816 lines
31 KiB
Plaintext
Executable file
816 lines
31 KiB
Plaintext
Executable file
LIBNVDIMM: Non-Volatile Devices
|
|
libnvdimm - kernel / libndctl - userspace helper library
|
|
linux-nvdimm@lists.01.org
|
|
v13
|
|
|
|
|
|
Glossary
|
|
Overview
|
|
Supporting Documents
|
|
Git Trees
|
|
LIBNVDIMM PMEM and BLK
|
|
Why BLK?
|
|
PMEM vs BLK
|
|
BLK-REGIONs, PMEM-REGIONs, Atomic Sectors, and DAX
|
|
Example NVDIMM Platform
|
|
LIBNVDIMM Kernel Device Model and LIBNDCTL Userspace API
|
|
LIBNDCTL: Context
|
|
libndctl: instantiate a new library context example
|
|
LIBNVDIMM/LIBNDCTL: Bus
|
|
libnvdimm: control class device in /sys/class
|
|
libnvdimm: bus
|
|
libndctl: bus enumeration example
|
|
LIBNVDIMM/LIBNDCTL: DIMM (NMEM)
|
|
libnvdimm: DIMM (NMEM)
|
|
libndctl: DIMM enumeration example
|
|
LIBNVDIMM/LIBNDCTL: Region
|
|
libnvdimm: region
|
|
libndctl: region enumeration example
|
|
Why Not Encode the Region Type into the Region Name?
|
|
How Do I Determine the Major Type of a Region?
|
|
LIBNVDIMM/LIBNDCTL: Namespace
|
|
libnvdimm: namespace
|
|
libndctl: namespace enumeration example
|
|
libndctl: namespace creation example
|
|
Why the Term "namespace"?
|
|
LIBNVDIMM/LIBNDCTL: Block Translation Table "btt"
|
|
libnvdimm: btt layout
|
|
libndctl: btt creation example
|
|
Summary LIBNDCTL Diagram
|
|
|
|
|
|
Glossary
|
|
--------
|
|
|
|
PMEM: A system-physical-address range where writes are persistent. A
|
|
block device composed of PMEM is capable of DAX. A PMEM address range
|
|
may span an interleave of several DIMMs.
|
|
|
|
BLK: A set of one or more programmable memory mapped apertures provided
|
|
by a DIMM to access its media. This indirection precludes the
|
|
performance benefit of interleaving, but enables DIMM-bounded failure
|
|
modes.
|
|
|
|
DPA: DIMM Physical Address, is a DIMM-relative offset. With one DIMM in
|
|
the system there would be a 1:1 system-physical-address:DPA association.
|
|
Once more DIMMs are added a memory controller interleave must be
|
|
decoded to determine the DPA associated with a given
|
|
system-physical-address. BLK capacity always has a 1:1 relationship
|
|
with a single-DIMM's DPA range.
|
|
|
|
DAX: File system extensions to bypass the page cache and block layer to
|
|
mmap persistent memory, from a PMEM block device, directly into a
|
|
process address space.
|
|
|
|
DSM: Device Specific Method: ACPI method to to control specific
|
|
device - in this case the firmware.
|
|
|
|
DCR: NVDIMM Control Region Structure defined in ACPI 6 Section 5.2.25.5.
|
|
It defines a vendor-id, device-id, and interface format for a given DIMM.
|
|
|
|
BTT: Block Translation Table: Persistent memory is byte addressable.
|
|
Existing software may have an expectation that the power-fail-atomicity
|
|
of writes is at least one sector, 512 bytes. The BTT is an indirection
|
|
table with atomic update semantics to front a PMEM/BLK block device
|
|
driver and present arbitrary atomic sector sizes.
|
|
|
|
LABEL: Metadata stored on a DIMM device that partitions and identifies
|
|
(persistently names) storage between PMEM and BLK. It also partitions
|
|
BLK storage to host BTTs with different parameters per BLK-partition.
|
|
Note that traditional partition tables, GPT/MBR, are layered on top of a
|
|
BLK or PMEM device.
|
|
|
|
|
|
Overview
|
|
--------
|
|
|
|
The LIBNVDIMM subsystem provides support for three types of NVDIMMs, namely,
|
|
PMEM, BLK, and NVDIMM devices that can simultaneously support both PMEM
|
|
and BLK mode access. These three modes of operation are described by
|
|
the "NVDIMM Firmware Interface Table" (NFIT) in ACPI 6. While the LIBNVDIMM
|
|
implementation is generic and supports pre-NFIT platforms, it was guided
|
|
by the superset of capabilities need to support this ACPI 6 definition
|
|
for NVDIMM resources. The bulk of the kernel implementation is in place
|
|
to handle the case where DPA accessible via PMEM is aliased with DPA
|
|
accessible via BLK. When that occurs a LABEL is needed to reserve DPA
|
|
for exclusive access via one mode a time.
|
|
|
|
Supporting Documents
|
|
ACPI 6: http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf
|
|
NVDIMM Namespace: http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
|
|
DSM Interface Example: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
|
|
Driver Writer's Guide: http://pmem.io/documents/NVDIMM_Driver_Writers_Guide.pdf
|
|
|
|
Git Trees
|
|
LIBNVDIMM: https://git.kernel.org/cgit/linux/kernel/git/djbw/nvdimm.git
|
|
LIBNDCTL: https://github.com/pmem/ndctl.git
|
|
PMEM: https://github.com/01org/prd
|
|
|
|
|
|
LIBNVDIMM PMEM and BLK
|
|
------------------
|
|
|
|
Prior to the arrival of the NFIT, non-volatile memory was described to a
|
|
system in various ad-hoc ways. Usually only the bare minimum was
|
|
provided, namely, a single system-physical-address range where writes
|
|
are expected to be durable after a system power loss. Now, the NFIT
|
|
specification standardizes not only the description of PMEM, but also
|
|
BLK and platform message-passing entry points for control and
|
|
configuration.
|
|
|
|
For each NVDIMM access method (PMEM, BLK), LIBNVDIMM provides a block
|
|
device driver:
|
|
|
|
1. PMEM (nd_pmem.ko): Drives a system-physical-address range. This
|
|
range is contiguous in system memory and may be interleaved (hardware
|
|
memory controller striped) across multiple DIMMs. When interleaved the
|
|
platform may optionally provide details of which DIMMs are participating
|
|
in the interleave.
|
|
|
|
Note that while LIBNVDIMM describes system-physical-address ranges that may
|
|
alias with BLK access as ND_NAMESPACE_PMEM ranges and those without
|
|
alias as ND_NAMESPACE_IO ranges, to the nd_pmem driver there is no
|
|
distinction. The different device-types are an implementation detail
|
|
that userspace can exploit to implement policies like "only interface
|
|
with address ranges from certain DIMMs". It is worth noting that when
|
|
aliasing is present and a DIMM lacks a label, then no block device can
|
|
be created by default as userspace needs to do at least one allocation
|
|
of DPA to the PMEM range. In contrast ND_NAMESPACE_IO ranges, once
|
|
registered, can be immediately attached to nd_pmem.
|
|
|
|
2. BLK (nd_blk.ko): This driver performs I/O using a set of platform
|
|
defined apertures. A set of apertures will access just one DIMM.
|
|
Multiple windows (apertures) allow multiple concurrent accesses, much like
|
|
tagged-command-queuing, and would likely be used by different threads or
|
|
different CPUs.
|
|
|
|
The NFIT specification defines a standard format for a BLK-aperture, but
|
|
the spec also allows for vendor specific layouts, and non-NFIT BLK
|
|
implementations may have other designs for BLK I/O. For this reason
|
|
"nd_blk" calls back into platform-specific code to perform the I/O.
|
|
One such implementation is defined in the "Driver Writer's Guide" and "DSM
|
|
Interface Example".
|
|
|
|
|
|
Why BLK?
|
|
--------
|
|
|
|
While PMEM provides direct byte-addressable CPU-load/store access to
|
|
NVDIMM storage, it does not provide the best system RAS (recovery,
|
|
availability, and serviceability) model. An access to a corrupted
|
|
system-physical-address address causes a CPU exception while an access
|
|
to a corrupted address through an BLK-aperture causes that block window
|
|
to raise an error status in a register. The latter is more aligned with
|
|
the standard error model that host-bus-adapter attached disks present.
|
|
Also, if an administrator ever wants to replace a memory it is easier to
|
|
service a system at DIMM module boundaries. Compare this to PMEM where
|
|
data could be interleaved in an opaque hardware specific manner across
|
|
several DIMMs.
|
|
|
|
PMEM vs BLK
|
|
BLK-apertures solve these RAS problems, but their presence is also the
|
|
major contributing factor to the complexity of the ND subsystem. They
|
|
complicate the implementation because PMEM and BLK alias in DPA space.
|
|
Any given DIMM's DPA-range may contribute to one or more
|
|
system-physical-address sets of interleaved DIMMs, *and* may also be
|
|
accessed in its entirety through its BLK-aperture. Accessing a DPA
|
|
through a system-physical-address while simultaneously accessing the
|
|
same DPA through a BLK-aperture has undefined results. For this reason,
|
|
DIMMs with this dual interface configuration include a DSM function to
|
|
store/retrieve a LABEL. The LABEL effectively partitions the DPA-space
|
|
into exclusive system-physical-address and BLK-aperture accessible
|
|
regions. For simplicity a DIMM is allowed a PMEM "region" per each
|
|
interleave set in which it is a member. The remaining DPA space can be
|
|
carved into an arbitrary number of BLK devices with discontiguous
|
|
extents.
|
|
|
|
BLK-REGIONs, PMEM-REGIONs, Atomic Sectors, and DAX
|
|
--------------------------------------------------
|
|
|
|
One of the few
|
|
reasons to allow multiple BLK namespaces per REGION is so that each
|
|
BLK-namespace can be configured with a BTT with unique atomic sector
|
|
sizes. While a PMEM device can host a BTT the LABEL specification does
|
|
not provide for a sector size to be specified for a PMEM namespace.
|
|
This is due to the expectation that the primary usage model for PMEM is
|
|
via DAX, and the BTT is incompatible with DAX. However, for the cases
|
|
where an application or filesystem still needs atomic sector update
|
|
guarantees it can register a BTT on a PMEM device or partition. See
|
|
LIBNVDIMM/NDCTL: Block Translation Table "btt"
|
|
|
|
|
|
Example NVDIMM Platform
|
|
-----------------------
|
|
|
|
For the remainder of this document the following diagram will be
|
|
referenced for any example sysfs layouts.
|
|
|
|
|
|
(a) (b) DIMM BLK-REGION
|
|
+-------------------+--------+--------+--------+
|
|
+------+ | pm0.0 | blk2.0 | pm1.0 | blk2.1 | 0 region2
|
|
| imc0 +--+- - - region0- - - +--------+ +--------+
|
|
+--+---+ | pm0.0 | blk3.0 | pm1.0 | blk3.1 | 1 region3
|
|
| +-------------------+--------v v--------+
|
|
+--+---+ | |
|
|
| cpu0 | region1
|
|
+--+---+ | |
|
|
| +----------------------------^ ^--------+
|
|
+--+---+ | blk4.0 | pm1.0 | blk4.0 | 2 region4
|
|
| imc1 +--+----------------------------| +--------+
|
|
+------+ | blk5.0 | pm1.0 | blk5.0 | 3 region5
|
|
+----------------------------+--------+--------+
|
|
|
|
In this platform we have four DIMMs and two memory controllers in one
|
|
socket. Each unique interface (BLK or PMEM) to DPA space is identified
|
|
by a region device with a dynamically assigned id (REGION0 - REGION5).
|
|
|
|
1. The first portion of DIMM0 and DIMM1 are interleaved as REGION0. A
|
|
single PMEM namespace is created in the REGION0-SPA-range that spans most
|
|
of DIMM0 and DIMM1 with a user-specified name of "pm0.0". Some of that
|
|
interleaved system-physical-address range is reclaimed as BLK-aperture
|
|
accessed space starting at DPA-offset (a) into each DIMM. In that
|
|
reclaimed space we create two BLK-aperture "namespaces" from REGION2 and
|
|
REGION3 where "blk2.0" and "blk3.0" are just human readable names that
|
|
could be set to any user-desired name in the LABEL.
|
|
|
|
2. In the last portion of DIMM0 and DIMM1 we have an interleaved
|
|
system-physical-address range, REGION1, that spans those two DIMMs as
|
|
well as DIMM2 and DIMM3. Some of REGION1 is allocated to a PMEM namespace
|
|
named "pm1.0", the rest is reclaimed in 4 BLK-aperture namespaces (for
|
|
each DIMM in the interleave set), "blk2.1", "blk3.1", "blk4.0", and
|
|
"blk5.0".
|
|
|
|
3. The portion of DIMM2 and DIMM3 that do not participate in the REGION1
|
|
interleaved system-physical-address range (i.e. the DPA address past
|
|
offset (b) are also included in the "blk4.0" and "blk5.0" namespaces.
|
|
Note, that this example shows that BLK-aperture namespaces don't need to
|
|
be contiguous in DPA-space.
|
|
|
|
This bus is provided by the kernel under the device
|
|
/sys/devices/platform/nfit_test.0 when CONFIG_NFIT_TEST is enabled and
|
|
the nfit_test.ko module is loaded. This not only test LIBNVDIMM but the
|
|
acpi_nfit.ko driver as well.
|
|
|
|
|
|
LIBNVDIMM Kernel Device Model and LIBNDCTL Userspace API
|
|
----------------------------------------------------
|
|
|
|
What follows is a description of the LIBNVDIMM sysfs layout and a
|
|
corresponding object hierarchy diagram as viewed through the LIBNDCTL
|
|
API. The example sysfs paths and diagrams are relative to the Example
|
|
NVDIMM Platform which is also the LIBNVDIMM bus used in the LIBNDCTL unit
|
|
test.
|
|
|
|
LIBNDCTL: Context
|
|
Every API call in the LIBNDCTL library requires a context that holds the
|
|
logging parameters and other library instance state. The library is
|
|
based on the libabc template:
|
|
https://git.kernel.org/cgit/linux/kernel/git/kay/libabc.git
|
|
|
|
LIBNDCTL: instantiate a new library context example
|
|
|
|
struct ndctl_ctx *ctx;
|
|
|
|
if (ndctl_new(&ctx) == 0)
|
|
return ctx;
|
|
else
|
|
return NULL;
|
|
|
|
LIBNVDIMM/LIBNDCTL: Bus
|
|
-------------------
|
|
|
|
A bus has a 1:1 relationship with an NFIT. The current expectation for
|
|
ACPI based systems is that there is only ever one platform-global NFIT.
|
|
That said, it is trivial to register multiple NFITs, the specification
|
|
does not preclude it. The infrastructure supports multiple busses and
|
|
we we use this capability to test multiple NFIT configurations in the
|
|
unit test.
|
|
|
|
LIBNVDIMM: control class device in /sys/class
|
|
|
|
This character device accepts DSM messages to be passed to DIMM
|
|
identified by its NFIT handle.
|
|
|
|
/sys/class/nd/ndctl0
|
|
|-- dev
|
|
|-- device -> ../../../ndbus0
|
|
|-- subsystem -> ../../../../../../../class/nd
|
|
|
|
|
|
|
|
LIBNVDIMM: bus
|
|
|
|
struct nvdimm_bus *nvdimm_bus_register(struct device *parent,
|
|
struct nvdimm_bus_descriptor *nfit_desc);
|
|
|
|
/sys/devices/platform/nfit_test.0/ndbus0
|
|
|-- commands
|
|
|-- nd
|
|
|-- nfit
|
|
|-- nmem0
|
|
|-- nmem1
|
|
|-- nmem2
|
|
|-- nmem3
|
|
|-- power
|
|
|-- provider
|
|
|-- region0
|
|
|-- region1
|
|
|-- region2
|
|
|-- region3
|
|
|-- region4
|
|
|-- region5
|
|
|-- uevent
|
|
`-- wait_probe
|
|
|
|
LIBNDCTL: bus enumeration example
|
|
Find the bus handle that describes the bus from Example NVDIMM Platform
|
|
|
|
static struct ndctl_bus *get_bus_by_provider(struct ndctl_ctx *ctx,
|
|
const char *provider)
|
|
{
|
|
struct ndctl_bus *bus;
|
|
|
|
ndctl_bus_foreach(ctx, bus)
|
|
if (strcmp(provider, ndctl_bus_get_provider(bus)) == 0)
|
|
return bus;
|
|
|
|
return NULL;
|
|
}
|
|
|
|
bus = get_bus_by_provider(ctx, "nfit_test.0");
|
|
|
|
|
|
LIBNVDIMM/LIBNDCTL: DIMM (NMEM)
|
|
---------------------------
|
|
|
|
The DIMM device provides a character device for sending commands to
|
|
hardware, and it is a container for LABELs. If the DIMM is defined by
|
|
NFIT then an optional 'nfit' attribute sub-directory is available to add
|
|
NFIT-specifics.
|
|
|
|
Note that the kernel device name for "DIMMs" is "nmemX". The NFIT
|
|
describes these devices via "Memory Device to System Physical Address
|
|
Range Mapping Structure", and there is no requirement that they actually
|
|
be physical DIMMs, so we use a more generic name.
|
|
|
|
LIBNVDIMM: DIMM (NMEM)
|
|
|
|
struct nvdimm *nvdimm_create(struct nvdimm_bus *nvdimm_bus, void *provider_data,
|
|
const struct attribute_group **groups, unsigned long flags,
|
|
unsigned long *dsm_mask);
|
|
|
|
/sys/devices/platform/nfit_test.0/ndbus0
|
|
|-- nmem0
|
|
| |-- available_slots
|
|
| |-- commands
|
|
| |-- dev
|
|
| |-- devtype
|
|
| |-- driver -> ../../../../../bus/nd/drivers/nvdimm
|
|
| |-- modalias
|
|
| |-- nfit
|
|
| | |-- device
|
|
| | |-- format
|
|
| | |-- handle
|
|
| | |-- phys_id
|
|
| | |-- rev_id
|
|
| | |-- serial
|
|
| | `-- vendor
|
|
| |-- state
|
|
| |-- subsystem -> ../../../../../bus/nd
|
|
| `-- uevent
|
|
|-- nmem1
|
|
[..]
|
|
|
|
|
|
LIBNDCTL: DIMM enumeration example
|
|
|
|
Note, in this example we are assuming NFIT-defined DIMMs which are
|
|
identified by an "nfit_handle" a 32-bit value where:
|
|
Bit 3:0 DIMM number within the memory channel
|
|
Bit 7:4 memory channel number
|
|
Bit 11:8 memory controller ID
|
|
Bit 15:12 socket ID (within scope of a Node controller if node controller is present)
|
|
Bit 27:16 Node Controller ID
|
|
Bit 31:28 Reserved
|
|
|
|
static struct ndctl_dimm *get_dimm_by_handle(struct ndctl_bus *bus,
|
|
unsigned int handle)
|
|
{
|
|
struct ndctl_dimm *dimm;
|
|
|
|
ndctl_dimm_foreach(bus, dimm)
|
|
if (ndctl_dimm_get_handle(dimm) == handle)
|
|
return dimm;
|
|
|
|
return NULL;
|
|
}
|
|
|
|
#define DIMM_HANDLE(n, s, i, c, d) \
|
|
(((n & 0xfff) << 16) | ((s & 0xf) << 12) | ((i & 0xf) << 8) \
|
|
| ((c & 0xf) << 4) | (d & 0xf))
|
|
|
|
dimm = get_dimm_by_handle(bus, DIMM_HANDLE(0, 0, 0, 0, 0));
|
|
|
|
LIBNVDIMM/LIBNDCTL: Region
|
|
----------------------
|
|
|
|
A generic REGION device is registered for each PMEM range or BLK-aperture
|
|
set. Per the example there are 6 regions: 2 PMEM and 4 BLK-aperture
|
|
sets on the "nfit_test.0" bus. The primary role of regions are to be a
|
|
container of "mappings". A mapping is a tuple of <DIMM,
|
|
DPA-start-offset, length>.
|
|
|
|
LIBNVDIMM provides a built-in driver for these REGION devices. This driver
|
|
is responsible for reconciling the aliased DPA mappings across all
|
|
regions, parsing the LABEL, if present, and then emitting NAMESPACE
|
|
devices with the resolved/exclusive DPA-boundaries for the nd_pmem or
|
|
nd_blk device driver to consume.
|
|
|
|
In addition to the generic attributes of "mapping"s, "interleave_ways"
|
|
and "size" the REGION device also exports some convenience attributes.
|
|
"nstype" indicates the integer type of namespace-device this region
|
|
emits, "devtype" duplicates the DEVTYPE variable stored by udev at the
|
|
'add' event, "modalias" duplicates the MODALIAS variable stored by udev
|
|
at the 'add' event, and finally, the optional "spa_index" is provided in
|
|
the case where the region is defined by a SPA.
|
|
|
|
LIBNVDIMM: region
|
|
|
|
struct nd_region *nvdimm_pmem_region_create(struct nvdimm_bus *nvdimm_bus,
|
|
struct nd_region_desc *ndr_desc);
|
|
struct nd_region *nvdimm_blk_region_create(struct nvdimm_bus *nvdimm_bus,
|
|
struct nd_region_desc *ndr_desc);
|
|
|
|
/sys/devices/platform/nfit_test.0/ndbus0
|
|
|-- region0
|
|
| |-- available_size
|
|
| |-- btt0
|
|
| |-- btt_seed
|
|
| |-- devtype
|
|
| |-- driver -> ../../../../../bus/nd/drivers/nd_region
|
|
| |-- init_namespaces
|
|
| |-- mapping0
|
|
| |-- mapping1
|
|
| |-- mappings
|
|
| |-- modalias
|
|
| |-- namespace0.0
|
|
| |-- namespace_seed
|
|
| |-- numa_node
|
|
| |-- nfit
|
|
| | `-- spa_index
|
|
| |-- nstype
|
|
| |-- set_cookie
|
|
| |-- size
|
|
| |-- subsystem -> ../../../../../bus/nd
|
|
| `-- uevent
|
|
|-- region1
|
|
[..]
|
|
|
|
LIBNDCTL: region enumeration example
|
|
|
|
Sample region retrieval routines based on NFIT-unique data like
|
|
"spa_index" (interleave set id) for PMEM and "nfit_handle" (dimm id) for
|
|
BLK.
|
|
|
|
static struct ndctl_region *get_pmem_region_by_spa_index(struct ndctl_bus *bus,
|
|
unsigned int spa_index)
|
|
{
|
|
struct ndctl_region *region;
|
|
|
|
ndctl_region_foreach(bus, region) {
|
|
if (ndctl_region_get_type(region) != ND_DEVICE_REGION_PMEM)
|
|
continue;
|
|
if (ndctl_region_get_spa_index(region) == spa_index)
|
|
return region;
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
static struct ndctl_region *get_blk_region_by_dimm_handle(struct ndctl_bus *bus,
|
|
unsigned int handle)
|
|
{
|
|
struct ndctl_region *region;
|
|
|
|
ndctl_region_foreach(bus, region) {
|
|
struct ndctl_mapping *map;
|
|
|
|
if (ndctl_region_get_type(region) != ND_DEVICE_REGION_BLOCK)
|
|
continue;
|
|
ndctl_mapping_foreach(region, map) {
|
|
struct ndctl_dimm *dimm = ndctl_mapping_get_dimm(map);
|
|
|
|
if (ndctl_dimm_get_handle(dimm) == handle)
|
|
return region;
|
|
}
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
|
|
Why Not Encode the Region Type into the Region Name?
|
|
----------------------------------------------------
|
|
|
|
At first glance it seems since NFIT defines just PMEM and BLK interface
|
|
types that we should simply name REGION devices with something derived
|
|
from those type names. However, the ND subsystem explicitly keeps the
|
|
REGION name generic and expects userspace to always consider the
|
|
region-attributes for four reasons:
|
|
|
|
1. There are already more than two REGION and "namespace" types. For
|
|
PMEM there are two subtypes. As mentioned previously we have PMEM where
|
|
the constituent DIMM devices are known and anonymous PMEM. For BLK
|
|
regions the NFIT specification already anticipates vendor specific
|
|
implementations. The exact distinction of what a region contains is in
|
|
the region-attributes not the region-name or the region-devtype.
|
|
|
|
2. A region with zero child-namespaces is a possible configuration. For
|
|
example, the NFIT allows for a DCR to be published without a
|
|
corresponding BLK-aperture. This equates to a DIMM that can only accept
|
|
control/configuration messages, but no i/o through a descendant block
|
|
device. Again, this "type" is advertised in the attributes ('mappings'
|
|
== 0) and the name does not tell you much.
|
|
|
|
3. What if a third major interface type arises in the future? Outside
|
|
of vendor specific implementations, it's not difficult to envision a
|
|
third class of interface type beyond BLK and PMEM. With a generic name
|
|
for the REGION level of the device-hierarchy old userspace
|
|
implementations can still make sense of new kernel advertised
|
|
region-types. Userspace can always rely on the generic region
|
|
attributes like "mappings", "size", etc and the expected child devices
|
|
named "namespace". This generic format of the device-model hierarchy
|
|
allows the LIBNVDIMM and LIBNDCTL implementations to be more uniform and
|
|
future-proof.
|
|
|
|
4. There are more robust mechanisms for determining the major type of a
|
|
region than a device name. See the next section, How Do I Determine the
|
|
Major Type of a Region?
|
|
|
|
How Do I Determine the Major Type of a Region?
|
|
----------------------------------------------
|
|
|
|
Outside of the blanket recommendation of "use libndctl", or simply
|
|
looking at the kernel header (/usr/include/linux/ndctl.h) to decode the
|
|
"nstype" integer attribute, here are some other options.
|
|
|
|
1. module alias lookup:
|
|
|
|
The whole point of region/namespace device type differentiation is to
|
|
decide which block-device driver will attach to a given LIBNVDIMM namespace.
|
|
One can simply use the modalias to lookup the resulting module. It's
|
|
important to note that this method is robust in the presence of a
|
|
vendor-specific driver down the road. If a vendor-specific
|
|
implementation wants to supplant the standard nd_blk driver it can with
|
|
minimal impact to the rest of LIBNVDIMM.
|
|
|
|
In fact, a vendor may also want to have a vendor-specific region-driver
|
|
(outside of nd_region). For example, if a vendor defined its own LABEL
|
|
format it would need its own region driver to parse that LABEL and emit
|
|
the resulting namespaces. The output from module resolution is more
|
|
accurate than a region-name or region-devtype.
|
|
|
|
2. udev:
|
|
|
|
The kernel "devtype" is registered in the udev database
|
|
# udevadm info --path=/devices/platform/nfit_test.0/ndbus0/region0
|
|
P: /devices/platform/nfit_test.0/ndbus0/region0
|
|
E: DEVPATH=/devices/platform/nfit_test.0/ndbus0/region0
|
|
E: DEVTYPE=nd_pmem
|
|
E: MODALIAS=nd:t2
|
|
E: SUBSYSTEM=nd
|
|
|
|
# udevadm info --path=/devices/platform/nfit_test.0/ndbus0/region4
|
|
P: /devices/platform/nfit_test.0/ndbus0/region4
|
|
E: DEVPATH=/devices/platform/nfit_test.0/ndbus0/region4
|
|
E: DEVTYPE=nd_blk
|
|
E: MODALIAS=nd:t3
|
|
E: SUBSYSTEM=nd
|
|
|
|
...and is available as a region attribute, but keep in mind that the
|
|
"devtype" does not indicate sub-type variations and scripts should
|
|
really be understanding the other attributes.
|
|
|
|
3. type specific attributes:
|
|
|
|
As it currently stands a BLK-aperture region will never have a
|
|
"nfit/spa_index" attribute, but neither will a non-NFIT PMEM region. A
|
|
BLK region with a "mappings" value of 0 is, as mentioned above, a DIMM
|
|
that does not allow I/O. A PMEM region with a "mappings" value of zero
|
|
is a simple system-physical-address range.
|
|
|
|
|
|
LIBNVDIMM/LIBNDCTL: Namespace
|
|
-------------------------
|
|
|
|
A REGION, after resolving DPA aliasing and LABEL specified boundaries,
|
|
surfaces one or more "namespace" devices. The arrival of a "namespace"
|
|
device currently triggers either the nd_blk or nd_pmem driver to load
|
|
and register a disk/block device.
|
|
|
|
LIBNVDIMM: namespace
|
|
Here is a sample layout from the three major types of NAMESPACE where
|
|
namespace0.0 represents DIMM-info-backed PMEM (note that it has a 'uuid'
|
|
attribute), namespace2.0 represents a BLK namespace (note it has a
|
|
'sector_size' attribute) that, and namespace6.0 represents an anonymous
|
|
PMEM namespace (note that has no 'uuid' attribute due to not support a
|
|
LABEL).
|
|
|
|
/sys/devices/platform/nfit_test.0/ndbus0/region0/namespace0.0
|
|
|-- alt_name
|
|
|-- devtype
|
|
|-- dpa_extents
|
|
|-- force_raw
|
|
|-- modalias
|
|
|-- numa_node
|
|
|-- resource
|
|
|-- size
|
|
|-- subsystem -> ../../../../../../bus/nd
|
|
|-- type
|
|
|-- uevent
|
|
`-- uuid
|
|
/sys/devices/platform/nfit_test.0/ndbus0/region2/namespace2.0
|
|
|-- alt_name
|
|
|-- devtype
|
|
|-- dpa_extents
|
|
|-- force_raw
|
|
|-- modalias
|
|
|-- numa_node
|
|
|-- sector_size
|
|
|-- size
|
|
|-- subsystem -> ../../../../../../bus/nd
|
|
|-- type
|
|
|-- uevent
|
|
`-- uuid
|
|
/sys/devices/platform/nfit_test.1/ndbus1/region6/namespace6.0
|
|
|-- block
|
|
| `-- pmem0
|
|
|-- devtype
|
|
|-- driver -> ../../../../../../bus/nd/drivers/pmem
|
|
|-- force_raw
|
|
|-- modalias
|
|
|-- numa_node
|
|
|-- resource
|
|
|-- size
|
|
|-- subsystem -> ../../../../../../bus/nd
|
|
|-- type
|
|
`-- uevent
|
|
|
|
LIBNDCTL: namespace enumeration example
|
|
Namespaces are indexed relative to their parent region, example below.
|
|
These indexes are mostly static from boot to boot, but subsystem makes
|
|
no guarantees in this regard. For a static namespace identifier use its
|
|
'uuid' attribute.
|
|
|
|
static struct ndctl_namespace *get_namespace_by_id(struct ndctl_region *region,
|
|
unsigned int id)
|
|
{
|
|
struct ndctl_namespace *ndns;
|
|
|
|
ndctl_namespace_foreach(region, ndns)
|
|
if (ndctl_namespace_get_id(ndns) == id)
|
|
return ndns;
|
|
|
|
return NULL;
|
|
}
|
|
|
|
LIBNDCTL: namespace creation example
|
|
Idle namespaces are automatically created by the kernel if a given
|
|
region has enough available capacity to create a new namespace.
|
|
Namespace instantiation involves finding an idle namespace and
|
|
configuring it. For the most part the setting of namespace attributes
|
|
can occur in any order, the only constraint is that 'uuid' must be set
|
|
before 'size'. This enables the kernel to track DPA allocations
|
|
internally with a static identifier.
|
|
|
|
static int configure_namespace(struct ndctl_region *region,
|
|
struct ndctl_namespace *ndns,
|
|
struct namespace_parameters *parameters)
|
|
{
|
|
char devname[50];
|
|
|
|
snprintf(devname, sizeof(devname), "namespace%d.%d",
|
|
ndctl_region_get_id(region), paramaters->id);
|
|
|
|
ndctl_namespace_set_alt_name(ndns, devname);
|
|
/* 'uuid' must be set prior to setting size! */
|
|
ndctl_namespace_set_uuid(ndns, paramaters->uuid);
|
|
ndctl_namespace_set_size(ndns, paramaters->size);
|
|
/* unlike pmem namespaces, blk namespaces have a sector size */
|
|
if (parameters->lbasize)
|
|
ndctl_namespace_set_sector_size(ndns, parameters->lbasize);
|
|
ndctl_namespace_enable(ndns);
|
|
}
|
|
|
|
|
|
Why the Term "namespace"?
|
|
|
|
1. Why not "volume" for instance? "volume" ran the risk of confusing
|
|
ND (libnvdimm subsystem) to a volume manager like device-mapper.
|
|
|
|
2. The term originated to describe the sub-devices that can be created
|
|
within a NVME controller (see the nvme specification:
|
|
http://www.nvmexpress.org/specifications/), and NFIT namespaces are
|
|
meant to parallel the capabilities and configurability of
|
|
NVME-namespaces.
|
|
|
|
|
|
LIBNVDIMM/LIBNDCTL: Block Translation Table "btt"
|
|
---------------------------------------------
|
|
|
|
A BTT (design document: http://pmem.io/2014/09/23/btt.html) is a stacked
|
|
block device driver that fronts either the whole block device or a
|
|
partition of a block device emitted by either a PMEM or BLK NAMESPACE.
|
|
|
|
LIBNVDIMM: btt layout
|
|
Every region will start out with at least one BTT device which is the
|
|
seed device. To activate it set the "namespace", "uuid", and
|
|
"sector_size" attributes and then bind the device to the nd_pmem or
|
|
nd_blk driver depending on the region type.
|
|
|
|
/sys/devices/platform/nfit_test.1/ndbus0/region0/btt0/
|
|
|-- namespace
|
|
|-- delete
|
|
|-- devtype
|
|
|-- modalias
|
|
|-- numa_node
|
|
|-- sector_size
|
|
|-- subsystem -> ../../../../../bus/nd
|
|
|-- uevent
|
|
`-- uuid
|
|
|
|
LIBNDCTL: btt creation example
|
|
Similar to namespaces an idle BTT device is automatically created per
|
|
region. Each time this "seed" btt device is configured and enabled a new
|
|
seed is created. Creating a BTT configuration involves two steps of
|
|
finding and idle BTT and assigning it to consume a PMEM or BLK namespace.
|
|
|
|
static struct ndctl_btt *get_idle_btt(struct ndctl_region *region)
|
|
{
|
|
struct ndctl_btt *btt;
|
|
|
|
ndctl_btt_foreach(region, btt)
|
|
if (!ndctl_btt_is_enabled(btt)
|
|
&& !ndctl_btt_is_configured(btt))
|
|
return btt;
|
|
|
|
return NULL;
|
|
}
|
|
|
|
static int configure_btt(struct ndctl_region *region,
|
|
struct btt_parameters *parameters)
|
|
{
|
|
btt = get_idle_btt(region);
|
|
|
|
ndctl_btt_set_uuid(btt, parameters->uuid);
|
|
ndctl_btt_set_sector_size(btt, parameters->sector_size);
|
|
ndctl_btt_set_namespace(btt, parameters->ndns);
|
|
/* turn off raw mode device */
|
|
ndctl_namespace_disable(parameters->ndns);
|
|
/* turn on btt access */
|
|
ndctl_btt_enable(btt);
|
|
}
|
|
|
|
Once instantiated a new inactive btt seed device will appear underneath
|
|
the region.
|
|
|
|
Once a "namespace" is removed from a BTT that instance of the BTT device
|
|
will be deleted or otherwise reset to default values. This deletion is
|
|
only at the device model level. In order to destroy a BTT the "info
|
|
block" needs to be destroyed. Note, that to destroy a BTT the media
|
|
needs to be written in raw mode. By default, the kernel will autodetect
|
|
the presence of a BTT and disable raw mode. This autodetect behavior
|
|
can be suppressed by enabling raw mode for the namespace via the
|
|
ndctl_namespace_set_raw_mode() API.
|
|
|
|
|
|
Summary LIBNDCTL Diagram
|
|
------------------------
|
|
|
|
For the given example above, here is the view of the objects as seen by the
|
|
LIBNDCTL API:
|
|
+---+
|
|
|CTX| +---------+ +--------------+ +---------------+
|
|
+-+-+ +-> REGION0 +---> NAMESPACE0.0 +--> PMEM8 "pm0.0" |
|
|
| | +---------+ +--------------+ +---------------+
|
|
+-------+ | | +---------+ +--------------+ +---------------+
|
|
| DIMM0 <-+ | +-> REGION1 +---> NAMESPACE1.0 +--> PMEM6 "pm1.0" |
|
|
+-------+ | | | +---------+ +--------------+ +---------------+
|
|
| DIMM1 <-+ +-v--+ | +---------+ +--------------+ +---------------+
|
|
+-------+ +-+BUS0+---> REGION2 +-+-> NAMESPACE2.0 +--> ND6 "blk2.0" |
|
|
| DIMM2 <-+ +----+ | +---------+ | +--------------+ +----------------------+
|
|
+-------+ | | +-> NAMESPACE2.1 +--> ND5 "blk2.1" | BTT2 |
|
|
| DIMM3 <-+ | +--------------+ +----------------------+
|
|
+-------+ | +---------+ +--------------+ +---------------+
|
|
+-> REGION3 +-+-> NAMESPACE3.0 +--> ND4 "blk3.0" |
|
|
| +---------+ | +--------------+ +----------------------+
|
|
| +-> NAMESPACE3.1 +--> ND3 "blk3.1" | BTT1 |
|
|
| +--------------+ +----------------------+
|
|
| +---------+ +--------------+ +---------------+
|
|
+-> REGION4 +---> NAMESPACE4.0 +--> ND2 "blk4.0" |
|
|
| +---------+ +--------------+ +---------------+
|
|
| +---------+ +--------------+ +----------------------+
|
|
+-> REGION5 +---> NAMESPACE5.0 +--> ND1 "blk5.0" | BTT0 |
|
|
+---------+ +--------------+ +---------------+------+
|
|
|
|
|