: apply write hints to select the type of segments for buffered write
d62ae05c f2fs: introduce scan_curseg_cache for cleanup
59b90517 f2fs: optimize the way of traversing free_nid_bitmap
d3754d20 f2fs: keep scanning until enough free nids are acquired
44131bb6 f2fs: trace checkpoint reason in fsync()
e1c850fe f2fs: keep isize once block is reserved cross EOF
9d154a40 f2fs: avoid race in between GC and block exchange
1dd480ac f2fs: save a multiplication for last_nid calculation
5bef5b29 f2fs: fix summary info corruption
a1cc64f1 f2fs: remove dead code in update_meta_page
d86513f6 f2fs: remove unneeded semicolon
24f6fa05 f2fs: don't bother with inode->i_version
c86b0e23 f2fs: check curseg space before foreground GC
4fd29af3 f2fs: use rw_semaphore to protect SIT cache
722458db f2fs: support quota sys files
e5617e7a f2fs: add quota_ino feature infra
468c6095 f2fs: optimize __update_nat_bits
51349d88 f2fs: modify for accurate fggc node io stat
0e42a915 Revert "f2fs: handle dirty segments inside refresh_sit_entry"
71b40527 f2fs: add a function to move nid
8f5dcea4 f2fs: export SSR allocation threshold
1ead0d06 f2fs: give correct trimmed blocks in fstrim
be5d050a f2fs: support bio allocation error injection
710adf1c f2fs: support get_page error injection
a0daae09 f2fs: add missing sysfs description
2606cff9 f2fs: support soft block reservation
30d0b7c1 f2fs: handle error case when adding xattr entry
e254d1a6 f2fs: support flexible inline xattr size
eb25e774 f2fs: show current cp state
bf85becc f2fs: add missing quota_initialize
c3290d76 f2fs: show # of dirty segments via sysfs
02fe062b f2fs: stop all the operations by cp_error flag
d2d06691 f2fs: remove several redundant assignments
04e41a9f f2fs: avoid using timespec
8be4d9e5 f2fs: fix to correct no_fggc_candidate
ec8a71ac Revert "f2fs: return wrong error number on f2fs_quota_write"
c68705b8 f2fs: remove obsolete pointer for truncate_xattr_node
fee61cec f2fs: retry ENOMEM for quota_read|write
585398f7 f2fs: limit # of inmemory pages
e0ac8d0a f2fs: update ctx->pos correctly when hitting hole in directory
f6e29ede f2fs: relocate readahead codes in readdir()
d88ba788 f2fs: allow readdir() to be interrupted
710c0b07 f2fs: trace f2fs_readdir
6ff204b6 f2fs: trace f2fs_lookup
0c33cb26 f2fs: skip searching non-exist range in truncate_hole
1aead705 f2fs: expose some sectors to user in inline data or dentry case
b9da516c f2fs: avoid stale fi->gdirty_list pointer
68a76f16 f2fs/crypto: drop crypto key at evict_inode only
93bb7f1d f2fs: fix to avoid race when accessing last_disk_size
cc71a4a9 f2fs: Fix bool initialization/comparison
549f9f84 f2fs: give up CP_TRIMMED_FLAG if it drops discards
87905eb8 f2fs: trace f2fs_remove_discard
b791197f f2fs: reduce cmd_lock coverage in __issue_discard_cmd
d156194c f2fs: split discard policy
4b92a1f4 f2fs: wrap discard policy
0f5a1368 f2fs: support issuing/waiting discard in range
9c9d6ab9 f2fs: fix to flush multiple device in checkpoint
98e85b90 f2fs: enhance multiple device flush
97acaf71 f2fs: fix to show ino management cache size correctly
9e089394 f2fs: drop FI_UPDATE_WRITE tag after f2fs_issue_flush
b5b73718 f2fs: obsolete ALLOC_NID_LIST list
33646c98 f2fs: convert inline data for direct I/O & FI_NO_PREALLOC
8e68de1c f2fs: allow readpages with NULL file pointer
5c1821a8 f2fs: show flush list status in sysfs
ca433f07 f2fs: introduce read_xattr_block
e002c811 f2fs: introduce read_inline_xattr
9944032a Revert "f2fs: reuse nids more aggressively"
bc58a366 Revert "f2fs: node segment is prior to data segment selected victim"

Change-Id: I67cdc08f7bfca2da8b434fec66a779705c0ed5b2
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>