Backends

liblightnvm hides the implementation of operating system interaction from the user. That is, the implementation of the nvm_cmd_* interface, which is available in the public C API, is delegated at runtime to a backend implementation.

Backend Name	Identifier
NVM_BE_IOCTL	0x1
NVM_BE_LBD	0x2
NVM_BE_SPDK	0x4

By default liblightnvm goes through the available backends in the order as listed above and chooses to use the first backend capable of opening a device without error.

The user can choose to use a specific backend by providing the backend identifier. When using the CLI, this is done by setting the environment variable NVM_CLI_BE_ID e.g.:

NVM_CLI_BE_ID=0x1 nvm_dev info /dev/nvme0n1

# Device information -- nvm_dev_pr
dev_attr:
  verid: 0x02
  be_id: 0x01
  name: 'nvme0n1'
  path: '/dev/nvme0n1'
  fd: 3
  ssw: 12
  mccap: 00000000000000000000000000000001
  pmode: 'SNGL'
  erase_naddrs_max: 64
  read_naddrs_max: 64
  write_naddrs_max: 64
  meta_mode: 0
  bbts_cached: 0
  bbts_cached: 00000000
  quirks: 00000000
dev_geo:
  verid: 0x02
  npugrp: 8
  npunit: 4
  nchunk: 1474
  nsectr: 6144
  nbytes: 4096
  nbytes_oob: 16
  tbytes: 1187021586432
  tmbytes: 1132032
dev_ppaf: ~
dev_ppaf_mask: ~
dev_lbaf:
  pugrp: 3
  punit: 2
  chunk: 11
  sectr: 13
dev_lbaz:
  pugrp: 26
  punit: 24
  chunk: 13
  sectr: 0
dev_lbam:
  pugrp:  '0000000000000000000000000000000000011100000000000000000000000000'
  punit:  '0000000000000000000000000000000000000011000000000000000000000000'
  chunk:  '0000000000000000000000000000000000000000111111111110000000000000'
  sectr:  '0000000000000000000000000000000000000000000000000001111111111111'

Or when using the C API, by providing the backend identifier to function nvm_dev_openf.