[SCSI] osd: Documentation for OSD library

Add osd.txt to Documentation/scsi/
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Reviewed-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

Documentation/scsi/osd.txt

+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