FreeBSD/Linux Kernel Cross Reference
sys/xen/interface/io/blkif.h

     /******************************************************************************
      * 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 formatted 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
     *
     *      Data used by the backend driver to locate and configure the backing
     *      device.  The format and semantics of this data vary according to the
     *      backing device in use and are outside the scope of this specification.
     *
     * type
     *      Values:         "file", "phy", "tap"
     *
     *      The type of the backing device/object.
     *
    *--------------------------------- 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.
    *
    *----------------------- 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.
    *
    * max-requests         <uint32_t>
    *      Default Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE)
    *      Maximum Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE * max-ring-pages)
    *
    *      The maximum number of concurrent, logical requests supported by
    *      the backend.
    *
    *      Note: A logical request may span multiple ring entries.
    *
    * max-request-segments
    *      Values:         <uint8_t>
    *      Default Value:  BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK
    *      Maximum Value:  BLKIF_MAX_SEGMENTS_PER_REQUEST
    *
    *      The maximum value of blkif_request.nr_segments supported by
    *      the backend.
    *
    * max-request-size
    *      Values:         <uint32_t>
    *      Default Value:  BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK * PAGE_SIZE
    *      Maximum Value:  BLKIF_MAX_SEGMENTS_PER_REQUEST * PAGE_SIZE
    *
    *      The maximum amount of data, in bytes, that can be referenced by a
    *      request type that accesses frontend memory (currently BLKIF_OP_READ,
    *      BLKIF_OP_WRITE, or BLKIF_OP_WRITE_BARRIER).
    *
    *------------------------- Backend Device Properties -------------------------
    *
    * 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
    *
    *      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 size, in bytes, of the individually addressible data blocks
    *      on the backend device.
    *
    * sectors
    *      Values:         <uint64_t>
    *
    *      The size of the backend device, expressed in units of its native
    *      sector size ("sector-size").
    *
    *****************************************************************************
    *                            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.
    *
    * max-requests
    *      Values:         <uint32_t>
    *      Default Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE)
    *      Maximum Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE * max-ring-pages)
    *
    *      The maximum number of concurrent, logical requests that will be
    *      issued by the frontend.
    *
    *      Note: A logical request may span multiple ring entries.
    *
    * max-request-segments
    *      Values:         <uint8_t>
    *      Default Value:  BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK
    *      Maximum Value:  MIN(255, backend/max-request-segments)
    *
    *      The maximum value the frontend will set in the
    *      blkif_request.nr_segments field.
    *
    * max-request-size
    *      Values:         <uint32_t>
    *      Default Value:  BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK * PAGE_SIZE
    *      Maximum Value:  max-request-segments * PAGE_SIZE
    *
    *      The maximum amount of data, in bytes, that can be referenced by
    *      a request type that accesses frontend memory (currently BLKIF_OP_READ,
    *      BLKIF_OP_WRITE, or BLKIF_OP_WRITE_BARRIER).
    *
    *------------------------- 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 Red Hat 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 Red Hat/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.
    * (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.
    */
   
   /*
    * 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 unmap (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
   
   /*
    * Maximum scatter/gather segments associated with a request header block.
    * 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_HEADER_BLOCK  11
   
   /*
    * Maximum scatter/gather segments associated with a segment block.
    */
   #define BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK 14
   
   /*
    * Maximum scatter/gather segments per request (header + segment blocks).
    */
   #define BLKIF_MAX_SEGMENTS_PER_REQUEST 255
   
   /*
    * NB. first_sect and last_sect in blkif_request_segment, as well as
    * sector_number in blkif_request, are always expressed in 512-byte units.
    * However they must be properly aligned to the real sector size of the
    * physical disk, which is reported in the "sector-size" node in the backend
    * xenbus info. Also the xenbus "sectors" node is expressed in 512-byte units.
    */
   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;
   };
   typedef struct blkif_request_segment blkif_request_segment_t;
   
   /*
    * Starting ring element for any I/O request.
    *
    * One or more segment blocks can be inserted into the request ring
    * just after a blkif_request_t, allowing requests to operate on
    * up to BLKIF_MAX_SEGMENTS_PER_REQUEST.
    *
    * BLKIF_SEGS_TO_BLOCKS() can be used on blkif_requst.nr_segments
    * to determine the number of contiguous ring entries associated
    * with this request.
    *
    * Note:  Due to the way Xen request rings operate, the producer and
    *        consumer indices of the ring must be incremented by the
    *        BLKIF_SEGS_TO_BLOCKS() value of the associated request.
    *        (e.g. a response to a 3 ring entry request must also consume
    *        3 entries in the ring, even though only the first ring entry
    *        in the response has any data.)
    */
   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)  */
       blkif_request_segment_t seg[BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK];
   };
   typedef struct blkif_request blkif_request_t;
   
   /*
    * A segment block is a ring request structure that contains only
    * segment data.
    *
    * sizeof(struct blkif_segment_block) <= sizeof(struct blkif_request)
    */
   struct blkif_segment_block {
       blkif_request_segment_t seg[BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK];
   };
   typedef struct blkif_segment_block blkif_segment_block_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_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);
   
   /*
    * Index to, and treat as a segment block, an entry in the ring.
    */
   #define BLKRING_GET_SEG_BLOCK(_r, _idx)                                 \
       (((blkif_segment_block_t *)RING_GET_REQUEST(_r, _idx))->seg)
   
   /*
    * The number of ring request blocks required to handle an I/O
    * request containing _segs segments.
    */
   #define BLKIF_SEGS_TO_BLOCKS(_segs)                                     \
       ((((_segs - BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK)                    \
        + (BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK - 1))                      \
       / BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK) + /*header_block*/1)
   
   #define VDISK_CDROM        0x1
   #define VDISK_REMOVABLE    0x2
   #define VDISK_READONLY     0x4
   
   #endif /* __XEN_PUBLIC_IO_BLKIF_H__ */
   
   /*
    * Local variables:
    * mode: C
    * c-set-style: "BSD"
    * c-basic-offset: 4
    * tab-width: 4
    * indent-tabs-mode: nil
    * End:
    */

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