Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 The OSD Standard 2 ================ 3 OSD (Object-Based Storage Device) is a T10 SCSI command set that is designed 4 to provide efficient operation of input/output logical units that manage the 5 allocation, placement, and accessing of variable-size data-storage containers, 6 called objects. Objects are intended to contain operating system and application 7 constructs. Each object has associated attributes attached to it, which are 8 integral part of the object and provide metadata about the object. The standard 9 defines some common obligatory attributes, but user attributes can be added as 10 needed. 11 12 See: http://www.t10.org/ftp/t10/drafts/osd2/ for the latest draft for OSD 2 13 or search the web for "OSD SCSI" 14 15 OSD in the Linux Kernel 16 ======================= 17 osd-initiator: 18 The main component of OSD in Kernel is the osd-initiator library. Its main 19 user is intended to be the pNFS-over-objects layout driver, which uses objects 20 as its back-end data storage. Other clients are the other osd parts listed below. 21 22 osd-uld: 23 This is a SCSI ULD that registers for OSD type devices and provides a testing 24 platform, both for the in-kernel initiator as well as connected targets. It 25 currently has no useful user-mode API, though it could have if need be. 26 27 exofs: 28 Is an OSD based Linux file system. It uses the osd-initiator and osd-uld, 29 to export a usable file system for users. 30 See Documentation/filesystems/exofs.txt for more details 31 32 osd target: 33 There are no current plans for an OSD target implementation in kernel. For all 34 needs, a user-mode target that is based on the scsi tgt target framework is 35 available from Ohio Supercomputer Center (OSC) at: 36 http://www.open-osd.org/bin/view/Main/OscOsdProject 37 There are several other target implementations. See http://open-osd.org for more 38 links. 39 40 Files and Folders 41 ================= 42 This is the complete list of files included in this work: 43 include/scsi/ 44 osd_initiator.h Main API for the initiator library 45 osd_types.h Common OSD types 46 osd_sec.h Security Manager API 47 osd_protocol.h Wire definitions of the OSD standard protocol 48 osd_attributes.h Wire definitions of OSD attributes 49 50 drivers/scsi/osd/ 51 osd_initiator.c OSD-Initiator library implementation 52 osd_uld.c The OSD scsi ULD 53 osd_ktest.{h,c} In-kernel test suite (called by osd_uld) 54 osd_debug.h Some printk macros 55 Makefile For both in-tree and out-of-tree compilation 56 Kconfig Enables inclusion of the different pieces 57 osd_test.c User-mode application to call the kernel tests 58 59 The OSD-Initiator Library 60 ========================= 61 osd_initiator is a low level implementation of an osd initiator encoder. 62 But even though, it should be intuitive and easy to use. Perhaps over time an 63 higher lever will form that automates some of the more common recipes. 64 65 init/fini: 66 - osd_dev_init() associates a scsi_device with an osd_dev structure 67 and initializes some global pools. This should be done once per scsi_device 68 (OSD LUN). The osd_dev structure is needed for calling osd_start_request(). 69 70 - osd_dev_fini() cleans up before a osd_dev/scsi_device destruction. 71 72 OSD commands encoding, execution, and decoding of results: 73 74 struct osd_request's is used to iteratively encode an OSD command and carry 75 its state throughout execution. Each request goes through these stages: 76 77 a. osd_start_request() allocates the request. 78 79 b. Any of the osd_req_* methods is used to encode a request of the specified 80 type. 81 82 c. osd_req_add_{get,set}_attr_* may be called to add get/set attributes to the 83 CDB. "List" or "Page" mode can be used exclusively. The attribute-list API 84 can be called multiple times on the same request. However, only one 85 attribute-page can be read, as mandated by the OSD standard. 86 87 d. osd_finalize_request() computes offsets into the data-in and data-out buffers 88 and signs the request using the provided capability key and integrity- 89 check parameters. 90 91 e. osd_execute_request() may be called to execute the request via the block 92 layer and wait for its completion. The request can be executed 93 asynchronously by calling the block layer API directly. 94 95 f. After execution, osd_req_decode_sense() can be called to decode the request's 96 sense information. 97 98 g. osd_req_decode_get_attr() may be called to retrieve osd_add_get_attr_list() 99 values. 100 101 h. osd_end_request() must be called to deallocate the request and any resource 102 associated with it. Note that osd_end_request cleans up the request at any 103 stage and it must always be called after a successful osd_start_request(). 104 105 osd_request's structure: 106 107 The OSD standard defines a complex structure of IO segments pointed to by 108 members in the CDB. Up to 3 segments can be deployed in the IN-Buffer and up to 109 4 in the OUT-Buffer. The ASCII illustration below depicts a secure-read with 110 associated get+set of attributes-lists. Other combinations very on the same 111 basic theme. From no-segments-used up to all-segments-used. 112 113 |________OSD-CDB__________| 114 | | 115 |read_len (offset=0) -|---------\ 116 | | | 117 |get_attrs_list_length | | 118 |get_attrs_list_offset -|----\ | 119 | | | | 120 |retrieved_attrs_alloc_len| | | 121 |retrieved_attrs_offset -|----|----|-\ 122 | | | | | 123 |set_attrs_list_length | | | | 124 |set_attrs_list_offset -|-\ | | | 125 | | | | | | 126 |in_data_integ_offset -|-|--|----|-|-\ 127 |out_data_integ_offset -|-|--|--\ | | | 128 \_________________________/ | | | | | | 129 | | | | | | 130 |_______OUT-BUFFER________| | | | | | | 131 | Set attr list |</ | | | | | 132 | | | | | | | 133 |-------------------------| | | | | | 134 | Get attr descriptors |<---/ | | | | 135 | | | | | | 136 |-------------------------| | | | | 137 | Out-data integrity |<------/ | | | 138 | | | | | 139 \_________________________/ | | | 140 | | | 141 |________IN-BUFFER________| | | | 142 | In-Data read |<--------/ | | 143 | | | | 144 |-------------------------| | | 145 | Get attr list |<----------/ | 146 | | | 147 |-------------------------| | 148 | In-data integrity |<------------/ 149 | | 150 \_________________________/ 151 152 A block device request can carry bidirectional payload by means of associating 153 a bidi_read request with a main write-request. Each in/out request is described 154 by a chain of BIOs associated with each request. 155 The CDB is of a SCSI VARLEN CDB format, as described by OSD standard. 156 The OSD standard also mandates alignment restrictions at start of each segment. 157 158 In the code, in struct osd_request, there are two _osd_io_info structures to 159 describe the IN/OUT buffers above, two BIOs for the data payload and up to five 160 _osd_req_data_segment structures to hold the different segments allocation and 161 information. 162 163 Important: We have chosen to disregard the assumption that a BIO-chain (and 164 the resulting sg-list) describes a linear memory buffer. Meaning only first and 165 last scatter chain can be incomplete and all the middle chains are of PAGE_SIZE. 166 For us, a scatter-gather-list, as its name implies and as used by the Networking 167 layer, is to describe a vector of buffers that will be transferred to/from the 168 wire. It works very well with current iSCSI transport. iSCSI is currently the 169 only deployed OSD transport. In the future we anticipate SAS and FC attached OSD 170 devices as well. 171 172 The OSD Testing ULD 173 =================== 174 TODO: More user-mode control on tests. 175 176 Authors, Mailing list 177 ===================== 178 Please communicate with us on any deployment of osd, whether using this code 179 or not. 180 181 Any problems, questions, bug reports, lonely OSD nights, please email: 182 OSD Dev List <osd-dev@open-osd.org> 183 184 More up-to-date information can be found on: 185 http://open-osd.org 186 187 Boaz Harrosh <ooo@electrozaur.com> 188 189 References 190 ========== 191 Weber, R., "SCSI Object-Based Storage Device Commands", 192 T10/1355-D ANSI/INCITS 400-2004, 193 http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf 194 195 Weber, R., "SCSI Object-Based Storage Device Commands -2 (OSD-2)" 196 T10/1729-D, Working Draft, rev. 3 197 http://www.t10.org/ftp/t10/drafts/osd2/osd2r03.pdf