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

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