linux/drivers/target/Kconfig
Andy Grover 7c9e7a6fe1 target: Add a user-passthrough backstore
Add a LIO storage engine that presents commands to userspace for execution.
This would allow more complex backstores to be implemented out-of-kernel,
and also make experimentation a-la FUSE (but at the SCSI level -- "SUSE"?)
possible.

It uses a mmap()able UIO device per LUN to share a command ring and data
area. The commands are raw SCSI CDBs and iovs for in/out data. The command
ring is also reused for returning scsi command status and optional sense
data.

This implementation is based on Shaohua Li's earlier version but heavily
modified. Differences include:

* Shared memory allocated by kernel, not locked-down user pages
* Single ring for command request and response
* Offsets instead of embedded pointers
* Generic SCSI CDB passthrough instead of per-cmd specialization in ring
  format.
* Uses UIO device instead of anon_file passed in mailbox.
* Optional in-kernel handling of some commands.

The main reason for these differences is to permit greater resiliency
if the user process dies or hangs.

Things not yet implemented (on purpose):

* Zero copy. The data area is flexible enough to allow page flipping or
  backend-allocated pages to be used by fabrics, but it's not clear these
  are performance wins. Can come later.
* Out-of-order command completion by userspace. Possible to add by just
  allowing userspace to change cmd_id in rsp cmd entries, but currently
  not supported.
* No locks between kernel cmd submission and completion routines. Sounds
  like it's possible, but this can come later.
* Sparse allocation of mmaped area. Current code vmallocs the whole thing.
  If the mapped area was larger and not fully mapped then the driver would
  have more freedom to change cmd and data area sizes based on demand.

Current code open issues:

* The use of idrs may be overkill -- we maybe can replace them with a
  simple counter to generate cmd_ids, and a hash table to get a cmd_id's
  associated pointer.
* Use of a free-running counter for cmd ring instead of explicit modulo
  math. This would require power-of-2 cmd ring size.

(Add kconfig depends NET - Randy)

Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
2014-10-03 11:15:20 -07:00

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menuconfig TARGET_CORE
tristate "Generic Target Core Mod (TCM) and ConfigFS Infrastructure"
depends on SCSI && BLOCK
select CONFIGFS_FS
select CRC_T10DIF
default n
help
Say Y or M here to enable the TCM Storage Engine and ConfigFS enabled
control path for target_core_mod. This includes built-in TCM RAMDISK
subsystem logic for virtual LUN 0 access
if TARGET_CORE
config TCM_IBLOCK
tristate "TCM/IBLOCK Subsystem Plugin for Linux/BLOCK"
select BLK_DEV_INTEGRITY
help
Say Y here to enable the TCM/IBLOCK subsystem plugin for non-buffered
access to Linux/Block devices using BIO
config TCM_FILEIO
tristate "TCM/FILEIO Subsystem Plugin for Linux/VFS"
help
Say Y here to enable the TCM/FILEIO subsystem plugin for buffered
access to Linux/VFS struct file or struct block_device
config TCM_PSCSI
tristate "TCM/pSCSI Subsystem Plugin for Linux/SCSI"
help
Say Y here to enable the TCM/pSCSI subsystem plugin for non-buffered
passthrough access to Linux/SCSI device
config TCM_USER
tristate "TCM/USER Subsystem Plugin for Linux"
depends on UIO && NET
help
Say Y here to enable the TCM/USER subsystem plugin for a userspace
process to handle requests
source "drivers/target/loopback/Kconfig"
source "drivers/target/tcm_fc/Kconfig"
source "drivers/target/iscsi/Kconfig"
source "drivers/target/sbp/Kconfig"
endif