xen: Add Xen pvSCSI protocol description

/******************************************************************************

 * vscsiif.h

 *

 * Based on the blkif.h code.

 *

 * 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) FUJITSU Limited 2008.

 */

#ifndef __XEN__PUBLIC_IO_SCSI_H__

#define __XEN__PUBLIC_IO_SCSI_H__

#include "ring.h"

#include "../grant_table.h"

/*

 * Feature and Parameter Negotiation

 * =================================

 * The two halves of a Xen pvSCSI 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.

 *

 * 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.

 *

 *****************************************************************************

 *                            Backend XenBus Nodes

 *****************************************************************************

 *

 *------------------ Backend Device Identification (PRIVATE) ------------------

 *

 * p-devname

 *      Values:         string

 *

 *      A free string used to identify the physical device (e.g. a disk name).

 *

 * p-dev

 *      Values:         string

 *

 *      A string specifying the backend device: either a 4-tuple "h:c:t:l"

 *      (host, controller, target, lun, all integers), or a WWN (e.g.

 *      "naa.60014054ac780582").

 *

 * v-dev

 *      Values:         string

 *

 *      A string specifying the frontend device in form of a 4-tuple "h:c:t:l"

 *      (host, controller, target, lun, all integers).

 *

 *--------------------------------- Features ---------------------------------

 *

 * feature-sg-grant

 *      Values:         unsigned [VSCSIIF_SG_TABLESIZE...65535]

 *      Default Value:  0

 *

 *      Specifies the maximum number of scatter/gather elements in grant pages

 *      supported. If not set, the backend supports up to VSCSIIF_SG_TABLESIZE

 *      SG elements specified directly in the request.

 *

 *****************************************************************************

 *                            Frontend XenBus Nodes

 *****************************************************************************

 *

 *----------------------- Request Transport Parameters -----------------------

 *

 * event-channel

 *      Values:         unsigned

 *

 *      The identifier of the Xen event channel used to signal activity

 *      in the ring buffer.

 *

 * ring-ref

 *      Values:         unsigned

 *

 *      The Xen grant reference granting permission for the backend to map

 *      the sole page in a single page sized ring buffer.

 *

 * 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.

 */

/* Requests from the frontend to the backend */

/*

 * Request a SCSI operation specified via a CDB in vscsiif_request.cmnd.

 * The target is specified via channel, id and lun.

 *

 * The operation to be performed is specified via a CDB in cmnd[], the length

 * of the CDB is in cmd_len. sc_data_direction specifies the direction of data

 * (to the device, from the device, or none at all).

 *

 * If data is to be transferred to or from the device the buffer(s) in the

 * guest memory is/are specified via one or multiple scsiif_request_segment

 * descriptors each specifying a memory page via a grant_ref_t, a offset into

 * the page and the length of the area in that page. All scsiif_request_segment

 * areas concatenated form the resulting data buffer used by the operation.

 * If the number of scsiif_request_segment areas is not too large (less than

 * or equal VSCSIIF_SG_TABLESIZE) the areas can be specified directly in the

 * seg[] array and the number of valid scsiif_request_segment elements is to be

 * set in nr_segments.

 *

 * If "feature-sg-grant" in the Xenstore is set it is possible to specify more

 * than VSCSIIF_SG_TABLESIZE scsiif_request_segment elements via indirection.

 * The maximum number of allowed scsiif_request_segment elements is the value

 * of the "feature-sg-grant" entry from Xenstore. When using indirection the

 * seg[] array doesn't contain specifications of the data buffers, but

 * references to scsiif_request_segment arrays, which in turn reference the

 * data buffers. While nr_segments holds the number of populated seg[] entries

 * (plus the set VSCSIIF_SG_GRANT bit), the number of scsiif_request_segment

 * elements referencing the target data buffers is calculated from the lengths

 * of the seg[] elements (the sum of all valid seg[].length divided by the

 * size of one scsiif_request_segment structure).

 */

#define VSCSIIF_ACT_SCSI_CDB		1

/*

 * Request abort of a running operation for the specified target given by

 * channel, id, lun and the operation's rqid in ref_rqid.

 */

#define VSCSIIF_ACT_SCSI_ABORT		2

/*

 * Request a device reset of the specified target (channel and id).

 */

#define VSCSIIF_ACT_SCSI_RESET		3

/*

 * Preset scatter/gather elements for a following request. Deprecated.

 * Keeping the define only to avoid usage of the value "4" for other actions.

 */

#define VSCSIIF_ACT_SCSI_SG_PRESET	4

/*

 * Maximum scatter/gather segments per request.

 *

 * Considering balance between allocating at least 16 "vscsiif_request"

 * structures on one page (4096 bytes) and the number of scatter/gather

 * elements needed, we decided to use 26 as a magic number.

 *

 * If "feature-sg-grant" is set, more scatter/gather elements can be specified

 * by placing them in one or more (up to VSCSIIF_SG_TABLESIZE) granted pages.

 * In this case the vscsiif_request seg elements don't contain references to

 * the user data, but to the SG elements referencing the user data.

 */

#define VSCSIIF_SG_TABLESIZE		26

/*

 * based on Linux kernel 2.6.18, still valid

 * Changing these values requires support of multiple protocols via the rings

 * as "old clients" will blindly use these values and the resulting structure

 * sizes.

 */

#define VSCSIIF_MAX_COMMAND_SIZE	16

#define VSCSIIF_SENSE_BUFFERSIZE	96

struct scsiif_request_segment {

	grant_ref_t gref;

	uint16_t offset;

	uint16_t length;

};

#define VSCSIIF_SG_PER_PAGE (PAGE_SIZE / sizeof(struct scsiif_request_segment))

/* Size of one request is 252 bytes */

struct vscsiif_request {

	uint16_t rqid;		/* private guest value, echoed in resp  */

	uint8_t act;		/* command between backend and frontend */

	uint8_t cmd_len;	/* valid CDB bytes */

	uint8_t cmnd[VSCSIIF_MAX_COMMAND_SIZE];	/* the CDB */

	uint16_t timeout_per_command;	/* deprecated */

	uint16_t channel, id, lun;	/* (virtual) device specification */

	uint16_t ref_rqid;		/* command abort reference */

	uint8_t sc_data_direction;	/* for DMA_TO_DEVICE(1)

					   DMA_FROM_DEVICE(2)

					   DMA_NONE(3) requests */

	uint8_t nr_segments;		/* Number of pieces of scatter-gather */

/*

 * flag in nr_segments: SG elements via grant page

 *

 * If VSCSIIF_SG_GRANT is set, the low 7 bits of nr_segments specify the number

 * of grant pages containing SG elements. Usable if "feature-sg-grant" set.

 */

#define VSCSIIF_SG_GRANT	0x80

	struct scsiif_request_segment seg[VSCSIIF_SG_TABLESIZE];

	uint32_t reserved[3];

};

/* Size of one response is 252 bytes */

struct vscsiif_response {

	uint16_t rqid;		/* identifies request */

	uint8_t padding;

	uint8_t sense_len;

	uint8_t sense_buffer[VSCSIIF_SENSE_BUFFERSIZE];

	int32_t rslt;

	uint32_t residual_len;	/* request bufflen -

				   return the value from physical device */

	uint32_t reserved[36];

};

DEFINE_RING_TYPES(vscsiif, struct vscsiif_request, struct vscsiif_response);

#endif /*__XEN__PUBLIC_IO_SCSI_H__*/