Attilio Rao 83b3bdbc8a Improve VFS locking:
- Implement real draining for vfs consumers by not relying on the
  mnt_lock and using instead a refcount in order to keep track of lock
  requesters.
- Due to the change above, remove the mnt_lock lockmgr because it is now
  useless.
- Due to the change above, vfs_busy() is no more linked to a lockmgr.
  Change so its KPI by removing the interlock argument and defining 2 new
  flags for it: MBF_NOWAIT which basically replaces the LK_NOWAIT of the
  old version (which was unlinked from the lockmgr alredy) and
  MBF_MNTLSTLOCK which provides the ability to drop the mountlist_mtx
  once the mnt interlock is held (ability still desired by most consumers).
- The stub used into vfs_mount_destroy(), that allows to override the
  mnt_ref if running for more than 3 seconds, make it totally useless.
  Remove it as it was thought to work into older versions.
  If a problem of "refcount held never going away" should appear, we will
  need to fix properly instead than trust on such hackish solution.
- Fix a bug where returning (with an error) from dounmount() was still
  leaving the MNTK_MWAIT flag on even if it the waiters were actually
  woken up. Just a place in vfs_mount_destroy() is left because it is
  going to recycle the structure in any case, so it doesn't matter.
- Remove the markercnt refcount as it is useless.

This patch modifies VFS ABI and breaks KPI for vfs_busy() so manpages and
__FreeBSD_version will be modified accordingly.

Discussed with:	kib
Tested by:	pho
2008-11-02 10:15:42 +00:00
2008-10-16 18:09:27 +00:00
2008-08-01 02:48:36 +00:00
2008-11-02 10:15:42 +00:00
2008-10-29 20:19:54 +00:00
2008-10-17 21:14:50 +00:00
2007-12-31 22:09:19 +00:00
2008-06-05 19:47:58 +00:00
2008-06-06 21:32:01 +00:00
2008-07-23 09:33:08 +00:00

This is the top level of the FreeBSD source directory.  This file
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