diff options
Diffstat (limited to 'Documentation/nvdimm')
| -rw-r--r-- | Documentation/nvdimm/btt.txt | 24 | ||||
| -rw-r--r-- | Documentation/nvdimm/nvdimm.txt | 808 |
2 files changed, 825 insertions, 7 deletions
diff --git a/Documentation/nvdimm/btt.txt b/Documentation/nvdimm/btt.txt index 95134d5ec4a0..b91443f577dc 100644 --- a/Documentation/nvdimm/btt.txt +++ b/Documentation/nvdimm/btt.txt @@ -80,9 +80,17 @@ block. Each map entry is 32 bits. The two most significant bits are special flags, and the remaining form the internal block number. Bit Description -31 : TRIM flag - marks if the block was trimmed or discarded -30 : ERROR flag - marks an error block. Cleared on write. -29 - 0 : Mappings to internal 'postmap' blocks +31 - 30 : Error and Zero flags - Used in the following way: + Bit Description + 31 30 + ----------------------------------------------------------------------- + 00 Initial state. Reads return zeroes; Premap = Postmap + 01 Zero state: Reads return zeroes + 10 Error state: Reads fail; Writes clear 'E' bit + 11 Normal Block – has valid postmap + + +29 - 0 : Mappings to internal 'postmap' blocks Some of the terminology that will be subsequently used: @@ -127,10 +135,11 @@ old_map': alternate old postmap entry new_map': alternate new postmap entry seq' : alternate sequence number. -Each of the above fields is 32-bit, making one entry 16 bytes. Flog updates are +Each of the above fields is 32-bit, making one entry 32 bytes. Entries are also +padded to 64 bytes to avoid cache line sharing or aliasing. Flog updates are done such that for any entry being written, it: a. overwrites the 'old' section in the entry based on sequence numbers -b. writes the new entry such that the sequence number is written last. +b. writes the 'new' section such that the sequence number is written last. c. The concept of lanes @@ -141,8 +150,9 @@ concurrently, 'nlanes' is the number of IOs the BTT device as a whole can process. nlanes = min(nfree, num_cpus) A lane number is obtained at the start of any IO, and is used for indexing into -all the on-disk and in-memory data structures for the duration of the IO. It is -protected by a spinlock. +all the on-disk and in-memory data structures for the duration of the IO. If +there are more CPUs than the max number of available lanes, than lanes are +protected by spinlocks. d. In-memory data structure: Read Tracking Table (RTT) diff --git a/Documentation/nvdimm/nvdimm.txt b/Documentation/nvdimm/nvdimm.txt new file mode 100644 index 000000000000..197a0b6b0582 --- /dev/null +++ b/Documentation/nvdimm/nvdimm.txt @@ -0,0 +1,808 @@ + 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. + +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 all access just one DIMM. + Multiple windows 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 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 this RAS problem, 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 + 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 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 below + 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 orBLK-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 4 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 + as 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 | + +---------+ +--------------+ +---------------+------+ + + |