include/hw/xen/interface/io/blkif.h

   1 /* SPDX-License-Identifier: MIT */
   2 /******************************************************************************
   3  * blkif.h
   4  *
   5  * Unified block-device I/O interface for Xen guest OSes.
   6  *
   7  * Copyright (c) 2003-2004, Keir Fraser
   8  * Copyright (c) 2012, Spectra Logic Corporation
   9  */
  10
  11 #ifndef __XEN_PUBLIC_IO_BLKIF_H__
  12 #define __XEN_PUBLIC_IO_BLKIF_H__
  13
  14 #include "ring.h"
  15 #include "../grant_table.h"
  16
  17 /*
  18  * Front->back notifications: When enqueuing a new request, sending a
  19  * notification can be made conditional on req_event (i.e., the generic
  20  * hold-off mechanism provided by the ring macros). Backends must set
  21  * req_event appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
  22  *
  23  * Back->front notifications: When enqueuing a new response, sending a
  24  * notification can be made conditional on rsp_event (i.e., the generic
  25  * hold-off mechanism provided by the ring macros). Frontends must set
  26  * rsp_event appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
  27  */
  28
  29 #ifndef blkif_vdev_t
  30 #define blkif_vdev_t   uint16_t
  31 #endif
  32 #define blkif_sector_t uint64_t
  33
  34 /*
  35  * Feature and Parameter Negotiation
  36  * =================================
  37  * The two halves of a Xen block driver utilize nodes within the XenStore to
  38  * communicate capabilities and to negotiate operating parameters.  This
  39  * section enumerates these nodes which reside in the respective front and
  40  * backend portions of the XenStore, following the XenBus convention.
  41  *
  42  * All data in the XenStore is stored as strings.  Nodes specifying numeric
  43  * values are encoded in decimal.  Integer value ranges listed below are
  44  * expressed as fixed sized integer types capable of storing the conversion
  45  * of a properly formated node string, without loss of information.
  46  *
  47  * Any specified default value is in effect if the corresponding XenBus node
  48  * is not present in the XenStore.
  49  *
  50  * XenStore nodes in sections marked "PRIVATE" are solely for use by the
  51  * driver side whose XenBus tree contains them.
  52  *
  53  * XenStore nodes marked "DEPRECATED" in their notes section should only be
  54  * used to provide interoperability with legacy implementations.
  55  *
  56  * See the XenBus state transition diagram below for details on when XenBus
  57  * nodes must be published and when they can be queried.
  58  *
  59  *****************************************************************************
  60  *                            Backend XenBus Nodes
  61  *****************************************************************************
  62  *
  63  *------------------ Backend Device Identification (PRIVATE) ------------------
  64  *
  65  * mode
  66  *      Values:         "r" (read only), "w" (writable)
  67  *
  68  *      The read or write access permissions to the backing store to be
  69  *      granted to the frontend.
  70  *
  71  * params
  72  *      Values:         string
  73  *
  74  *      A free formatted string providing sufficient information for the
  75  *      hotplug script to attach the device and provide a suitable
  76  *      handler (ie: a block device) for blkback to use.
  77  *
  78  * physical-device
  79  *      Values:         "MAJOR:MINOR"
  80  *      Notes: 11
  81  *
  82  *      MAJOR and MINOR are the major number and minor number of the
  83  *      backing device respectively.
  84  *
  85  * physical-device-path
  86  *      Values:         path string
  87  *
  88  *      A string that contains the absolute path to the disk image. On
  89  *      NetBSD and Linux this is always a block device, while on FreeBSD
  90  *      it can be either a block device or a regular file.
  91  *
  92  * type
  93  *      Values:         "file", "phy", "tap"
  94  *
  95  *      The type of the backing device/object.
  96  *
  97  *
  98  * direct-io-safe
  99  *      Values:         0/1 (boolean)
 100  *      Default Value:  0
 101  *
 102  *      The underlying storage is not affected by the direct IO memory
 103  *      lifetime bug.  See:
 104  *        https://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
 105  *
 106  *      Therefore this option gives the backend permission to use
 107  *      O_DIRECT, notwithstanding that bug.
 108  *
 109  *      That is, if this option is enabled, use of O_DIRECT is safe,
 110  *      in circumstances where we would normally have avoided it as a
 111  *      workaround for that bug.  This option is not relevant for all
 112  *      backends, and even not necessarily supported for those for
 113  *      which it is relevant.  A backend which knows that it is not
 114  *      affected by the bug can ignore this option.
 115  *
 116  *      This option doesn't require a backend to use O_DIRECT, so it
 117  *      should not be used to try to control the caching behaviour.
 118  *
 119  *--------------------------------- Features ---------------------------------
 120  *
 121  * feature-barrier
 122  *      Values:         0/1 (boolean)
 123  *      Default Value:  0
 124  *
 125  *      A value of "1" indicates that the backend can process requests
 126  *      containing the BLKIF_OP_WRITE_BARRIER request opcode.  Requests
 127  *      of this type may still be returned at any time with the
 128  *      BLKIF_RSP_EOPNOTSUPP result code.
 129  *
 130  * feature-flush-cache
 131  *      Values:         0/1 (boolean)
 132  *      Default Value:  0
 133  *
 134  *      A value of "1" indicates that the backend can process requests
 135  *      containing the BLKIF_OP_FLUSH_DISKCACHE request opcode.  Requests
 136  *      of this type may still be returned at any time with the
 137  *      BLKIF_RSP_EOPNOTSUPP result code.
 138  *
 139  * feature-discard
 140  *      Values:         0/1 (boolean)
 141  *      Default Value:  0
 142  *
 143  *      A value of "1" indicates that the backend can process requests
 144  *      containing the BLKIF_OP_DISCARD request opcode.  Requests
 145  *      of this type may still be returned at any time with the
 146  *      BLKIF_RSP_EOPNOTSUPP result code.
 147  *
 148  * feature-persistent
 149  *      Values:         0/1 (boolean)
 150  *      Default Value:  0
 151  *      Notes: 7
 152  *
 153  *      A value of "1" indicates that the backend can keep the grants used
 154  *      by the frontend driver mapped, so the same set of grants should be
 155  *      used in all transactions. The maximum number of grants the backend
 156  *      can map persistently depends on the implementation, but ideally it
 157  *      should be RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST. Using this
 158  *      feature the backend doesn't need to unmap each grant, preventing
 159  *      costly TLB flushes. The backend driver should only map grants
 160  *      persistently if the frontend supports it. If a backend driver chooses
 161  *      to use the persistent protocol when the frontend doesn't support it,
 162  *      it will probably hit the maximum number of persistently mapped grants
 163  *      (due to the fact that the frontend won't be reusing the same grants),
 164  *      and fall back to non-persistent mode. Backend implementations may
 165  *      shrink or expand the number of persistently mapped grants without
 166  *      notifying the frontend depending on memory constraints (this might
 167  *      cause a performance degradation).
 168  *
 169  *      If a backend driver wants to limit the maximum number of persistently
 170  *      mapped grants to a value less than RING_SIZE *
 171  *      BLKIF_MAX_SEGMENTS_PER_REQUEST a LRU strategy should be used to
 172  *      discard the grants that are less commonly used. Using a LRU in the
 173  *      backend driver paired with a LIFO queue in the frontend will
 174  *      allow us to have better performance in this scenario.
 175  *
 176  *----------------------- Request Transport Parameters ------------------------
 177  *
 178  * max-ring-page-order
 179  *      Values:         <uint32_t>
 180  *      Default Value:  0
 181  *      Notes:          1, 3
 182  *
 183  *      The maximum supported size of the request ring buffer in units of
 184  *      lb(machine pages). (e.g. 0 == 1 page,  1 = 2 pages, 2 == 4 pages,
 185  *      etc.).
 186  *
 187  * max-ring-pages
 188  *      Values:         <uint32_t>
 189  *      Default Value:  1
 190  *      Notes:          DEPRECATED, 2, 3
 191  *
 192  *      The maximum supported size of the request ring buffer in units of
 193  *      machine pages.  The value must be a power of 2.
 194  *
 195  *------------------------- Backend Device Properties -------------------------
 196  *
 197  * discard-enable
 198  *      Values:         0/1 (boolean)
 199  *      Default Value:  1
 200  *
 201  *      This optional property, set by the toolstack, instructs the backend
 202  *      to offer (or not to offer) discard to the frontend. If the property
 203  *      is missing the backend should offer discard if the backing storage
 204  *      actually supports it.
 205  *
 206  * discard-alignment
 207  *      Values:         <uint32_t>
 208  *      Default Value:  0
 209  *      Notes:          4, 5
 210  *
 211  *      The offset, in bytes from the beginning of the virtual block device,
 212  *      to the first, addressable, discard extent on the underlying device.
 213  *
 214  * discard-granularity
 215  *      Values:         <uint32_t>
 216  *      Default Value:  <"sector-size">
 217  *      Notes:          4
 218  *
 219  *      The size, in bytes, of the individually addressable discard extents
 220  *      of the underlying device.
 221  *
 222  * discard-secure
 223  *      Values:         0/1 (boolean)
 224  *      Default Value:  0
 225  *      Notes:          10
 226  *
 227  *      A value of "1" indicates that the backend can process BLKIF_OP_DISCARD
 228  *      requests with the BLKIF_DISCARD_SECURE flag set.
 229  *
 230  * info
 231  *      Values:         <uint32_t> (bitmap)
 232  *
 233  *      A collection of bit flags describing attributes of the backing
 234  *      device.  The VDISK_* macros define the meaning of each bit
 235  *      location.
 236  *
 237  * sector-size
 238  *      Values:         <uint32_t>
 239  *
 240  *      The logical block size, in bytes, of the underlying storage. This
 241  *      must be a power of two with a minimum value of 512.
 242  *
 243  *      NOTE: Because of implementation bugs in some frontends this must be
 244  *            set to 512, unless the frontend advertizes a non-zero value
 245  *            in its "feature-large-sector-size" xenbus node. (See below).
 246  *
 247  * physical-sector-size
 248  *      Values:         <uint32_t>
 249  *      Default Value:  <"sector-size">
 250  *
 251  *      The physical block size, in bytes, of the backend storage. This
 252  *      must be an integer multiple of "sector-size".
 253  *
 254  * sectors
 255  *      Values:         <uint64_t>
 256  *
 257  *      The size of the backend device, expressed in units of "sector-size".
 258  *      The product of "sector-size" and "sectors" must also be an integer
 259  *      multiple of "physical-sector-size", if that node is present.
 260  *
 261  *****************************************************************************
 262  *                            Frontend XenBus Nodes
 263  *****************************************************************************
 264  *
 265  *----------------------- Request Transport Parameters -----------------------
 266  *
 267  * event-channel
 268  *      Values:         <uint32_t>
 269  *
 270  *      The identifier of the Xen event channel used to signal activity
 271  *      in the ring buffer.
 272  *
 273  * ring-ref
 274  *      Values:         <uint32_t>
 275  *      Notes:          6
 276  *
 277  *      The Xen grant reference granting permission for the backend to map
 278  *      the sole page in a single page sized ring buffer.
 279  *
 280  * ring-ref%u
 281  *      Values:         <uint32_t>
 282  *      Notes:          6
 283  *
 284  *      For a frontend providing a multi-page ring, a "number of ring pages"
 285  *      sized list of nodes, each containing a Xen grant reference granting
 286  *      permission for the backend to map the page of the ring located
 287  *      at page index "%u".  Page indexes are zero based.
 288  *
 289  * protocol
 290  *      Values:         string (XEN_IO_PROTO_ABI_*)
 291  *      Default Value:  XEN_IO_PROTO_ABI_NATIVE
 292  *
 293  *      The machine ABI rules governing the format of all ring request and
 294  *      response structures.
 295  *
 296  * ring-page-order
 297  *      Values:         <uint32_t>
 298  *      Default Value:  0
 299  *      Maximum Value:  MAX(ffs(max-ring-pages) - 1, max-ring-page-order)
 300  *      Notes:          1, 3
 301  *
 302  *      The size of the frontend allocated request ring buffer in units
 303  *      of lb(machine pages). (e.g. 0 == 1 page, 1 = 2 pages, 2 == 4 pages,
 304  *      etc.).
 305  *
 306  * num-ring-pages
 307  *      Values:         <uint32_t>
 308  *      Default Value:  1
 309  *      Maximum Value:  MAX(max-ring-pages,(0x1 << max-ring-page-order))
 310  *      Notes:          DEPRECATED, 2, 3
 311  *
 312  *      The size of the frontend allocated request ring buffer in units of
 313  *      machine pages.  The value must be a power of 2.
 314  *
 315  *--------------------------------- Features ---------------------------------
 316  *
 317  * feature-persistent
 318  *      Values:         0/1 (boolean)
 319  *      Default Value:  0
 320  *      Notes: 7, 8, 9
 321  *
 322  *      A value of "1" indicates that the frontend will reuse the same grants
 323  *      for all transactions, allowing the backend to map them with write
 324  *      access (even when it should be read-only). If the frontend hits the
 325  *      maximum number of allowed persistently mapped grants, it can fallback
 326  *      to non persistent mode. This will cause a performance degradation,
 327  *      since the the backend driver will still try to map those grants
 328  *      persistently. Since the persistent grants protocol is compatible with
 329  *      the previous protocol, a frontend driver can choose to work in
 330  *      persistent mode even when the backend doesn't support it.
 331  *
 332  *      It is recommended that the frontend driver stores the persistently
 333  *      mapped grants in a LIFO queue, so a subset of all persistently mapped
 334  *      grants gets used commonly. This is done in case the backend driver
 335  *      decides to limit the maximum number of persistently mapped grants
 336  *      to a value less than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST.
 337  *
 338  * feature-large-sector-size
 339  *      Values:         0/1 (boolean)
 340  *      Default Value:  0
 341  *
 342  *      A value of "1" indicates that the frontend will correctly supply and
 343  *      interpret all sector-based quantities in terms of the "sector-size"
 344  *      value supplied in the backend info, whatever that may be set to.
 345  *      If this node is not present or its value is "0" then it is assumed
 346  *      that the frontend requires that the logical block size is 512 as it
 347  *      is hardcoded (which is the case in some frontend implementations).
 348  *
 349  * trusted
 350  *      Values:         0/1 (boolean)
 351  *      Default value:  1
 352  *
 353  *      A value of "0" indicates that the frontend should not trust the
 354  *      backend, and should deploy whatever measures available to protect from
 355  *      a malicious backend on the other end.
 356  *
 357  *------------------------- Virtual Device Properties -------------------------
 358  *
 359  * device-type
 360  *      Values:         "disk", "cdrom", "floppy", etc.
 361  *
 362  * virtual-device
 363  *      Values:         <uint32_t>
 364  *
 365  *      A value indicating the physical device to virtualize within the
 366  *      frontend's domain.  (e.g. "The first ATA disk", "The third SCSI
 367  *      disk", etc.)
 368  *
 369  *      See docs/misc/vbd-interface.txt for details on the format of this
 370  *      value.
 371  *
 372  * Notes
 373  * -----
 374  * (1) Multi-page ring buffer scheme first developed in the Citrix XenServer
 375  *     PV drivers.
 376  * (2) Multi-page ring buffer scheme first used in some RedHat distributions
 377  *     including a distribution deployed on certain nodes of the Amazon
 378  *     EC2 cluster.
 379  * (3) Support for multi-page ring buffers was implemented independently,
 380  *     in slightly different forms, by both Citrix and RedHat/Amazon.
 381  *     For full interoperability, block front and backends should publish
 382  *     identical ring parameters, adjusted for unit differences, to the
 383  *     XenStore nodes used in both schemes.
 384  * (4) Devices that support discard functionality may internally allocate space
 385  *     (discardable extents) in units that are larger than the exported logical
 386  *     block size. If the backing device has such discardable extents the
 387  *     backend should provide both discard-granularity and discard-alignment.
 388  *     Providing just one of the two may be considered an error by the frontend.
 389  *     Backends supporting discard should include discard-granularity and
 390  *     discard-alignment even if it supports discarding individual sectors.
 391  *     Frontends should assume discard-alignment == 0 and discard-granularity
 392  *     == sector size if these keys are missing.
 393  * (5) The discard-alignment parameter allows a physical device to be
 394  *     partitioned into virtual devices that do not necessarily begin or
 395  *     end on a discardable extent boundary.
 396  * (6) When there is only a single page allocated to the request ring,
 397  *     'ring-ref' is used to communicate the grant reference for this
 398  *     page to the backend.  When using a multi-page ring, the 'ring-ref'
 399  *     node is not created.  Instead 'ring-ref0' - 'ring-refN' are used.
 400  * (7) When using persistent grants data has to be copied from/to the page
 401  *     where the grant is currently mapped. The overhead of doing this copy
 402  *     however doesn't suppress the speed improvement of not having to unmap
 403  *     the grants.
 404  * (8) The frontend driver has to allow the backend driver to map all grants
 405  *     with write access, even when they should be mapped read-only, since
 406  *     further requests may reuse these grants and require write permissions.
 407  * (9) Linux implementation doesn't have a limit on the maximum number of
 408  *     grants that can be persistently mapped in the frontend driver, but
 409  *     due to the frontent driver implementation it should never be bigger
 410  *     than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST.
 411  *(10) The discard-secure property may be present and will be set to 1 if the
 412  *     backing device supports secure discard.
 413  *(11) Only used by Linux and NetBSD.
 414  */
 415
 416 /*
 417  * Multiple hardware queues/rings:
 418  * If supported, the backend will write the key "multi-queue-max-queues" to
 419  * the directory for that vbd, and set its value to the maximum supported
 420  * number of queues.
 421  * Frontends that are aware of this feature and wish to use it can write the
 422  * key "multi-queue-num-queues" with the number they wish to use, which must be
 423  * greater than zero, and no more than the value reported by the backend in
 424  * "multi-queue-max-queues".
 425  *
 426  * For frontends requesting just one queue, the usual event-channel and
 427  * ring-ref keys are written as before, simplifying the backend processing
 428  * to avoid distinguishing between a frontend that doesn't understand the
 429  * multi-queue feature, and one that does, but requested only one queue.
 430  *
 431  * Frontends requesting two or more queues must not write the toplevel
 432  * event-channel and ring-ref keys, instead writing those keys under sub-keys
 433  * having the name "queue-N" where N is the integer ID of the queue/ring for
 434  * which those keys belong. Queues are indexed from zero.
 435  * For example, a frontend with two queues must write the following set of
 436  * queue-related keys:
 437  *
 438  * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"
 439  * /local/domain/1/device/vbd/0/queue-0 = ""
 440  * /local/domain/1/device/vbd/0/queue-0/ring-ref = "<ring-ref#0>"
 441  * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"
 442  * /local/domain/1/device/vbd/0/queue-1 = ""
 443  * /local/domain/1/device/vbd/0/queue-1/ring-ref = "<ring-ref#1>"
 444  * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"
 445  *
 446  * It is also possible to use multiple queues/rings together with
 447  * feature multi-page ring buffer.
 448  * For example, a frontend requests two queues/rings and the size of each ring
 449  * buffer is two pages must write the following set of related keys:
 450  *
 451  * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"
 452  * /local/domain/1/device/vbd/0/ring-page-order = "1"
 453  * /local/domain/1/device/vbd/0/queue-0 = ""
 454  * /local/domain/1/device/vbd/0/queue-0/ring-ref0 = "<ring-ref#0>"
 455  * /local/domain/1/device/vbd/0/queue-0/ring-ref1 = "<ring-ref#1>"
 456  * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"
 457  * /local/domain/1/device/vbd/0/queue-1 = ""
 458  * /local/domain/1/device/vbd/0/queue-1/ring-ref0 = "<ring-ref#2>"
 459  * /local/domain/1/device/vbd/0/queue-1/ring-ref1 = "<ring-ref#3>"
 460  * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"
 461  *
 462  */
 463
 464 /*
 465  * STATE DIAGRAMS
 466  *
 467  *****************************************************************************
 468  *                                   Startup                                 *
 469  *****************************************************************************
 470  *
 471  * Tool stack creates front and back nodes with state XenbusStateInitialising.
 472  *
 473  * Front                                Back
 474  * =================================    =====================================
 475  * XenbusStateInitialising              XenbusStateInitialising
 476  *  o Query virtual device               o Query backend device identification
 477  *    properties.                          data.
 478  *  o Setup OS device instance.          o Open and validate backend device.
 479  *                                       o Publish backend features and
 480  *                                         transport parameters.
 481  *                                                      |
 482  *                                                      |
 483  *                                                      V
 484  *                                      XenbusStateInitWait
 485  *
 486  * o Query backend features and
 487  *   transport parameters.
 488  * o Allocate and initialize the
 489  *   request ring.
 490  * o Publish transport parameters
 491  *   that will be in effect during
 492  *   this connection.
 493  *              |
 494  *              |
 495  *              V
 496  * XenbusStateInitialised
 497  *
 498  *                                       o Query frontend transport parameters.
 499  *                                       o Connect to the request ring and
 500  *                                         event channel.
 501  *                                       o Publish backend device properties.
 502  *                                                      |
 503  *                                                      |
 504  *                                                      V
 505  *                                      XenbusStateConnected
 506  *
 507  *  o Query backend device properties.
 508  *  o Finalize OS virtual device
 509  *    instance.
 510  *              |
 511  *              |
 512  *              V
 513  * XenbusStateConnected
 514  *
 515  * Note: Drivers that do not support any optional features, or the negotiation
 516  *       of transport parameters, can skip certain states in the state machine:
 517  *
 518  *       o A frontend may transition to XenbusStateInitialised without
 519  *         waiting for the backend to enter XenbusStateInitWait.  In this
 520  *         case, default transport parameters are in effect and any
 521  *         transport parameters published by the frontend must contain
 522  *         their default values.
 523  *
 524  *       o A backend may transition to XenbusStateInitialised, bypassing
 525  *         XenbusStateInitWait, without waiting for the frontend to first
 526  *         enter the XenbusStateInitialised state.  In this case, default
 527  *         transport parameters are in effect and any transport parameters
 528  *         published by the backend must contain their default values.
 529  *
 530  *       Drivers that support optional features and/or transport parameter
 531  *       negotiation must tolerate these additional state transition paths.
 532  *       In general this means performing the work of any skipped state
 533  *       transition, if it has not already been performed, in addition to the
 534  *       work associated with entry into the current state.
 535  */
 536
 537 /*
 538  * REQUEST CODES.
 539  */
 540 #define BLKIF_OP_READ              0
 541 #define BLKIF_OP_WRITE             1
 542 /*
 543  * All writes issued prior to a request with the BLKIF_OP_WRITE_BARRIER
 544  * operation code ("barrier request") must be completed prior to the
 545  * execution of the barrier request.  All writes issued after the barrier
 546  * request must not execute until after the completion of the barrier request.
 547  *
 548  * Optional.  See "feature-barrier" XenBus node documentation above.
 549  */
 550 #define BLKIF_OP_WRITE_BARRIER     2
 551 /*
 552  * Commit any uncommitted contents of the backing device's volatile cache
 553  * to stable storage.
 554  *
 555  * Optional.  See "feature-flush-cache" XenBus node documentation above.
 556  */
 557 #define BLKIF_OP_FLUSH_DISKCACHE   3
 558 /*
 559  * Used in SLES sources for device specific command packet
 560  * contained within the request. Reserved for that purpose.
 561  */
 562 #define BLKIF_OP_RESERVED_1        4
 563 /*
 564  * Indicate to the backend device that a region of storage is no longer in
 565  * use, and may be discarded at any time without impact to the client.  If
 566  * the BLKIF_DISCARD_SECURE flag is set on the request, all copies of the
 567  * discarded region on the device must be rendered unrecoverable before the
 568  * command returns.
 569  *
 570  * This operation is analogous to performing a trim (ATA) or unamp (SCSI),
 571  * command on a native device.
 572  *
 573  * More information about trim/unmap operations can be found at:
 574  * http://t13.org/Documents/UploadedDocuments/docs2008/
 575  *     e07154r6-Data_Set_Management_Proposal_for_ATA-ACS2.doc
 576  * http://www.seagate.com/staticfiles/support/disc/manuals/
 577  *     Interface%20manuals/100293068c.pdf
 578  *
 579  * Optional.  See "feature-discard", "discard-alignment",
 580  * "discard-granularity", and "discard-secure" in the XenBus node
 581  * documentation above.
 582  */
 583 #define BLKIF_OP_DISCARD           5
 584
 585 /*
 586  * Recognized if "feature-max-indirect-segments" in present in the backend
 587  * xenbus info. The "feature-max-indirect-segments" node contains the maximum
 588  * number of segments allowed by the backend per request. If the node is
 589  * present, the frontend might use blkif_request_indirect structs in order to
 590  * issue requests with more than BLKIF_MAX_SEGMENTS_PER_REQUEST (11). The
 591  * maximum number of indirect segments is fixed by the backend, but the
 592  * frontend can issue requests with any number of indirect segments as long as
 593  * it's less than the number provided by the backend. The indirect_grefs field
 594  * in blkif_request_indirect should be filled by the frontend with the
 595  * grant references of the pages that are holding the indirect segments.
 596  * These pages are filled with an array of blkif_request_segment that hold the
 597  * information about the segments. The number of indirect pages to use is
 598  * determined by the number of segments an indirect request contains. Every
 599  * indirect page can contain a maximum of
 600  * (PAGE_SIZE / sizeof(struct blkif_request_segment)) segments, so to
 601  * calculate the number of indirect pages to use we have to do
 602  * ceil(indirect_segments / (PAGE_SIZE / sizeof(struct blkif_request_segment))).
 603  *
 604  * If a backend does not recognize BLKIF_OP_INDIRECT, it should *not*
 605  * create the "feature-max-indirect-segments" node!
 606  */
 607 #define BLKIF_OP_INDIRECT          6
 608
 609 /*
 610  * Maximum scatter/gather segments per request.
 611  * This is carefully chosen so that sizeof(blkif_ring_t) <= PAGE_SIZE.
 612  * NB. This could be 12 if the ring indexes weren't stored in the same page.
 613  */
 614 #define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
 615
 616 /*
 617  * Maximum number of indirect pages to use per request.
 618  */
 619 #define BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST 8
 620
 621 /*
 622  * NB. 'first_sect' and 'last_sect' in blkif_request_segment, as well as
 623  * 'sector_number' in blkif_request, blkif_request_discard and
 624  * blkif_request_indirect are sector-based quantities. See the description
 625  * of the "feature-large-sector-size" frontend xenbus node above for
 626  * more information.
 627  */
 628 struct blkif_request_segment {
 629     grant_ref_t gref;        /* reference to I/O buffer frame        */
 630     /* @first_sect: first sector in frame to transfer (inclusive).   */
 631     /* @last_sect: last sector in frame to transfer (inclusive).     */
 632     uint8_t     first_sect, last_sect;
 633 };
 634
 635 /*
 636  * Starting ring element for any I/O request.
 637  */
 638 struct blkif_request {
 639     uint8_t        operation;    /* BLKIF_OP_???                         */
 640     uint8_t        nr_segments;  /* number of segments                   */
 641     blkif_vdev_t   handle;       /* only for read/write requests         */
 642     uint64_t       id;           /* private guest value, echoed in resp  */
 643     blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 644     struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 645 };
 646 typedef struct blkif_request blkif_request_t;
 647
 648 /*
 649  * Cast to this structure when blkif_request.operation == BLKIF_OP_DISCARD
 650  * sizeof(struct blkif_request_discard) <= sizeof(struct blkif_request)
 651  */
 652 struct blkif_request_discard {
 653     uint8_t        operation;    /* BLKIF_OP_DISCARD                     */
 654     uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
 655 #define BLKIF_DISCARD_SECURE (1<<0)  /* ignored if discard-secure=0      */
 656     blkif_vdev_t   handle;       /* same as for read/write requests      */
 657     uint64_t       id;           /* private guest value, echoed in resp  */
 658     blkif_sector_t sector_number;/* start sector idx on disk             */
 659     uint64_t       nr_sectors;   /* number of contiguous sectors to discard*/
 660 };
 661 typedef struct blkif_request_discard blkif_request_discard_t;
 662
 663 struct blkif_request_indirect {
 664     uint8_t        operation;    /* BLKIF_OP_INDIRECT                    */
 665     uint8_t        indirect_op;  /* BLKIF_OP_{READ/WRITE}                */
 666     uint16_t       nr_segments;  /* number of segments                   */
 667     uint64_t       id;           /* private guest value, echoed in resp  */
 668     blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 669     blkif_vdev_t   handle;       /* same as for read/write requests      */
 670     grant_ref_t    indirect_grefs[BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST];
 671 #ifdef __i386__
 672     uint64_t       pad;          /* Make it 64 byte aligned on i386      */
 673 #endif
 674 };
 675 typedef struct blkif_request_indirect blkif_request_indirect_t;
 676
 677 struct blkif_response {
 678     uint64_t        id;              /* copied from request */
 679     uint8_t         operation;       /* copied from request */
 680     int16_t         status;          /* BLKIF_RSP_???       */
 681 };
 682 typedef struct blkif_response blkif_response_t;
 683
 684 /*
 685  * STATUS RETURN CODES.
 686  */
 687  /* Operation not supported (only happens on barrier writes). */
 688 #define BLKIF_RSP_EOPNOTSUPP  -2
 689  /* Operation failed for some unspecified reason (-EIO). */
 690 #define BLKIF_RSP_ERROR       -1
 691  /* Operation completed successfully. */
 692 #define BLKIF_RSP_OKAY         0
 693
 694 /*
 695  * Generate blkif ring structures and types.
 696  */
 697 DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
 698
 699 #define VDISK_CDROM        0x1
 700 #define VDISK_REMOVABLE    0x2
 701 #define VDISK_READONLY     0x4
 702
 703 #endif /* __XEN_PUBLIC_IO_BLKIF_H__ */
 704
 705 /*
 706  * Local variables:
 707  * mode: C
 708  * c-file-style: "BSD"
 709  * c-basic-offset: 4
 710  * tab-width: 4
 711  * indent-tabs-mode: nil
 712  * End:
 713  */