xref: /openbmc/qemu/include/hw/xen/interface/io/blkif.h (revision 61f406f3)
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  */
714