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-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