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diff --git a/Documentation/scsi/osd.txt b/Documentation/scsi/osd.txt new file mode 100644 index 000000000..5a9879bad --- /dev/null +++ b/Documentation/scsi/osd.txt @@ -0,0 +1,197 @@ +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 <ooo@electrozaur.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 |