- for structure fields that are conditionally present,
make those fields always present.
- for functions which are conditionally inline, make them never inline.
- remove some other functions which are conditionally defined but
don't actually do anything anymore.
- make a lock-debugging function conditional on only LOCKDEBUG.
as discussed on tech-kern some time back.
from Stephan Uphoff, FreeBSD PR/69964.
(http://www.freebsd.org/cgi/query-pr.cgi?pr=69964)
> The LK_WANT_EXCL and LK_WANT_UPGRADE bits act as mini-locks and can block
> other threads.
> Normally this is not a problem since the mini locks are upgraded to full loc
> and the release of the locks will unblock the other threads.
> However if a thread reset the bits without optaining a full lock
> other threads are not awoken.
> This can happens if obtaining the full lock fails because of a LK_SLEEPFAIL,
> or a signal (if lock priority includes PCATCH .. don't think this is used).
ensure that no one else have the same lock.
a patch from Stephan Uphoff, FreeBSD PR/69934.
(http://www.freebsd.org/cgi/query-pr.cgi?pr=69934)
> Upgrading a lock does not play well together with acquiring
> an exclusive lock and can lead to two threads being
> granted exclusive access.
>
> Problematic sequence:
> Thread A acquires a previous unlocked lock in shared mode.
> Thread B tries to acquire the same lock in exclusive mode
> and blocks.
> Thread A upgrades its lock - waking up thread B.
> Thread B wakes up and also acquires the same lock as it only checks
> if the lock is not shared or if someone wants to upgrade the lock
> and not if someone already upgraded the lock to an exclusive lock.
- Not enabled by default. Needs kernel option FFS_SNAPSHOT.
- Change parameters of ffs_blkfree.
- Let the copy-on-write functions return an error so spec_strategy
may fail if the copy-on-write fails.
- Change genfs_*lock*() to use vp->v_vnlock instead of &vp->v_lock.
- Add flag B_METAONLY to VOP_BALLOC to return indirect block buffer.
- Add a function ffs_checkfreefile needed for snapshot creation.
- Add special handling of snapshot files:
Snapshots may not be opened for writing and the attributes are read-only.
Use the mtime as the time this snapshot was taken.
Deny mtime updates for snapshot files.
- Add function transferlockers to transfer any waiting processes from
one lock to another.
- Add vfsop VFS_SNAPSHOT to take a snapshot and make it accessible through
a vnode.
- Add snapshot support to ls, fsck_ffs and dump.
Welcome to 2.0F.
Approved by: Jason R. Thorpe <thorpej@netbsd.org>
