Documentation/scsi/osd.txt - kernel/mindspeed - Git at Google

 The OSD Standard
 ================
 OSD (Object-Based Storage Device) is a T10 SCSI command set that is designed
 to provide efficient operation of input/output logical units that manage the
 allocation, placement, and accessing of variable-size data-storage containers,
 called objects. Objects are intended to contain operating system and application
 constructs. Each object has associated attributes attached to it, which are
 integral part of the object and provide metadata about the object. The standard
 defines some common obligatory attributes, but user attributes can be added as
 needed.

 See: http://www.t10.org/ftp/t10/drafts/osd2/ for the latest draft for OSD 2
 or search the web for "OSD SCSI"

 OSD in the Linux Kernel
 =======================
 osd-initiator:
   The main component of OSD in Kernel is the osd-initiator library. Its main
 user is intended to be the pNFS-over-objects layout driver, which uses objects
 as its back-end data storage. Other clients are the other osd parts listed below.

 osd-uld:
   This is a SCSI ULD that registers for OSD type devices and provides a testing
 platform, both for the in-kernel initiator as well as connected targets. It
 currently has no useful user-mode API, though it could have if need be.

 exofs:
   Is an OSD based Linux file system. It uses the osd-initiator and osd-uld,
 to export a usable file system for users.
 See Documentation/filesystems/exofs.txt for more details

 osd target:
   There are no current plans for an OSD target implementation in kernel. For all
 needs, a user-mode target that is based on the scsi tgt target framework is
 available from Ohio Supercomputer Center (OSC) at:
 http://www.open-osd.org/bin/view/Main/OscOsdProject
 There are several other target implementations. See http://open-osd.org for more
 links.

 Files and Folders
 =================
 This is the complete list of files included in this work:
 include/scsi/
 	osd_initiator.h   Main API for the initiator library
 	osd_types.h	  Common OSD types
 	osd_sec.h	  Security Manager API
 	osd_protocol.h	  Wire definitions of the OSD standard protocol
 	osd_attributes.h  Wire definitions of OSD attributes

 drivers/scsi/osd/
 	osd_initiator.c   OSD-Initiator library implementation
 	osd_uld.c	  The OSD scsi ULD
 	osd_ktest.{h,c}	  In-kernel test suite (called by osd_uld)
 	osd_debug.h	  Some printk macros
 	Makefile	  For both in-tree and out-of-tree compilation
 	Kconfig		  Enables inclusion of the different pieces
 	osd_test.c	  User-mode application to call the kernel tests

 The OSD-Initiator Library
 =========================
 osd_initiator is a low level implementation of an osd initiator encoder.
 But even though, it should be intuitive and easy to use. Perhaps over time an
 higher lever will form that automates some of the more common recipes.

 init/fini:
 - osd_dev_init() associates a scsi_device with an osd_dev structure
   and initializes some global pools. This should be done once per scsi_device
   (OSD LUN). The osd_dev structure is needed for calling osd_start_request().

 - osd_dev_fini() cleans up before a osd_dev/scsi_device destruction.

 OSD commands encoding, execution, and decoding of results:

 struct osd_request's is used to iteratively encode an OSD command and carry
 its state throughout execution. Each request goes through these stages:

 a. osd_start_request() allocates the request.

 b. Any of the osd_req_* methods is used to encode a request of the specified
    type.

 c. osd_req_add_{get,set}_attr_* may be called to add get/set attributes to the
    CDB. "List" or "Page" mode can be used exclusively. The attribute-list API
    can be called multiple times on the same request. However, only one
    attribute-page can be read, as mandated by the OSD standard.

 d. osd_finalize_request() computes offsets into the data-in and data-out buffers
    and signs the request using the provided capability key and integrity-
    check parameters.

 e. osd_execute_request() may be called to execute the request via the block
    layer and wait for its completion.  The request can be executed
    asynchronously by calling the block layer API directly.

 f. After execution, osd_req_decode_sense() can be called to decode the request's
    sense information.

 g. osd_req_decode_get_attr() may be called to retrieve osd_add_get_attr_list()
    values.

 h. osd_end_request() must be called to deallocate the request and any resource
    associated with it. Note that osd_end_request cleans up the request at any
    stage and it must always be called after a successful osd_start_request().

 osd_request's structure:

 The OSD standard defines a complex structure of IO segments pointed to by
 members in the CDB. Up to 3 segments can be deployed in the IN-Buffer and up to
 4 in the OUT-Buffer. The ASCII illustration below depicts a secure-read with
 associated get+set of attributes-lists. Other combinations very on the same
 basic theme. From no-segments-used up to all-segments-used.

 |________OSD-CDB__________|
 |                         |
 |read_len (offset=0)     -|---------\
 |                         |         |
 |get_attrs_list_length    |         |
 |get_attrs_list_offset   -|----\    |
 |                         |    |    |
 |retrieved_attrs_alloc_len|    |    |
 |retrieved_attrs_offset  -|----|----|-\
 |                         |    |    | |
 |set_attrs_list_length    |    |    | |
 |set_attrs_list_offset   -|-\  |    | |
 |                         | |  |    | |
 |in_data_integ_offset    -|-|--|----|-|-\
 |out_data_integ_offset   -|-|--|--\ | | |
 \_________________________/ |  |  | | | |
                             |  |  | | | |
 |_______OUT-BUFFER________| |  |  | | | |
 |      Set attr list      |</  |  | | | |
 |                         |    |  | | | |
 |-------------------------|    |  | | | |
 |   Get attr descriptors  |<---/  | | | |
 |                         |       | | | |
 |-------------------------|       | | | |
 |    Out-data integrity   |<------/ | | |
 |                         |         | | |
 \_________________________/         | | |
                                     | | |
 |________IN-BUFFER________|         | | |
 |      In-Data read       |<--------/ | |
 |                         |           | |
 |-------------------------|           | |
 |      Get attr list      |<----------/ |
 |                         |             |
 |-------------------------|             |
 |    In-data integrity    |<------------/
 |                         |
 \_________________________/

 A block device request can carry bidirectional payload by means of associating
 a bidi_read request with a main write-request. Each in/out request is described
 by a chain of BIOs associated with each request.
 The CDB is of a SCSI VARLEN CDB format, as described by OSD standard.
 The OSD standard also mandates alignment restrictions at start of each segment.

 In the code, in struct osd_request, there are two _osd_io_info structures to
 describe the IN/OUT buffers above, two BIOs for the data payload and up to five
 _osd_req_data_segment structures to hold the different segments allocation and
 information.

 Important: We have chosen to disregard the assumption that a BIO-chain (and
 the resulting sg-list) describes a linear memory buffer. Meaning only first and
 last scatter chain can be incomplete and all the middle chains are of PAGE_SIZE.
 For us, a scatter-gather-list, as its name implies and as used by the Networking
 layer, is to describe a vector of buffers that will be transferred to/from the
 wire. It works very well with current iSCSI transport. iSCSI is currently the
 only deployed OSD transport. In the future we anticipate SAS and FC attached OSD
 devices as well.

 The OSD Testing ULD
 ===================
 TODO: More user-mode control on tests.

 Authors, Mailing list
 =====================
 Please communicate with us on any deployment of osd, whether using this code
 or not.

 Any problems, questions, bug reports, lonely OSD nights, please email:
    OSD Dev List <osd-dev@open-osd.org>

 More up-to-date information can be found on:
 http://open-osd.org

 Boaz Harrosh <bharrosh@panasas.com>
 Benny Halevy <bhalevy@panasas.com>

 References
 ==========
 Weber, R., "SCSI Object-Based Storage Device Commands",
 T10/1355-D ANSI/INCITS 400-2004,
 http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf

 Weber, R., "SCSI Object-Based Storage Device Commands -2 (OSD-2)"
 T10/1729-D, Working Draft, rev. 3
 http://www.t10.org/ftp/t10/drafts/osd2/osd2r03.pdf
	The OSD Standard
	================
	OSD (Object-Based Storage Device) is a T10 SCSI command set that is designed
	to provide efficient operation of input/output logical units that manage the
	allocation, placement, and accessing of variable-size data-storage containers,
	called objects. Objects are intended to contain operating system and application
	constructs. Each object has associated attributes attached to it, which are
	integral part of the object and provide metadata about the object. The standard
	defines some common obligatory attributes, but user attributes can be added as
	needed.

	See: http://www.t10.org/ftp/t10/drafts/osd2/ for the latest draft for OSD 2
	or search the web for "OSD SCSI"

	OSD in the Linux Kernel
	=======================
	osd-initiator:
	The main component of OSD in Kernel is the osd-initiator library. Its main
	user is intended to be the pNFS-over-objects layout driver, which uses objects
	as its back-end data storage. Other clients are the other osd parts listed below.

	osd-uld:
	This is a SCSI ULD that registers for OSD type devices and provides a testing
	platform, both for the in-kernel initiator as well as connected targets. It
	currently has no useful user-mode API, though it could have if need be.

	exofs:
	Is an OSD based Linux file system. It uses the osd-initiator and osd-uld,
	to export a usable file system for users.
	See Documentation/filesystems/exofs.txt for more details

	osd target:
	There are no current plans for an OSD target implementation in kernel. For all
	needs, a user-mode target that is based on the scsi tgt target framework is
	available from Ohio Supercomputer Center (OSC) at:
	http://www.open-osd.org/bin/view/Main/OscOsdProject
	There are several other target implementations. See http://open-osd.org for more
	links.

	Files and Folders
	=================
	This is the complete list of files included in this work:
	include/scsi/
	osd_initiator.h Main API for the initiator library
	osd_types.h Common OSD types
	osd_sec.h Security Manager API
	osd_protocol.h Wire definitions of the OSD standard protocol
	osd_attributes.h Wire definitions of OSD attributes

	drivers/scsi/osd/
	osd_initiator.c OSD-Initiator library implementation
	osd_uld.c The OSD scsi ULD
	osd_ktest.{h,c} In-kernel test suite (called by osd_uld)
	osd_debug.h Some printk macros
	Makefile For both in-tree and out-of-tree compilation
	Kconfig Enables inclusion of the different pieces
	osd_test.c User-mode application to call the kernel tests

	The OSD-Initiator Library
	=========================
	osd_initiator is a low level implementation of an osd initiator encoder.
	But even though, it should be intuitive and easy to use. Perhaps over time an
	higher lever will form that automates some of the more common recipes.

	init/fini:
	- osd_dev_init() associates a scsi_device with an osd_dev structure
	and initializes some global pools. This should be done once per scsi_device
	(OSD LUN). The osd_dev structure is needed for calling osd_start_request().

	- osd_dev_fini() cleans up before a osd_dev/scsi_device destruction.

	OSD commands encoding, execution, and decoding of results:

	struct osd_request's is used to iteratively encode an OSD command and carry
	its state throughout execution. Each request goes through these stages:

	a. osd_start_request() allocates the request.

	b. Any of the osd_req_* methods is used to encode a request of the specified
	type.

	c. osd_req_add_{get,set}_attr_* may be called to add get/set attributes to the
	CDB. "List" or "Page" mode can be used exclusively. The attribute-list API
	can be called multiple times on the same request. However, only one
	attribute-page can be read, as mandated by the OSD standard.

	d. osd_finalize_request() computes offsets into the data-in and data-out buffers
	and signs the request using the provided capability key and integrity-
	check parameters.

	e. osd_execute_request() may be called to execute the request via the block
	layer and wait for its completion. The request can be executed
	asynchronously by calling the block layer API directly.

	f. After execution, osd_req_decode_sense() can be called to decode the request's
	sense information.

	g. osd_req_decode_get_attr() may be called to retrieve osd_add_get_attr_list()
	values.

	h. osd_end_request() must be called to deallocate the request and any resource
	associated with it. Note that osd_end_request cleans up the request at any
	stage and it must always be called after a successful osd_start_request().

	osd_request's structure:

	The OSD standard defines a complex structure of IO segments pointed to by
	members in the CDB. Up to 3 segments can be deployed in the IN-Buffer and up to
	4 in the OUT-Buffer. The ASCII illustration below depicts a secure-read with
	associated get+set of attributes-lists. Other combinations very on the same
	basic theme. From no-segments-used up to all-segments-used.

	\|________OSD-CDB__________\|
	\| \|
	\|read_len (offset=0) -\|---------\
	\| \| \|
	\|get_attrs_list_length \| \|
	\|get_attrs_list_offset -\|----\ \|
	\| \| \| \|
	\|retrieved_attrs_alloc_len\| \| \|
	\|retrieved_attrs_offset -\|----\|----\|-\
	\| \| \| \| \|
	\|set_attrs_list_length \| \| \| \|
	\|set_attrs_list_offset -\|-\ \| \| \|
	\| \| \| \| \| \|
	\|in_data_integ_offset -\|-\|--\|----\|-\|-\
	\|out_data_integ_offset -\|-\|--\|--\ \| \| \|
	\_________________________/ \| \| \| \| \| \|
	\| \| \| \| \| \|
	\|_______OUT-BUFFER________\| \| \| \| \| \| \|
	\| Set attr list \|</ \| \| \| \| \|
	\| \| \| \| \| \| \|
	\|-------------------------\| \| \| \| \| \|
	\| Get attr descriptors \|<---/ \| \| \| \|
	\| \| \| \| \| \|
	\|-------------------------\| \| \| \| \|
	\| Out-data integrity \|<------/ \| \| \|
	\| \| \| \| \|
	\_________________________/ \| \| \|
	\| \| \|
	\|________IN-BUFFER________\| \| \| \|
	\| In-Data read \|<--------/ \| \|
	\| \| \| \|
	\|-------------------------\| \| \|
	\| Get attr list \|<----------/ \|
	\| \| \|
	\|-------------------------\| \|
	\| In-data integrity \|<------------/
	\| \|
	\_________________________/

	A block device request can carry bidirectional payload by means of associating
	a bidi_read request with a main write-request. Each in/out request is described
	by a chain of BIOs associated with each request.
	The CDB is of a SCSI VARLEN CDB format, as described by OSD standard.
	The OSD standard also mandates alignment restrictions at start of each segment.

	In the code, in struct osd_request, there are two _osd_io_info structures to
	describe the IN/OUT buffers above, two BIOs for the data payload and up to five
	_osd_req_data_segment structures to hold the different segments allocation and
	information.

	Important: We have chosen to disregard the assumption that a BIO-chain (and
	the resulting sg-list) describes a linear memory buffer. Meaning only first and
	last scatter chain can be incomplete and all the middle chains are of PAGE_SIZE.
	For us, a scatter-gather-list, as its name implies and as used by the Networking
	layer, is to describe a vector of buffers that will be transferred to/from the
	wire. It works very well with current iSCSI transport. iSCSI is currently the
	only deployed OSD transport. In the future we anticipate SAS and FC attached OSD
	devices as well.

	The OSD Testing ULD
	===================
	TODO: More user-mode control on tests.

	Authors, Mailing list
	=====================
	Please communicate with us on any deployment of osd, whether using this code
	or not.

	Any problems, questions, bug reports, lonely OSD nights, please email:
	OSD Dev List <osd-dev@open-osd.org>

	More up-to-date information can be found on:
	http://open-osd.org

	Boaz Harrosh <bharrosh@panasas.com>
	Benny Halevy <bhalevy@panasas.com>

	References
	==========
	Weber, R., "SCSI Object-Based Storage Device Commands",
	T10/1355-D ANSI/INCITS 400-2004,
	http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf

	Weber, R., "SCSI Object-Based Storage Device Commands -2 (OSD-2)"
	T10/1729-D, Working Draft, rev. 3
	http://www.t10.org/ftp/t10/drafts/osd2/osd2r03.pdf