LXR linux/include/xen/interface/io/blkif.h

   1/******************************************************************************
   2 * blkif.h
   3 *
   4 * Unified block-device I/O interface for Xen guest OSes.
   5 *
   6 * Copyright (c) 2003-2004, Keir Fraser
   7 */
   8
   9#ifndef __XEN_PUBLIC_IO_BLKIF_H__
  10#define __XEN_PUBLIC_IO_BLKIF_H__
  11
  12#include "ring.h"
  13#include "../grant_table.h"
  14
  15/*
  16 * Front->back notifications: When enqueuing a new request, sending a
  17 * notification can be made conditional on req_event (i.e., the generic
  18 * hold-off mechanism provided by the ring macros). Backends must set
  19 * req_event appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
  20 *
  21 * Back->front notifications: When enqueuing a new response, sending a
  22 * notification can be made conditional on rsp_event (i.e., the generic
  23 * hold-off mechanism provided by the ring macros). Frontends must set
  24 * rsp_event appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
  25 */
  26
  27typedef uint16_t blkif_vdev_t;
  28typedef uint64_t blkif_sector_t;
  29
  30/*
  31 * REQUEST CODES.
  32 */
  33#define BLKIF_OP_READ              0
  34#define BLKIF_OP_WRITE             1
  35/*
  36 * Recognised only if "feature-barrier" is present in backend xenbus info.
  37 * The "feature_barrier" node contains a boolean indicating whether barrier
  38 * requests are likely to succeed or fail. Either way, a barrier request
  39 * may fail at any time with BLKIF_RSP_EOPNOTSUPP if it is unsupported by
  40 * the underlying block-device hardware. The boolean simply indicates whether
  41 * or not it is worthwhile for the frontend to attempt barrier requests.
  42 * If a backend does not recognise BLKIF_OP_WRITE_BARRIER, it should *not*
  43 * create the "feature-barrier" node!
  44 */
  45#define BLKIF_OP_WRITE_BARRIER     2
  46
  47/*
  48 * Maximum scatter/gather segments per request.
  49 * This is carefully chosen so that sizeof(struct blkif_ring) <= PAGE_SIZE.
  50 * NB. This could be 12 if the ring indexes weren't stored in the same page.
  51 */
  52#define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
  53
  54struct blkif_request {
  55        uint8_t        operation;    /* BLKIF_OP_???                         */
  56        uint8_t        nr_segments;  /* number of segments                   */
  57        blkif_vdev_t   handle;       /* only for read/write requests         */
  58        uint64_t       id;           /* private guest value, echoed in resp  */
  59        blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
  60        struct blkif_request_segment {
  61                grant_ref_t gref;        /* reference to I/O buffer frame        */
  62                /* @first_sect: first sector in frame to transfer (inclusive).   */
  63                /* @last_sect: last sector in frame to transfer (inclusive).     */
  64                uint8_t     first_sect, last_sect;
  65        } seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
  66};
  67
  68struct blkif_response {
  69        uint64_t        id;              /* copied from request */
  70        uint8_t         operation;       /* copied from request */
  71        int16_t         status;          /* BLKIF_RSP_???       */
  72};
  73
  74/*
  75 * STATUS RETURN CODES.
  76 */
  77 /* Operation not supported (only happens on barrier writes). */
  78#define BLKIF_RSP_EOPNOTSUPP  -2
  79 /* Operation failed for some unspecified reason (-EIO). */
  80#define BLKIF_RSP_ERROR       -1
  81 /* Operation completed successfully. */
  82#define BLKIF_RSP_OKAY         0
  83
  84/*
  85 * Generate blkif ring structures and types.
  86 */
  87
  88DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
  89
  90#define VDISK_CDROM        0x1
  91#define VDISK_REMOVABLE    0x2
  92#define VDISK_READONLY     0x4
  93
  94#endif /* __XEN_PUBLIC_IO_BLKIF_H__ */
  95