Several enhancements to the Xen block back driver.

sys/dev/xen/blkback/blkback.c:
	o Implement front-end request coalescing.  This greatly improves the
	  performance of front-end clients that are unaware of the dynamic
	  request-size/number of requests negotiation available in the
	  FreeBSD backend driver.  This required a large restructuring
	  in how this driver records in-flight transactions and how those
	  transactions are mapped into kernel KVA.  For example, the driver
	  now includes a mini "KVA manager" that allocates ranges of
	  contiguous KVA to patches of requests that are physically
	  contiguous in the backing store so that a single bio or UIO
	  segment can be used to represent the I/O.

	o Refuse to open any backend files or devices if the system
	  has yet to mount root.  This avoids a panic.

	o Properly handle "onlined" devices.  An "onlined" backend
	  device stays attached to its backing store across front-end
	  disconnections.  This feature is intended to reduce latency
	  when a front-end does a hand-off to another driver (e.g.
	  PV aware bootloader to OS kernel) or during a VM reboot.

	o Harden the driver against a pathological/buggy front-end
	  by carefully vetting front-end XenStore data such as the
	  front-end state.

	o Add sysctls that report the negotiated number of
	  segments per-request and the number of requests that
	  can be concurrently in flight.

Submitted by:	kdm
Reviewed by:	gibbs
Sponsored by:	Spectra Logic Corporation
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions