- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Rework the underlying ALQ storage to be a circular buffer, which amongst other
things allows variable length messages to be easily supported.

- Extend KPI with alq_writen() and alq_getn() to support variable length
messages, which is enabled at ALQ creation time depending on the
arguments passed to alq_open(). Also add variants of alq_open() and
alq_post() that accept a flags argument. The KPI is still fully
backwards compatible and shouldn't require any change in ALQ consumers
unless they wish to utilise the new features.

- Introduce the ALQ_NOACTIVATE and ALQ_ORDERED flags to allow ALQ consumers
to have more control over IO scheduling and resource acquisition
respectively.

- Strengthen invariants checking.

- Document ALQ changes in ALQ(9) man page.

Sponsored by: FreeBSD Foundation
Reviewed by: gnn, jeff, rpaulo, rwatson
MFC after: 1 month

Modify the alq(9) alq_open() API to accept a file creation mode, rather
than defaulting the cmode argument to vn_open() to 0. Supply a default
argument of ALQ_DEFAULT_CMODE (0600) in current callers.

Discussed with/pointed out by: hmp
Reveiwed by: jeff, hmp
MFC after: 3 days

/* -> /*- for license, minor formatting changes

Add an explicit credential argument to alq_open() to allow the caller to
specify what credential to use when authorizing vn_open() and later
write operations, rather than curthread->td_ucred.

When writing KTR traces to an ALQ, specify the credential of the thread
generating the sysctl request.

Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories

- Export the alq daemon thread pointer.
- Don't log ktr events from the alq daemon.

- Correct the name in the header guards.

Spotted by: rwatson

- Add an asynchronous fixed length record logging mechanism called
ALQ (Asynch. Logging Queues). ALQ supports many seperate queues with
different record and buffer sizes. It opens and logs to any vnode so
it can be used with character devices as well as regular files.

Reviewed in part by: phk, jake, markm