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+/******************************************************************************
+ * blkif.h
+ *
+ * Unified block-device I/O interface for Xen guest OSes.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Copyright (c) 2003-2004, Keir Fraser
+ * Copyright (c) 2012, Spectra Logic Corporation
+ */
+
+#ifndef __XEN_PUBLIC_IO_BLKIF_H__
+#define __XEN_PUBLIC_IO_BLKIF_H__
+
+#include "ring.h"
+#include "../grant_table.h"
+
+/*
+ * Front->back notifications: When enqueuing a new request, sending a
+ * notification can be made conditional on req_event (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Backends must set
+ * req_event appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
+ *
+ * Back->front notifications: When enqueuing a new response, sending a
+ * notification can be made conditional on rsp_event (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Frontends must set
+ * rsp_event appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
+ */
+
+#ifndef blkif_vdev_t
+#define blkif_vdev_t uint16_t
+#endif
+#define blkif_sector_t uint64_t
+
+/*
+ * Feature and Parameter Negotiation
+ * =================================
+ * The two halves of a Xen block driver utilize nodes within the XenStore to
+ * communicate capabilities and to negotiate operating parameters. This
+ * section enumerates these nodes which reside in the respective front and
+ * backend portions of the XenStore, following the XenBus convention.
+ *
+ * All data in the XenStore is stored as strings. Nodes specifying numeric
+ * values are encoded in decimal. Integer value ranges listed below are
+ * expressed as fixed sized integer types capable of storing the conversion
+ * of a properly formated node string, without loss of information.
+ *
+ * Any specified default value is in effect if the corresponding XenBus node
+ * is not present in the XenStore.
+ *
+ * XenStore nodes in sections marked "PRIVATE" are solely for use by the
+ * driver side whose XenBus tree contains them.
+ *
+ * XenStore nodes marked "DEPRECATED" in their notes section should only be
+ * used to provide interoperability with legacy implementations.
+ *
+ * See the XenBus state transition diagram below for details on when XenBus
+ * nodes must be published and when they can be queried.
+ *
+ *****************************************************************************
+ * Backend XenBus Nodes
+ *****************************************************************************
+ *
+ *------------------ Backend Device Identification (PRIVATE) ------------------
+ *
+ * mode
+ * Values: "r" (read only), "w" (writable)
+ *
+ * The read or write access permissions to the backing store to be
+ * granted to the frontend.
+ *
+ * params
+ * Values: string
+ *
+ * A free formatted string providing sufficient information for the
+ * hotplug script to attach the device and provide a suitable
+ * handler (ie: a block device) for blkback to use.
+ *
+ * physical-device
+ * Values: "MAJOR:MINOR"
+ * Notes: 11
+ *
+ * MAJOR and MINOR are the major number and minor number of the
+ * backing device respectively.
+ *
+ * physical-device-path
+ * Values: path string
+ *
+ * A string that contains the absolute path to the disk image. On
+ * NetBSD and Linux this is always a block device, while on FreeBSD
+ * it can be either a block device or a regular file.
+ *
+ * type
+ * Values: "file", "phy", "tap"
+ *
+ * The type of the backing device/object.
+ *
+ *
+ * direct-io-safe
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ *
+ * The underlying storage is not affected by the direct IO memory
+ * lifetime bug. See:
+ * http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
+ *
+ * Therefore this option gives the backend permission to use
+ * O_DIRECT, notwithstanding that bug.
+ *
+ * That is, if this option is enabled, use of O_DIRECT is safe,
+ * in circumstances where we would normally have avoided it as a
+ * workaround for that bug. This option is not relevant for all
+ * backends, and even not necessarily supported for those for
+ * which it is relevant. A backend which knows that it is not
+ * affected by the bug can ignore this option.
+ *
+ * This option doesn't require a backend to use O_DIRECT, so it
+ * should not be used to try to control the caching behaviour.
+ *
+ *--------------------------------- Features ---------------------------------
+ *
+ * feature-barrier
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ *
+ * A value of "1" indicates that the backend can process requests
+ * containing the BLKIF_OP_WRITE_BARRIER request opcode. Requests
+ * of this type may still be returned at any time with the
+ * BLKIF_RSP_EOPNOTSUPP result code.
+ *
+ * feature-flush-cache
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ *
+ * A value of "1" indicates that the backend can process requests
+ * containing the BLKIF_OP_FLUSH_DISKCACHE request opcode. Requests
+ * of this type may still be returned at any time with the
+ * BLKIF_RSP_EOPNOTSUPP result code.
+ *
+ * feature-discard
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ *
+ * A value of "1" indicates that the backend can process requests
+ * containing the BLKIF_OP_DISCARD request opcode. Requests
+ * of this type may still be returned at any time with the
+ * BLKIF_RSP_EOPNOTSUPP result code.
+ *
+ * feature-persistent
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ * Notes: 7
+ *
+ * A value of "1" indicates that the backend can keep the grants used
+ * by the frontend driver mapped, so the same set of grants should be
+ * used in all transactions. The maximum number of grants the backend
+ * can map persistently depends on the implementation, but ideally it
+ * should be RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST. Using this
+ * feature the backend doesn't need to unmap each grant, preventing
+ * costly TLB flushes. The backend driver should only map grants
+ * persistently if the frontend supports it. If a backend driver chooses
+ * to use the persistent protocol when the frontend doesn't support it,
+ * it will probably hit the maximum number of persistently mapped grants
+ * (due to the fact that the frontend won't be reusing the same grants),
+ * and fall back to non-persistent mode. Backend implementations may
+ * shrink or expand the number of persistently mapped grants without
+ * notifying the frontend depending on memory constraints (this might
+ * cause a performance degradation).
+ *
+ * If a backend driver wants to limit the maximum number of persistently
+ * mapped grants to a value less than RING_SIZE *
+ * BLKIF_MAX_SEGMENTS_PER_REQUEST a LRU strategy should be used to
+ * discard the grants that are less commonly used. Using a LRU in the
+ * backend driver paired with a LIFO queue in the frontend will
+ * allow us to have better performance in this scenario.
+ *
+ *----------------------- Request Transport Parameters ------------------------
+ *
+ * max-ring-page-order
+ * Values: <uint32_t>
+ * Default Value: 0
+ * Notes: 1, 3
+ *
+ * The maximum supported size of the request ring buffer in units of
+ * lb(machine pages). (e.g. 0 == 1 page, 1 = 2 pages, 2 == 4 pages,
+ * etc.).
+ *
+ * max-ring-pages
+ * Values: <uint32_t>
+ * Default Value: 1
+ * Notes: DEPRECATED, 2, 3
+ *
+ * The maximum supported size of the request ring buffer in units of
+ * machine pages. The value must be a power of 2.
+ *
+ *------------------------- Backend Device Properties -------------------------
+ *
+ * discard-enable
+ * Values: 0/1 (boolean)
+ * Default Value: 1
+ *
+ * This optional property, set by the toolstack, instructs the backend
+ * to offer (or not to offer) discard to the frontend. If the property
+ * is missing the backend should offer discard if the backing storage
+ * actually supports it.
+ *
+ * discard-alignment
+ * Values: <uint32_t>
+ * Default Value: 0
+ * Notes: 4, 5
+ *
+ * The offset, in bytes from the beginning of the virtual block device,
+ * to the first, addressable, discard extent on the underlying device.
+ *
+ * discard-granularity
+ * Values: <uint32_t>
+ * Default Value: <"sector-size">
+ * Notes: 4
+ *
+ * The size, in bytes, of the individually addressable discard extents
+ * of the underlying device.
+ *
+ * discard-secure
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ * Notes: 10
+ *
+ * A value of "1" indicates that the backend can process BLKIF_OP_DISCARD
+ * requests with the BLKIF_DISCARD_SECURE flag set.
+ *
+ * info
+ * Values: <uint32_t> (bitmap)
+ *
+ * A collection of bit flags describing attributes of the backing
+ * device. The VDISK_* macros define the meaning of each bit
+ * location.
+ *
+ * sector-size
+ * Values: <uint32_t>
+ *
+ * The logical block size, in bytes, of the underlying storage. This
+ * must be a power of two with a minimum value of 512.
+ *
+ * NOTE: Because of implementation bugs in some frontends this must be
+ * set to 512, unless the frontend advertizes a non-zero value
+ * in its "feature-large-sector-size" xenbus node. (See below).
+ *
+ * physical-sector-size
+ * Values: <uint32_t>
+ * Default Value: <"sector-size">
+ *
+ * The physical block size, in bytes, of the backend storage. This
+ * must be an integer multiple of "sector-size".
+ *
+ * sectors
+ * Values: <uint64_t>
+ *
+ * The size of the backend device, expressed in units of "sector-size".
+ * The product of "sector-size" and "sectors" must also be an integer
+ * multiple of "physical-sector-size", if that node is present.
+ *
+ *****************************************************************************
+ * Frontend XenBus Nodes
+ *****************************************************************************
+ *
+ *----------------------- Request Transport Parameters -----------------------
+ *
+ * event-channel
+ * Values: <uint32_t>
+ *
+ * The identifier of the Xen event channel used to signal activity
+ * in the ring buffer.
+ *
+ * ring-ref
+ * Values: <uint32_t>
+ * Notes: 6
+ *
+ * The Xen grant reference granting permission for the backend to map
+ * the sole page in a single page sized ring buffer.
+ *
+ * ring-ref%u
+ * Values: <uint32_t>
+ * Notes: 6
+ *
+ * For a frontend providing a multi-page ring, a "number of ring pages"
+ * sized list of nodes, each containing a Xen grant reference granting
+ * permission for the backend to map the page of the ring located
+ * at page index "%u". Page indexes are zero based.
+ *
+ * protocol
+ * Values: string (XEN_IO_PROTO_ABI_*)
+ * Default Value: XEN_IO_PROTO_ABI_NATIVE
+ *
+ * The machine ABI rules governing the format of all ring request and
+ * response structures.
+ *
+ * ring-page-order
+ * Values: <uint32_t>
+ * Default Value: 0
+ * Maximum Value: MAX(ffs(max-ring-pages) - 1, max-ring-page-order)
+ * Notes: 1, 3
+ *
+ * The size of the frontend allocated request ring buffer in units
+ * of lb(machine pages). (e.g. 0 == 1 page, 1 = 2 pages, 2 == 4 pages,
+ * etc.).
+ *
+ * num-ring-pages
+ * Values: <uint32_t>
+ * Default Value: 1
+ * Maximum Value: MAX(max-ring-pages,(0x1 << max-ring-page-order))
+ * Notes: DEPRECATED, 2, 3
+ *
+ * The size of the frontend allocated request ring buffer in units of
+ * machine pages. The value must be a power of 2.
+ *
+ *--------------------------------- Features ---------------------------------
+ *
+ * feature-persistent
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ * Notes: 7, 8, 9
+ *
+ * A value of "1" indicates that the frontend will reuse the same grants
+ * for all transactions, allowing the backend to map them with write
+ * access (even when it should be read-only). If the frontend hits the
+ * maximum number of allowed persistently mapped grants, it can fallback
+ * to non persistent mode. This will cause a performance degradation,
+ * since the backend driver will still try to map those grants
+ * persistently. Since the persistent grants protocol is compatible with
+ * the previous protocol, a frontend driver can choose to work in
+ * persistent mode even when the backend doesn't support it.
+ *
+ * It is recommended that the frontend driver stores the persistently
+ * mapped grants in a LIFO queue, so a subset of all persistently mapped
+ * grants gets used commonly. This is done in case the backend driver
+ * decides to limit the maximum number of persistently mapped grants
+ * to a value less than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST.
+ *
+ * feature-large-sector-size
+ * Values: 0/1 (boolean)
+ * Default Value: 0
+ *
+ * A value of "1" indicates that the frontend will correctly supply and
+ * interpret all sector-based quantities in terms of the "sector-size"
+ * value supplied in the backend info, whatever that may be set to.
+ * If this node is not present or its value is "0" then it is assumed
+ * that the frontend requires that the logical block size is 512 as it
+ * is hardcoded (which is the case in some frontend implementations).
+ *
+ *------------------------- Virtual Device Properties -------------------------
+ *
+ * device-type
+ * Values: "disk", "cdrom", "floppy", etc.
+ *
+ * virtual-device
+ * Values: <uint32_t>
+ *
+ * A value indicating the physical device to virtualize within the
+ * frontend's domain. (e.g. "The first ATA disk", "The third SCSI
+ * disk", etc.)
+ *
+ * See docs/misc/vbd-interface.txt for details on the format of this
+ * value.
+ *
+ * Notes
+ * -----
+ * (1) Multi-page ring buffer scheme first developed in the Citrix XenServer
+ * PV drivers.
+ * (2) Multi-page ring buffer scheme first used in some RedHat distributions
+ * including a distribution deployed on certain nodes of the Amazon
+ * EC2 cluster.
+ * (3) Support for multi-page ring buffers was implemented independently,
+ * in slightly different forms, by both Citrix and RedHat/Amazon.
+ * For full interoperability, block front and backends should publish
+ * identical ring parameters, adjusted for unit differences, to the
+ * XenStore nodes used in both schemes.
+ * (4) Devices that support discard functionality may internally allocate space
+ * (discardable extents) in units that are larger than the exported logical
+ * block size. If the backing device has such discardable extents the
+ * backend should provide both discard-granularity and discard-alignment.
+ * Providing just one of the two may be considered an error by the frontend.
+ * Backends supporting discard should include discard-granularity and
+ * discard-alignment even if it supports discarding individual sectors.
+ * Frontends should assume discard-alignment == 0 and discard-granularity
+ * == sector size if these keys are missing.
+ * (5) The discard-alignment parameter allows a physical device to be
+ * partitioned into virtual devices that do not necessarily begin or
+ * end on a discardable extent boundary.
+ * (6) When there is only a single page allocated to the request ring,
+ * 'ring-ref' is used to communicate the grant reference for this
+ * page to the backend. When using a multi-page ring, the 'ring-ref'
+ * node is not created. Instead 'ring-ref0' - 'ring-refN' are used.
+ * (7) When using persistent grants data has to be copied from/to the page
+ * where the grant is currently mapped. The overhead of doing this copy
+ * however doesn't suppress the speed improvement of not having to unmap
+ * the grants.
+ * (8) The frontend driver has to allow the backend driver to map all grants
+ * with write access, even when they should be mapped read-only, since
+ * further requests may reuse these grants and require write permissions.
+ * (9) Linux implementation doesn't have a limit on the maximum number of
+ * grants that can be persistently mapped in the frontend driver, but
+ * due to the frontent driver implementation it should never be bigger
+ * than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST.
+ *(10) The discard-secure property may be present and will be set to 1 if the
+ * backing device supports secure discard.
+ *(11) Only used by Linux and NetBSD.
+ */
+
+/*
+ * Multiple hardware queues/rings:
+ * If supported, the backend will write the key "multi-queue-max-queues" to
+ * the directory for that vbd, and set its value to the maximum supported
+ * number of queues.
+ * Frontends that are aware of this feature and wish to use it can write the
+ * key "multi-queue-num-queues" with the number they wish to use, which must be
+ * greater than zero, and no more than the value reported by the backend in
+ * "multi-queue-max-queues".
+ *
+ * For frontends requesting just one queue, the usual event-channel and
+ * ring-ref keys are written as before, simplifying the backend processing
+ * to avoid distinguishing between a frontend that doesn't understand the
+ * multi-queue feature, and one that does, but requested only one queue.
+ *
+ * Frontends requesting two or more queues must not write the toplevel
+ * event-channel and ring-ref keys, instead writing those keys under sub-keys
+ * having the name "queue-N" where N is the integer ID of the queue/ring for
+ * which those keys belong. Queues are indexed from zero.
+ * For example, a frontend with two queues must write the following set of
+ * queue-related keys:
+ *
+ * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"
+ * /local/domain/1/device/vbd/0/queue-0 = ""
+ * /local/domain/1/device/vbd/0/queue-0/ring-ref = "<ring-ref#0>"
+ * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"
+ * /local/domain/1/device/vbd/0/queue-1 = ""
+ * /local/domain/1/device/vbd/0/queue-1/ring-ref = "<ring-ref#1>"
+ * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"
+ *
+ * It is also possible to use multiple queues/rings together with
+ * feature multi-page ring buffer.
+ * For example, a frontend requests two queues/rings and the size of each ring
+ * buffer is two pages must write the following set of related keys:
+ *
+ * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"
+ * /local/domain/1/device/vbd/0/ring-page-order = "1"
+ * /local/domain/1/device/vbd/0/queue-0 = ""
+ * /local/domain/1/device/vbd/0/queue-0/ring-ref0 = "<ring-ref#0>"
+ * /local/domain/1/device/vbd/0/queue-0/ring-ref1 = "<ring-ref#1>"
+ * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"
+ * /local/domain/1/device/vbd/0/queue-1 = ""
+ * /local/domain/1/device/vbd/0/queue-1/ring-ref0 = "<ring-ref#2>"
+ * /local/domain/1/device/vbd/0/queue-1/ring-ref1 = "<ring-ref#3>"
+ * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"
+ *
+ */
+
+/*
+ * STATE DIAGRAMS
+ *
+ *****************************************************************************
+ * Startup *
+ *****************************************************************************
+ *
+ * Tool stack creates front and back nodes with state XenbusStateInitialising.
+ *
+ * Front Back
+ * ================================= =====================================
+ * XenbusStateInitialising XenbusStateInitialising
+ * o Query virtual device o Query backend device identification
+ * properties. data.
+ * o Setup OS device instance. o Open and validate backend device.
+ * o Publish backend features and
+ * transport parameters.
+ * |
+ * |
+ * V
+ * XenbusStateInitWait
+ *
+ * o Query backend features and
+ * transport parameters.
+ * o Allocate and initialize the
+ * request ring.
+ * o Publish transport parameters
+ * that will be in effect during
+ * this connection.
+ * |
+ * |
+ * V
+ * XenbusStateInitialised
+ *
+ * o Query frontend transport parameters.
+ * o Connect to the request ring and
+ * event channel.
+ * o Publish backend device properties.
+ * |
+ * |
+ * V
+ * XenbusStateConnected
+ *
+ * o Query backend device properties.
+ * o Finalize OS virtual device
+ * instance.
+ * |
+ * |
+ * V
+ * XenbusStateConnected
+ *
+ * Note: Drivers that do not support any optional features, or the negotiation
+ * of transport parameters, can skip certain states in the state machine:
+ *
+ * o A frontend may transition to XenbusStateInitialised without
+ * waiting for the backend to enter XenbusStateInitWait. In this
+ * case, default transport parameters are in effect and any
+ * transport parameters published by the frontend must contain
+ * their default values.
+ *
+ * o A backend may transition to XenbusStateInitialised, bypassing
+ * XenbusStateInitWait, without waiting for the frontend to first
+ * enter the XenbusStateInitialised state. In this case, default
+ * transport parameters are in effect and any transport parameters
+ * published by the backend must contain their default values.
+ *
+ * Drivers that support optional features and/or transport parameter
+ * negotiation must tolerate these additional state transition paths.
+ * In general this means performing the work of any skipped state
+ * transition, if it has not already been performed, in addition to the
+ * work associated with entry into the current state.
+ */
+
+/*
+ * REQUEST CODES.
+ */
+#define BLKIF_OP_READ 0
+#define BLKIF_OP_WRITE 1
+/*
+ * All writes issued prior to a request with the BLKIF_OP_WRITE_BARRIER
+ * operation code ("barrier request") must be completed prior to the
+ * execution of the barrier request. All writes issued after the barrier
+ * request must not execute until after the completion of the barrier request.
+ *
+ * Optional. See "feature-barrier" XenBus node documentation above.
+ */
+#define BLKIF_OP_WRITE_BARRIER 2
+/*
+ * Commit any uncommitted contents of the backing device's volatile cache
+ * to stable storage.
+ *
+ * Optional. See "feature-flush-cache" XenBus node documentation above.
+ */
+#define BLKIF_OP_FLUSH_DISKCACHE 3
+/*
+ * Used in SLES sources for device specific command packet
+ * contained within the request. Reserved for that purpose.
+ */
+#define BLKIF_OP_RESERVED_1 4
+/*
+ * Indicate to the backend device that a region of storage is no longer in
+ * use, and may be discarded at any time without impact to the client. If
+ * the BLKIF_DISCARD_SECURE flag is set on the request, all copies of the
+ * discarded region on the device must be rendered unrecoverable before the
+ * command returns.
+ *
+ * This operation is analogous to performing a trim (ATA) or unamp (SCSI),
+ * command on a native device.
+ *
+ * More information about trim/unmap operations can be found at:
+ * http://t13.org/Documents/UploadedDocuments/docs2008/
+ * e07154r6-Data_Set_Management_Proposal_for_ATA-ACS2.doc
+ * http://www.seagate.com/staticfiles/support/disc/manuals/
+ * Interface%20manuals/100293068c.pdf
+ *
+ * Optional. See "feature-discard", "discard-alignment",
+ * "discard-granularity", and "discard-secure" in the XenBus node
+ * documentation above.
+ */
+#define BLKIF_OP_DISCARD 5
+
+/*
+ * Recognized if "feature-max-indirect-segments" in present in the backend
+ * xenbus info. The "feature-max-indirect-segments" node contains the maximum
+ * number of segments allowed by the backend per request. If the node is
+ * present, the frontend might use blkif_request_indirect structs in order to
+ * issue requests with more than BLKIF_MAX_SEGMENTS_PER_REQUEST (11). The
+ * maximum number of indirect segments is fixed by the backend, but the
+ * frontend can issue requests with any number of indirect segments as long as
+ * it's less than the number provided by the backend. The indirect_grefs field
+ * in blkif_request_indirect should be filled by the frontend with the
+ * grant references of the pages that are holding the indirect segments.
+ * These pages are filled with an array of blkif_request_segment that hold the
+ * information about the segments. The number of indirect pages to use is
+ * determined by the number of segments an indirect request contains. Every
+ * indirect page can contain a maximum of
+ * (PAGE_SIZE / sizeof(struct blkif_request_segment)) segments, so to
+ * calculate the number of indirect pages to use we have to do
+ * ceil(indirect_segments / (PAGE_SIZE / sizeof(struct blkif_request_segment))).
+ *
+ * If a backend does not recognize BLKIF_OP_INDIRECT, it should *not*
+ * create the "feature-max-indirect-segments" node!
+ */
+#define BLKIF_OP_INDIRECT 6
+
+/*
+ * Maximum scatter/gather segments per request.
+ * This is carefully chosen so that sizeof(blkif_ring_t) <= PAGE_SIZE.
+ * NB. This could be 12 if the ring indexes weren't stored in the same page.
+ */
+#define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
+
+/*
+ * Maximum number of indirect pages to use per request.
+ */
+#define BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST 8
+
+/*
+ * NB. 'first_sect' and 'last_sect' in blkif_request_segment, as well as
+ * 'sector_number' in blkif_request, blkif_request_discard and
+ * blkif_request_indirect are sector-based quantities. See the description
+ * of the "feature-large-sector-size" frontend xenbus node above for
+ * more information.
+ */
+struct blkif_request_segment {
+ grant_ref_t gref; /* reference to I/O buffer frame */
+ /* @first_sect: first sector in frame to transfer (inclusive). */
+ /* @last_sect: last sector in frame to transfer (inclusive). */
+ uint8_t first_sect, last_sect;
+};
+
+/*
+ * Starting ring element for any I/O request.
+ */
+struct blkif_request {
+ uint8_t operation; /* BLKIF_OP_??? */
+ uint8_t nr_segments; /* number of segments */
+ blkif_vdev_t handle; /* only for read/write requests */
+ uint64_t id; /* private guest value, echoed in resp */
+ blkif_sector_t sector_number;/* start sector idx on disk (r/w only) */
+ struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+};
+typedef struct blkif_request blkif_request_t;
+
+/*
+ * Cast to this structure when blkif_request.operation == BLKIF_OP_DISCARD
+ * sizeof(struct blkif_request_discard) <= sizeof(struct blkif_request)
+ */
+struct blkif_request_discard {
+ uint8_t operation; /* BLKIF_OP_DISCARD */
+ uint8_t flag; /* BLKIF_DISCARD_SECURE or zero */
+#define BLKIF_DISCARD_SECURE (1<<0) /* ignored if discard-secure=0 */
+ blkif_vdev_t handle; /* same as for read/write requests */
+ uint64_t id; /* private guest value, echoed in resp */
+ blkif_sector_t sector_number;/* start sector idx on disk */
+ uint64_t nr_sectors; /* number of contiguous sectors to discard*/
+};
+typedef struct blkif_request_discard blkif_request_discard_t;
+
+struct blkif_request_indirect {
+ uint8_t operation; /* BLKIF_OP_INDIRECT */
+ uint8_t indirect_op; /* BLKIF_OP_{READ/WRITE} */
+ uint16_t nr_segments; /* number of segments */
+ uint64_t id; /* private guest value, echoed in resp */
+ blkif_sector_t sector_number;/* start sector idx on disk (r/w only) */
+ blkif_vdev_t handle; /* same as for read/write requests */
+ grant_ref_t indirect_grefs[BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST];
+#ifdef __i386__
+ uint64_t pad; /* Make it 64 byte aligned on i386 */
+#endif
+};
+typedef struct blkif_request_indirect blkif_request_indirect_t;
+
+struct blkif_response {
+ uint64_t id; /* copied from request */
+ uint8_t operation; /* copied from request */
+ int16_t status; /* BLKIF_RSP_??? */
+};
+typedef struct blkif_response blkif_response_t;
+
+/*
+ * STATUS RETURN CODES.
+ */
+ /* Operation not supported (only happens on barrier writes). */
+#define BLKIF_RSP_EOPNOTSUPP -2
+ /* Operation failed for some unspecified reason (-EIO). */
+#define BLKIF_RSP_ERROR -1
+ /* Operation completed successfully. */
+#define BLKIF_RSP_OKAY 0
+
+/*
+ * Generate blkif ring structures and types.
+ */
+DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
+
+#define VDISK_CDROM 0x1
+#define VDISK_REMOVABLE 0x2
+#define VDISK_READONLY 0x4
+
+#endif /* __XEN_PUBLIC_IO_BLKIF_H__ */