Pull second SCSI update from James "Jaj B" Bottomley:
 "This is the final round of SCSI patches for the merge window.  It
  consists mostly of driver updates (bnx2fc, ibmfc, fnic, lpfc,
  be2iscsi, pm80xx, qla4x and ipr).

  There's also the power management updates that complete the patches in
  Jens' tree, an iscsi refcounting problem fix from the last pull, some
  dif handling in scsi_debug fixes, a few nice code cleanups and an
  error handling busy bug fix."

* tag 'scsi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi: (92 commits)
  [SCSI] qla2xxx: Update firmware link in Kconfig file.
  [SCSI] iscsi class, qla4xxx: fix sess/conn refcounting when find fns are used
  [SCSI] sas: unify the pointlessly separated enums sas_dev_type and sas_device_type
  [SCSI] pm80xx: thermal, sas controller config and error handling update
  [SCSI] pm80xx: NCQ error handling changes
  [SCSI] pm80xx: WWN Modification for PM8081/88/89 controllers
  [SCSI] pm80xx: Changed module name and debug messages update
  [SCSI] pm80xx: Firmware flash memory free fix, with addition of new memory region for it
  [SCSI] pm80xx: SPC new firmware changes for device id 0x8081 alone
  [SCSI] pm80xx: Added SPCv/ve specific hardware functionalities and relevant changes in common files
  [SCSI] pm80xx: MSI-X implementation for using 64 interrupts
  [SCSI] pm80xx: Updated common functions common for SPC and SPCv/ve
  [SCSI] pm80xx: Multiple inbound/outbound queue configuration
  [SCSI] pm80xx: Added SPCv/ve specific ids, variables and modify for SPC
  [SCSI] lpfc: fix up Kconfig dependencies
  [SCSI] Handle MLQUEUE busy response in scsi_send_eh_cmnd
  [SCSI] sd: change to auto suspend mode
  [SCSI] sd: use REQ_PM in sd's runtime suspend operation
  [SCSI] qla4xxx: Fix iocb_cnt calculation in qla4xxx_send_mbox_iocb()
  [SCSI] ufs: Correct the expected data transfersize
  ...

Pull idle update from Len Brown:
 "Add support for new Haswell-ULT CPU idle power states"

* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux:
  intel_idle: initial C8, C9, C10 support
  tools/power turbostat: display C8, C9, C10 residency

Pull audit changes from Eric Paris:
 "Al used to send pull requests every couple of years but he told me to
  just start pushing them to you directly.

  Our touching outside of core audit code is pretty straight forward.  A
  couple of interface changes which hit net/.  A simple argument bug
  calling audit functions in namei.c and the removal of some assembly
  branch prediction code on ppc"

* git://git.infradead.org/users/eparis/audit: (31 commits)
  audit: fix message spacing printing auid
  Revert "audit: move kaudit thread start from auditd registration to kaudit init"
  audit: vfs: fix audit_inode call in O_CREAT case of do_last
  audit: Make testing for a valid loginuid explicit.
  audit: fix event coverage of AUDIT_ANOM_LINK
  audit: use spin_lock in audit_receive_msg to process tty logging
  audit: do not needlessly take a lock in tty_audit_exit
  audit: do not needlessly take a spinlock in copy_signal
  audit: add an option to control logging of passwords with pam_tty_audit
  audit: use spin_lock_irqsave/restore in audit tty code
  helper for some session id stuff
  audit: use a consistent audit helper to log lsm information
  audit: push loginuid and sessionid processing down
  audit: stop pushing loginid, uid, sessionid as arguments
  audit: remove the old depricated kernel interface
  audit: make validity checking generic
  audit: allow checking the type of audit message in the user filter
  audit: fix build break when AUDIT_DEBUG == 2
  audit: remove duplicate export of audit_enabled
  Audit: do not print error when LSMs disabled
  ...

Pull nfsd fixes from Bruce Fields:
 "Small fixes for two bugs and two warnings"

* 'for-3.10' of git://linux-nfs.org/~bfields/linux:
  nfsd: fix oops when legacy_recdir_name_error is passed a -ENOENT error
  SUNRPC: fix decoding of optional gss-proxy xdr fields
  SUNRPC: Refactor gssx_dec_option_array() to kill uninitialized warning
  nfsd4: don't allow owner override on 4.1 CLAIM_FH opens

Pull x86 platform drivers from Matthew Garrett:
 "Small set of updates, mainly trivial bugfixes and some small updates
  to deal with newer hardware.

  There's also a new driver that allows qemu guests to notify the
  hypervisor that they've just paniced, which seems useful."

* 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86:
  Add support for fan button on Ideapad Z580
  pvpanic: pvpanic device driver
  asus-nb-wmi: set wapf=4 for ASUSTeK COMPUTER INC. X75A
  drivers: platform: x86: Use PTR_RET function
  sony-laptop: SVS151290S kbd backlight and gfx switch support
  hp-wmi: add more definitions for new event_id's
  dell-laptop: Fix krealloc() misuse in parse_da_table()
  hp_accel: Ignore the error from lis3lv02d_poweron() at resume
  dell: add new dell WMI format for the AIO machines

Pull stray syscall bits from Al Viro:
 "Several syscall-related commits that were missing from the original"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal:
  switch compat_sys_sysctl to COMPAT_SYSCALL_DEFINE
  unicore32: just use mmap_pgoff()...
  unify compat fanotify_mark(2), switch to COMPAT_SYSCALL_DEFINE
  x86, vm86: fix VM86 syscalls: use SYSCALL_DEFINEx(...)

Merge tag 'ecryptfs-3.10-rc1-ablkcipher' of git://git.kernel.org/pub/scm/linux/kernel/git/tyhicks/ecryptfs

Pull eCryptfs update from Tyler Hicks:
 "Improve performance when AES-NI (and most likely other crypto
  accelerators) is available by moving to the ablkcipher crypto API.
  The improvement is more apparent on faster storage devices.

  There's no noticeable change when hardware crypto is not available"

* tag 'ecryptfs-3.10-rc1-ablkcipher' of git://git.kernel.org/pub/scm/linux/kernel/git/tyhicks/ecryptfs:
  eCryptfs: Use the ablkcipher crypto API

Pull misc fixes from David Woodhouse:
 "This is some miscellaneous cleanups that don't really belong anywhere
  else (or were ignored), that have been sitting in linux-next for some
  time.  Two of them are fixes resulting from my audit of krealloc()
  usage that don't seem to have elicited any response when I posted
  them, and the other three are patches from Artem removing dead code."

* tag 'for-linus-20130509' of git://git.infradead.org/~dwmw2/random-2.6:
  pcmcia: remove RPX board stuff
  m68k: remove rpxlite stuff
  pcmcia: remove Motorola MBX860 support
  params: Fix potential memory leak in add_sysfs_param()
  dell-laptop: Fix krealloc() misuse in parse_da_table()

Pull kvm fixes from Gleb Natapov:
 "Most of the fixes are in the emulator since now we emulate more than
  we did before for correctness sake we see more bugs there, but there
  is also an OOPS fixed and corruption of xcr0 register."

* tag 'kvm-3.10-2' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: emulator: emulate SALC
  KVM: emulator: emulate XLAT
  KVM: emulator: emulate AAM
  KVM: VMX: fix halt emulation while emulating invalid guest sate
  KVM: Fix kvm_irqfd_init initialization
  KVM: x86: fix maintenance of guest/host xcr0 state

Pull device-mapper updates from Alasdair Kergon:
 "Allow devices that hold metadata for the device-mapper thin
  provisioning target to be extended easily; allow WRITE SAME on
  multipath devices; an assortment of little fixes and clean-ups."

* tag 'dm-3.10-changes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm: (21 commits)
  dm cache: set config value
  dm cache: move config fns
  dm thin: generate event when metadata threshold passed
  dm persistent metadata: add space map threshold callback
  dm persistent data: add threshold callback to space map
  dm thin: detect metadata device resizing
  dm persistent data: support space map resizing
  dm thin: open dev read only when possible
  dm thin: refactor data dev resize
  dm cache: replace memcpy with struct assignment
  dm cache: fix typos in comments
  dm cache policy: fix description of lookup fn
  dm: document iterate_devices
  dm persistent data: fix error message typos
  dm cache: tune migration throttling
  dm mpath: enable WRITE SAME support
  dm table: fix write same support
  dm bufio: avoid a possible __vmalloc deadlock
  dm snapshot: fix error return code in snapshot_ctr
  dm cache: fix error return code in cache_create
  ...

Pull HID fixes from Jiri Kosina:

 - fix usage of sleeping lock in atomic context from Jiri Kosina

 - build fix for hid-steelseries under certain .config setups by Simon Wood

 - simple mismerge fix from Fernando Luis Vázquez Cao

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid:
  HID: debug: fix RCU preemption issue
  HID: hid-steelseries fix led class build issue
  HID: reintroduce fix-up for certain Sony RF receivers

Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Pull sound fixes from Takashi Iwai:
 "This contains small fixes since the previous pull request:

   - A few regression fixes and small updates of HD-audio

   - Yet another fix for Haswell HDMI audio

   - A copule of trivial fixes in ASoC McASP, DPAM and WM8994"

* tag 'sound-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound:
  Revert "ALSA: hda - Don't set up active streams twice"
  ALSA: Add comment for control TLV API
  ALSA: hda - Apply pin-enablement workaround to all Haswell HDMI codecs
  ALSA: HDA: Fix Oops caused by dereference NULL pointer
  ALSA: mips/sgio2audio: Remove redundant platform_set_drvdata()
  ALSA: mips/hal2: Remove redundant platform_set_drvdata()
  ALSA: hda - Fix 3.9 regression of EAPD init on Conexant codecs
  sound: Fix make allmodconfig on MIPS
  ALSA: hda - Fix system panic when DMA > 40 bits for Nvidia audio controllers
  ALSA: atmel: Remove redundant platform_set_drvdata()
  ASoC: McASP: Fix receive clock polarity in DAIFMT_NB_NF mode.
  ASoC: wm8994: missing break in wm8994_aif3_hw_params()
  ASoC: McASP: Add pins output direction for rx clocks when configured in CBS_CFS format
  ASoC: dapm: use clk_prepare_enable and clk_disable_unprepare

Pull MIPS updates from Ralf Baechle:

 - More work on DT support for various platforms

 - Various fixes that were to late to make it straight into 3.9

 - Improved platform support, in particular the Netlogic XLR and
   BCM63xx, and the SEAD3 and Malta eval boards.

 - Support for several Ralink SOC families.

 - Complete support for the microMIPS ASE which basically reencodes the
   existing MIPS32/MIPS64 ISA to use non-constant size instructions.

 - Some fallout from LTO work which remove old cruft and will generally
   make the MIPS kernel easier to maintain and resistant to compiler
   optimization, even in absence of LTO.

 - KVM support.  While MIPS has announced hardware virtualization
   extensions this KVM extension uses trap and emulate mode for
   virtualization of MIPS32.  More KVM work to add support for VZ
   hardware virtualizaiton extensions and MIPS64 will probably already
   be merged for 3.11.

Most of this has been sitting in -next for a long time.  All defconfigs
have been build or run time tested except three for which fixes are being
sent by other maintainers.

Semantic conflict with kvm updates done as per Ralf

* 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus: (118 commits)
  MIPS: Add new GIC clockevent driver.
  MIPS: Formatting clean-ups for clocksources.
  MIPS: Refactor GIC clocksource code.
  MIPS: Move 'gic_frequency' to common location.
  MIPS: Move 'gic_present' to common location.
  MIPS: MIPS16e: Add unaligned access support.
  MIPS: MIPS16e: Support handling of delay slots.
  MIPS: MIPS16e: Add instruction formats.
  MIPS: microMIPS: Optimise 'strnlen' core library function.
  MIPS: microMIPS: Optimise 'strlen' core library function.
  MIPS: microMIPS: Optimise 'strncpy' core library function.
  MIPS: microMIPS: Optimise 'memset' core library function.
  MIPS: microMIPS: Add configuration option for microMIPS kernel.
  MIPS: microMIPS: Disable LL/SC and fix linker bug.
  MIPS: microMIPS: Add vdso support.
  MIPS: microMIPS: Add unaligned access support.
  MIPS: microMIPS: Support handling of delay slots.
  MIPS: microMIPS: Add support for exception handling.
  MIPS: microMIPS: Floating point support.
  MIPS: microMIPS: Fix macro naming in micro-assembler.
  ...

Signed-off-by: Giridhar Malavali <giridhar.malavali@qlogic.com>
Signed-off-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

This fixes a bug where the iscsi class/driver did not do a put_device
when a sess/conn device was found. This also simplifies the interface
by not having to pass in some arguments that were duplicated and did
not need to be exported.

Reported-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

These enums have been separate since the dawn of SAS, mainly because the
latter is a procotol only enum and the former includes additional state
for libsas.  The dichotomy causes endless confusion about which one you
should use where and leads to pointless warnings like this:

drivers/scsi/mvsas/mv_sas.c: In function 'mvs_update_phyinfo':
drivers/scsi/mvsas/mv_sas.c:1162:34: warning: comparison between 'enum sas_device_type' and 'enum sas_dev_type' [-Wenum-compare]

Fix by eliminating one of them.  The one kept is effectively the sas.h
one, but call it sas_device_type and make sure the enums are all
properly namespaced with the SAS_ prefix.

Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Modified thermal configuration to happen after interrupt registration
Added SAS controller configuration during initialization
Added error handling logic to handle I_T_Nexus errors and variants

[jejb: fix up tabs and spaces issues]
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Handled NCQ errors in the low level driver as the FW
is not providing the faulty tag for NCQ errors for libsas
to recover.

[jejb: fix checkpatch issues]
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Individual WWN read operations based on controller.
PM8081 - Read WWN from Flash VPD.
PM8088/89 - Read WWN from EEPROM.
PM8001 - Read WWN from NVM.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Changed name in driver to pm80xx. Updated debug messages.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Performing pci_free_consistent in tasklet had result in a core dump. So
allocated a new memory region for it. Fix for passing proper address
and operation in firmware flash update.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Additional bar shift for new SPC firmware, applicable to device
id 0x8081 only.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Implementation of SPCv/ve specific hardware functionality and
macros. Changing common functionalities wrt SPCv/ve operations.
Conditional checks for SPC specific operations.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Implementation of interrupt handlers and tasklets to support
upto 64 interrupt for the device.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Update of function prototype for common function to SPC and SPCv/ve.
Multiple queues implementation for IO.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Memory allocation and configuration of multiple inbound and
outbound queues.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Updated pci id table with device, vendor, subdevice and subvendor ids
for 8081, 8088, 8089 SAS/SATA controllers. Added SPCv/ve related macros.
Updated macros, hba info structure and other structures for SPCv/ve.
Update of structure and variable names for SPC hardware functionalities.

Signed-off-by: Sakthivel K <Sakthivel.SaravananKamalRaju@pmcs.com>
Signed-off-by: Anand Kumar S <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

lpfc uses the generic checksum as well as the T10DIF one from the lib/
directory, so make sure they're selected.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

scsi_send_eh_cmnd() is calling queuecommand() directly, so
it needs to check the return value here.
The only valid return codes for queuecommand() are 'busy'
states, so we need to wait for a bit to allow the LLDD
to recover.

Based on an earlier patch from Wen Xiong.

[jejb: fix confusion between msec and jiffies values and other issues]
[bvanassche: correct stall_for interval]
Cc: Wen Xiong <wenxiong@linux.vnet.ibm.com>
Cc: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Pull second set of arc arch updates from Vineet Gupta:
 "Aliasing VIPT dcache support for ARC

  I'm satisified with testing, specially with fuse which has
  historically given grief to VIPT arches (ARM/PARISC...)"

* tag 'arc-v3.10-rc1-part2' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc:
  ARC: [TB10x] Remove GENERIC_GPIO
  ARC: [mm] Aliasing VIPT dcache support 4/4
  ARC: [mm] Aliasing VIPT dcache support 3/4
  ARC: [mm] Aliasing VIPT dcache support 2/4
  ARC: [mm] Aliasing VIPT dcache support 1/4
  ARC: [mm] refactor the core (i|d)cache line ops loops
  ARC: [mm] serious bug in vaddr based icache flush

Pull m68knommu updates from Greg Ungerer:
 "The bulk of the changes are generalizing the ColdFire v3 core support
  and adding in 537x CPU support.  Also a couple of other bug fixes, one
  to fix a reintroduction of a past bug in the romfs filesystem nommu
  support."

* 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu:
  m68knommu: enable Timer on coldfire 532x
  m68knommu: fix ColdFire 5373/5329 QSPI base address
  m68knommu: add support for configuring a Freescale M5373EVB board
  m68knommu: add support for the ColdFire 537x family of CPUs
  m68knommu: make ColdFire M532x platform support more v3 generic
  m68knommu: create and use a common M53xx ColdFire class of CPUs
  m68k: remove unused asm/dbg.h
  m68k: Set ColdFire ACR1 cache mode depending on kernel configuration
  romfs: fix nommu map length to keep inside filesystem
  m68k: clean up unused "config ROMVECSIZE"

Pull blackfin updates from Steven Miao.

* tag 'for-linus' of git://github.com/realmz/blackfin-linux:
  bfin cache: dcplb map: add 16M dcplb map for BF60x
  blackfin: smp: fix smp build after drop asm/system.h
  blackfin: fix bootup core clock and system clock display
  Platform Nand: Set the GPIO for NAND read as input
  blackfin: rename vmImage to uImage after we move to buildroot
  blackfin: twi: Remove bogus #endif
  bf609: rsi: Add bf609 rsi MMR macro and board platform data.
  blackfin: dmc: Improve DDR2 write through in DMC effict controller.

Pull microblaze updates from Michal Simek.

* 'next' of git://git.monstr.eu/linux-2.6-microblaze:
  microblaze: Enable IRQ in arch_cpu_idle
  microblaze: Fix uaccess_ok macro
  microblaze: Add support for new cpu versions and target architecture
  microblaze: Do not select OPT_LIB_ASM by default
  microblaze: Fix initrd support
  microblaze: Do not use r6 in head.S
  microblaze: pci: Remove duplicated header
  microblaze: Set the default irq_domain
  microblaze: pci: Remove duplicated include from pci-common.c

Share configuration option processing code between the dm cache
ctr and message functions.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Move process_config_option() in dm-cache-target.c to make the
next patch more readable.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Generate a dm event when the amount of remaining thin pool metadata
space falls below a certain level.

The threshold is taken to be a quarter of the size of the metadata
device with a minimum threshold of 4MB.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Add a threshold callback to dm persistent data space maps.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Add a threshold callback function to the persistent data space map
interface for a subsequent patch to use.

dm-thin and dm-cache are interested in knowing when they're getting
low on metadata or data blocks.  This patch introduces a new method
for registering a callback against a threshold.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>