/****************************************************************************** * 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: * 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: * 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: * 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: * 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: (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: * * The logical sector size, in bytes, of the backend device. * * physical-sector-size * Values: * * The physical sector size, in bytes, of the backend device. * * sectors * Values: * * 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: * * The identifier of the Xen event channel used to signal activity * in the ring buffer. * * ring-ref * Values: * 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: * 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: * 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: * 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 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: * * 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: */