xen/dev: remove __unused from driver argument of identify functions

The driver argument is most certainly now used by these functions. When
originally implemented it might have been unused, but not now.

Reviewed by: royger

sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

xen: Remove unused devclass arguments to DRIVER_MODULE.

xen: allow limiting the amount of duplicated pending xenstore watches

Xenstore watches received are queued in a list and processed in a
deferred thread. Such queuing was done without any checking, so a
guest could potentially trigger a resource starvation against the
FreeBSD kernel if such kernel is watching any user-controlled xenstore
path.

Allowing limiting the amount of pending events a watch can accumulate
to prevent a remote guest from triggering this resource starvation
issue.

For the PV device backends and frontends this limitation is only
applied to the other end /state node, which is limited to 1 pending
event, the rest of the watched paths can still have unlimited pending
watches because they are either local or controlled by a privileged
domain.

The xenstore user-space device gets special treatment as it's not
possible for the kernel to know whether the paths being watched by
user-space processes are controlled by a guest domain. For this reason
watches set by the xenstore user-space device are limited to 1000
pending events. Note this can be modified using the
max_pending_watch_events sysctl of the device.

This is XSA-349.

Sponsored by: Citrix Systems R&D
MFC after: 3 days

dev/xen: clean up empty lines in .c and .h files

dev/xenstore: prevent transaction hijacking

The user-space xenstore device is currently lacking a check to make
sure that the caller is only using transaction ids currently assigned
to it. This allows users of the xenstore device to hijack transactions
not started by them, although the scope is limited to transactions
started by the same domain.

Tested by: Nathan Friess <nathan.friess@gmail.com>
Sponsored by: Citrix Systems R&D

dev/xenstore: add support for watches

Allow user-space applications to register watches using the xenstore
device. This is needed in order to run toolstack operations on
domains different than the one where xenstore is running (in which
case the device is not used, since the connection to xenstore is done
using a plain socket).

Tested by: Nathan Friess <nathan.friess@gmail.com>
Sponsored by: Citrix Systems R&D

sys/dev: minor spelling fixes.

Most affect comments, very few have user-visible effects.

xen: fix xenstore dev

Xenstore user-space device has two problems currently:
- It does not correctly handle concurrent clients, because it's storing
each client data in dev->si_drv1.
- It does not correctly free this data when the client closes the device.

In order to solve both of this issues store the per-client data using
cdevpriv, which also comes with a hook in order to perform the necessary
cleanup on device close.

While there also make the device eternal.

Sponsored by: Citrix Systems R&D
Reported and Tested by: thompsa
MFC after: 2 weeks

xen: convert the xenstore user-space char device to a newbus device

Convert the xenstore user-space device (/dev/xen/xenstore) to a device
using the newbus interface. This allows us to make the device
initialization dependant on the initialization of xenstore itself in
the kernel.

Sponsored by: Citrix Systems R&D

dev/xen/xenstore/xenstore.c:
- Convert to a newbus device, this removes the xs_dev_init function.

xen/xenstore/xenstore_internal.h:
- Remove xs_dev_init prototype.

dev/xen/xenstore/xenstore.c:
- Don't call xs_dev_init anymore, the device will attach itself when
xenstore is started.

xen: move xenstore devices

Move xenstore related devices (xenstore.c and xenstore_dev.c) from
xen/xenstore to dev/xen/xenstore. This is just code motion, no
functional changes.

Sponsored by: Citrix Systems R&D