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diff --git a/Documentation/nvdimm/nvdimm.txt b/Documentation/nvdimm/nvdimm.txt deleted file mode 100644 index e894de69915a..000000000000 --- a/Documentation/nvdimm/nvdimm.txt +++ /dev/null @@ -1,815 +0,0 @@ - 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 | - +---------+ +--------------+ +---------------+------+ - - |