Backend Interface#

The core of the xNVMe API is encapsulated by a backend interface. The backend interface consists of implementations of the following.

Attributes#

  • name, name of the backend config

  • descr, human-readable description

  • caps, bitmask of capabilities (xnvme_be_cap) used for URI-based config selection

Device#

  • enumerate(), lists devices

  • dev_from_ident(), open of a given device and return a handle

  • dev_close(), close a device handle

Memory#

  • buf_alloc(), allocate buffer usable with commands

  • buf_free(), de-allocate buffers

  • buf_vtophys()

  • buf_realloc()

Asynchronous#

  • cmd_io(), submit an IO-command to a qpair

  • poke(), process completions on a qpair

  • wait(), wait until all outstanding commands are completed

  • init(), initialize a qpair

  • term(), terminate a qpair

  • supported(), informed whether async. commands are supported

Synchronous#

  • cmd_io(), submit an IO-command and wait for its completion

  • cmd_admin(), submit and Admin-command and wait for its completion

  • supported(), inform wether sync. commands are supported

Backend Interface - Implementation#

Each platform defines its available backend configs in a xnvme_platform_<os>.c file, registering them via the g_xnvme_platform structure. A backend config (xnvme_be_config) is a complete recipe combining async, sync, admin, dev, and mem implementations.

Have a look at the existing implementations:

  • lib/platform/<os>/xnvme_platform_<os>.c: platform registration, scan, classify and the list of configs the OS offers

  • lib/platform/<os>/xnvme_platform_<os>_configs.c: the configs that combine implementations from several directories

  • lib/backend/<dir>/: one directory per mechanism, such as liburing, posix or spdk, and one per OS for its own interfaces, such as linux

  • lib/backend/xnvme_be_registry.h: extern declarations for all configs

And the definition of the backend interface in:

  • lib/backend/xnvme_be.h