/******************************************************************************
* 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
* backend driver to open the backing device. (e.g. the path to the
* file or block device representing the backing store.)
*
* physical-device
* Values: "MAJOR:MINOR"
*
* MAJOR and MINOR are the major number and minor number of the
* backing device respectively.
*
* 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 discard to the frontend. If the property is missing the
* backend should offer discard if the backing storage actually supports
* it. This optional property, set by the toolstack, requests that the
* backend offer, or not offer, discard to the frontend.
*
* 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.
*/
/*
* 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, 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). */
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__ */
/*
* Local variables:
* mode: C
* c-file-style: "BSD"
* c-basic-offset: 4
* tab-width: 4
* indent-tabs-mode: nil
* End:
*/