[PATCH v6 00/15] Create and use APIs to centralise locking for directory ops.

[NeilBrown]

Following is a new version of this series:
 - fixed a bug found by syzbot
 - cleanup suggested by Stephen Smalley
 - added patch for missing updates in smb/server - thanks Jeff Layton
 - various s-o-b


Previous description:

 this series is the next part of my effort to change directory-op
 locking to allow multiple concurrent ops in a directory.  Ultimately we
 will (in my plan) lock the target dentry(s) rather than the whole
 parent directory.

 To help with changing the locking protocol, this series centralises
 locking and lookup in some helpers.  The various helpers are introduced
 and then used in the same patch - roughly one patch per helper though
 with various exceptions.

 I haven't introduced these helpers into the various filesystems that
 Al's tree-in-dcache series is changing.  That series introduces and
 uses similar helpers tuned to the specific needs of that set of
 filesystems.  Ultimately all the helpers will use the same backends
 which can then be adjusted when it is time to change the locking
 protocol.

 One change that deserves highlighting is in patch 13 where vfs_mkdir()
 is changed to unlock the parent on failure, as well as the current
 behaviour of dput()ing the dentry on failure.  Once this change is in
 place, the final step of both create and an remove sequences only
 requires the target dentry, not the parent.  So e.g.  end_creating() is
 only given the dentry (which may be IS_ERR() after vfs_mkdir()).  This
 helps establish the pattern that it is the dentry that is being locked
 and unlocked (the lock is currently held on dentry->d_parent->d_inode,
 but that can change).

 Please review the changes I've made to your respective code areas and
 let us know of any problems.

Thanks,
NeilBrown


 [PATCH v6 01/15] debugfs: rename end_creating() to
 [PATCH v6 02/15] VFS: introduce start_dirop() and end_dirop()
 [PATCH v6 03/15] VFS: tidy up do_unlinkat()
 [PATCH v6 04/15] VFS/nfsd/cachefiles/ovl: add start_creating() and
 [PATCH v6 05/15] VFS/nfsd/cachefiles/ovl: introduce start_removing()
 [PATCH v6 06/15] VFS: introduce start_creating_noperm() and
 [PATCH v6 07/15] smb/server: use end_removing_noperm for for target
 [PATCH v6 08/15] VFS: introduce start_removing_dentry()
 [PATCH v6 09/15] VFS: add start_creating_killable() and
 [PATCH v6 10/15] VFS/nfsd/ovl: introduce start_renaming() and
 [PATCH v6 11/15] VFS/ovl/smb: introduce start_renaming_dentry()
 [PATCH v6 12/15] Add start_renaming_two_dentries()
 [PATCH v6 13/15] ecryptfs: use new start_creating/start_removing APIs
 [PATCH v6 14/15] VFS: change vfs_mkdir() to unlock on failure.
 [PATCH v6 15/15] VFS: introduce end_creating_keep()