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[win-pv-devel] [RFC PATCH 1/6] Update blkif.h



Pull the latest blkif.h from xen.git at
0d16ece0c5adb960ee4e45f12183bcac8fe6d50a

Signed-off-by: owensm <owen.smith@xxxxxxxxxx>
---
 include/xen/io/blkif.h | 1100 ++++++++++++++++++++++++++----------------------
 1 file changed, 597 insertions(+), 503 deletions(-)

diff --git a/include/xen/io/blkif.h b/include/xen/io/blkif.h
index c3e169c..f659881 100644
--- a/include/xen/io/blkif.h
+++ b/include/xen/io/blkif.h
@@ -1,29 +1,29 @@
 /******************************************************************************
- * 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
- */
+* 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__
@@ -32,16 +32,16 @@
 #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()).
- */
+* 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
@@ -49,487 +49,581 @@
 #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
- *      backend driver to open the backing device.  (e.g. the path to the
- *      file or block device representing the backing store.)
- *
- * 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.
- *
- * 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-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 sector size, in bytes, of the backend device.
- *
- * physical-sector-size
- *      Values:         <uint32_t>
- *
- *      The physical sector size, in bytes, of the backend device.
- *
- * sectors
- *      Values:         <uint64_t>
- *
- *      The size of the backend device, expressed in units of its logical
- *      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.
- *
- * 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 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.
- *
- *------------------------- 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.
- */
+* 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 sector size, in bytes, of the backend device.
+*
+* physical-sector-size
+*      Values:         <uint32_t>
+*
+*      The physical sector size, in bytes, of the backend device.
+*
+* sectors
+*      Values:         <uint64_t>
+*
+*      The size of the backend device, expressed in units of its logical
+*      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.
+*
+* 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 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.
+*
+*------------------------- 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.
+*/
 
 /*
- * 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.
- */
+* 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>"
+*
+*/
 
 /*
- * REQUEST CODES.
- */
+* 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.
- */
+* 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.
- */
+* 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.
- */
+* 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.
- */
+* 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!
- */
+* 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.
- */
+* 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.
- */
+* 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, 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 "physical-sector-size" node in
- * the backend xenbus info. Also the xenbus "sectors" node is expressed in
- * 512-byte units.
- */
+* 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 "physical-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).     */
+                             /* @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.
- */
+* Starting ring element for any I/O request.
+*/
 struct blkif_request {
     uint8_t        operation;    /* BLKIF_OP_???                         */
     uint8_t        nr_segments;  /* number of segments                   */
@@ -541,9 +635,9 @@ struct blkif_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)
- */
+* 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         */
@@ -577,18 +671,18 @@ struct blkif_response {
 typedef struct blkif_response blkif_response_t;
 
 /*
- * STATUS RETURN CODES.
- */
- /* Operation not supported (only happens on barrier writes). */
+* STATUS RETURN CODES.
+*/
+/* Operation not supported (only happens on barrier writes). */
 #define BLKIF_RSP_EOPNOTSUPP  -2
- /* Operation failed for some unspecified reason (-EIO). */
+/* Operation failed for some unspecified reason (-EIO). */
 #define BLKIF_RSP_ERROR       -1
- /* Operation completed successfully. */
+/* Operation completed successfully. */
 #define BLKIF_RSP_OKAY         0
 
 /*
- * Generate blkif ring structures and types.
- */
+* Generate blkif ring structures and types.
+*/
 DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
 
 #define VDISK_CDROM        0x1
@@ -598,11 +692,11 @@ DEFINE_RING_TYPES(blkif, struct blkif_request, struct 
blkif_response);
 #endif /* __XEN_PUBLIC_IO_BLKIF_H__ */
 
 /*
- * Local variables:
- * mode: C
- * c-file-style: "BSD"
- * c-basic-offset: 4
- * tab-width: 4
- * indent-tabs-mode: nil
- * End:
- */
+* Local variables:
+* mode: C
+* c-file-style: "BSD"
+* c-basic-offset: 4
+* tab-width: 4
+* indent-tabs-mode: nil
+* End:
+*/
-- 
2.16.2.windows.1


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