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
  27 typedef uint16_t blkif_vdev_t;
  28 typedef 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
  54 struct 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
  68 struct 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
  88 DEFINE_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__ */