drivers/block/xen-blkback/common.h - maze/linux - Git at Google

 /*
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version 2
  * as published by the Free Software Foundation; or, when distributed
  * separately from the Linux kernel or incorporated into other
  * software packages, subject to the following license:
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this source file (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.
  */

 #ifndef __XEN_BLKIF__BACKEND__COMMON_H__
 #define __XEN_BLKIF__BACKEND__COMMON_H__

 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/vmalloc.h>
 #include <linux/wait.h>
 #include <linux/io.h>
 #include <linux/rbtree.h>
 #include <asm/setup.h>
 #include <asm/pgalloc.h>
 #include <asm/hypervisor.h>
 #include <xen/grant_table.h>
 #include <xen/xenbus.h>
 #include <xen/interface/io/ring.h>
 #include <xen/interface/io/blkif.h>
 #include <xen/interface/io/protocols.h>

 #define DRV_PFX "xen-blkback:"
 #define DPRINTK(fmt, args...)				\
 	pr_debug(DRV_PFX "(%s:%d) " fmt ".\n",		\
 		 __func__, __LINE__, ##args)


 /* Not a real protocol.  Used to generate ring structs which contain
  * the elements common to all protocols only.  This way we get a
  * compiler-checkable way to use common struct elements, so we can
  * avoid using switch(protocol) in a number of places.  */
 struct blkif_common_request {
 	char dummy;
 };
 struct blkif_common_response {
 	char dummy;
 };

 struct blkif_x86_32_request_rw {
 	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];
 } __attribute__((__packed__));

 struct blkif_x86_32_request_discard {
 	uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
 	blkif_vdev_t   _pad1;        /* was "handle" 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)  */
 	uint64_t       nr_sectors;
 } __attribute__((__packed__));

 struct blkif_x86_32_request_other {
 	uint8_t        _pad1;
 	blkif_vdev_t   _pad2;
 	uint64_t       id;           /* private guest value, echoed in resp  */
 } __attribute__((__packed__));

 struct blkif_x86_32_request {
 	uint8_t        operation;    /* BLKIF_OP_???                         */
 	union {
 		struct blkif_x86_32_request_rw rw;
 		struct blkif_x86_32_request_discard discard;
 		struct blkif_x86_32_request_other other;
 	} u;
 } __attribute__((__packed__));

 /* i386 protocol version */
 #pragma pack(push, 4)
 struct blkif_x86_32_response {
 	uint64_t        id;              /* copied from request */
 	uint8_t         operation;       /* copied from request */
 	int16_t         status;          /* BLKIF_RSP_???       */
 };
 #pragma pack(pop)
 /* x86_64 protocol version */

 struct blkif_x86_64_request_rw {
 	uint8_t        nr_segments;  /* number of segments                   */
 	blkif_vdev_t   handle;       /* only for read/write requests         */
 	uint32_t       _pad1;        /* offsetof(blkif_reqest..,u.rw.id)==8  */
 	uint64_t       id;
 	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 	struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 } __attribute__((__packed__));

 struct blkif_x86_64_request_discard {
 	uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
 	blkif_vdev_t   _pad1;        /* was "handle" for read/write requests */
         uint32_t       _pad2;        /* offsetof(blkif_..,u.discard.id)==8   */
 	uint64_t       id;
 	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 	uint64_t       nr_sectors;
 } __attribute__((__packed__));

 struct blkif_x86_64_request_other {
 	uint8_t        _pad1;
 	blkif_vdev_t   _pad2;
 	uint32_t       _pad3;        /* offsetof(blkif_..,u.discard.id)==8   */
 	uint64_t       id;           /* private guest value, echoed in resp  */
 } __attribute__((__packed__));

 struct blkif_x86_64_request {
 	uint8_t        operation;    /* BLKIF_OP_???                         */
 	union {
 		struct blkif_x86_64_request_rw rw;
 		struct blkif_x86_64_request_discard discard;
 		struct blkif_x86_64_request_other other;
 	} u;
 } __attribute__((__packed__));

 struct blkif_x86_64_response {
 	uint64_t       __attribute__((__aligned__(8))) id;
 	uint8_t         operation;       /* copied from request */
 	int16_t         status;          /* BLKIF_RSP_???       */
 };

 DEFINE_RING_TYPES(blkif_common, struct blkif_common_request,
 		  struct blkif_common_response);
 DEFINE_RING_TYPES(blkif_x86_32, struct blkif_x86_32_request,
 		  struct blkif_x86_32_response);
 DEFINE_RING_TYPES(blkif_x86_64, struct blkif_x86_64_request,
 		  struct blkif_x86_64_response);

 union blkif_back_rings {
 	struct blkif_back_ring        native;
 	struct blkif_common_back_ring common;
 	struct blkif_x86_32_back_ring x86_32;
 	struct blkif_x86_64_back_ring x86_64;
 };

 enum blkif_protocol {
 	BLKIF_PROTOCOL_NATIVE = 1,
 	BLKIF_PROTOCOL_X86_32 = 2,
 	BLKIF_PROTOCOL_X86_64 = 3,
 };

 struct xen_vbd {
 	/* What the domain refers to this vbd as. */
 	blkif_vdev_t		handle;
 	/* Non-zero -> read-only */
 	unsigned char		readonly;
 	/* VDISK_xxx */
 	unsigned char		type;
 	/* phys device that this vbd maps to. */
 	u32			pdevice;
 	struct block_device	*bdev;
 	/* Cached size parameter. */
 	sector_t		size;
 	unsigned int		flush_support:1;
 	unsigned int		discard_secure:1;
 	unsigned int		feature_gnt_persistent:1;
 	unsigned int		overflow_max_grants:1;
 };

 struct backend_info;


 struct persistent_gnt {
 	struct page *page;
 	grant_ref_t gnt;
 	grant_handle_t handle;
 	struct rb_node node;
 };

 struct xen_blkif {
 	/* Unique identifier for this interface. */
 	domid_t			domid;
 	unsigned int		handle;
 	/* Physical parameters of the comms window. */
 	unsigned int		irq;
 	/* Comms information. */
 	enum blkif_protocol	blk_protocol;
 	union blkif_back_rings	blk_rings;
 	void			*blk_ring;
 	/* The VBD attached to this interface. */
 	struct xen_vbd		vbd;
 	/* Back pointer to the backend_info. */
 	struct backend_info	*be;
 	/* Private fields. */
 	spinlock_t		blk_ring_lock;
 	atomic_t		refcnt;

 	wait_queue_head_t	wq;
 	/* for barrier (drain) requests */
 	struct completion	drain_complete;
 	atomic_t		drain;
 	/* One thread per one blkif. */
 	struct task_struct	*xenblkd;
 	unsigned int		waiting_reqs;

 	/* tree to store persistent grants */
 	struct rb_root		persistent_gnts;
 	unsigned int		persistent_gnt_c;

 	/* statistics */
 	unsigned long		st_print;
 	unsigned long long			st_rd_req;
 	unsigned long long			st_wr_req;
 	unsigned long long			st_oo_req;
 	unsigned long long			st_f_req;
 	unsigned long long			st_ds_req;
 	unsigned long long			st_rd_sect;
 	unsigned long long			st_wr_sect;

 	wait_queue_head_t	waiting_to_free;
 };


 #define vbd_sz(_v)	((_v)->bdev->bd_part ? \
 			 (_v)->bdev->bd_part->nr_sects : \
 			  get_capacity((_v)->bdev->bd_disk))

 #define xen_blkif_get(_b) (atomic_inc(&(_b)->refcnt))
 #define xen_blkif_put(_b)				\
 	do {						\
 		if (atomic_dec_and_test(&(_b)->refcnt))	\
 			wake_up(&(_b)->waiting_to_free);\
 	} while (0)

 struct phys_req {
 	unsigned short		dev;
 	blkif_sector_t		nr_sects;
 	struct block_device	*bdev;
 	blkif_sector_t		sector_number;
 };
 int xen_blkif_interface_init(void);

 int xen_blkif_xenbus_init(void);

 irqreturn_t xen_blkif_be_int(int irq, void *dev_id);
 int xen_blkif_schedule(void *arg);

 int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
 			      struct backend_info *be, int state);

 int xen_blkbk_barrier(struct xenbus_transaction xbt,
 		      struct backend_info *be, int state);
 struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be);

 static inline void blkif_get_x86_32_req(struct blkif_request *dst,
 					struct blkif_x86_32_request *src)
 {
 	int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
 	dst->operation = src->operation;
 	switch (src->operation) {
 	case BLKIF_OP_READ:
 	case BLKIF_OP_WRITE:
 	case BLKIF_OP_WRITE_BARRIER:
 	case BLKIF_OP_FLUSH_DISKCACHE:
 		dst->u.rw.nr_segments = src->u.rw.nr_segments;
 		dst->u.rw.handle = src->u.rw.handle;
 		dst->u.rw.id = src->u.rw.id;
 		dst->u.rw.sector_number = src->u.rw.sector_number;
 		barrier();
 		if (n > dst->u.rw.nr_segments)
 			n = dst->u.rw.nr_segments;
 		for (i = 0; i < n; i++)
 			dst->u.rw.seg[i] = src->u.rw.seg[i];
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
 		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
 	default:
 		/*
 		 * Don't know how to translate this op. Only get the
 		 * ID so failure can be reported to the frontend.
 		 */
 		dst->u.other.id = src->u.other.id;
 		break;
 	}
 }

 static inline void blkif_get_x86_64_req(struct blkif_request *dst,
 					struct blkif_x86_64_request *src)
 {
 	int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
 	dst->operation = src->operation;
 	switch (src->operation) {
 	case BLKIF_OP_READ:
 	case BLKIF_OP_WRITE:
 	case BLKIF_OP_WRITE_BARRIER:
 	case BLKIF_OP_FLUSH_DISKCACHE:
 		dst->u.rw.nr_segments = src->u.rw.nr_segments;
 		dst->u.rw.handle = src->u.rw.handle;
 		dst->u.rw.id = src->u.rw.id;
 		dst->u.rw.sector_number = src->u.rw.sector_number;
 		barrier();
 		if (n > dst->u.rw.nr_segments)
 			n = dst->u.rw.nr_segments;
 		for (i = 0; i < n; i++)
 			dst->u.rw.seg[i] = src->u.rw.seg[i];
 		break;
 	case BLKIF_OP_DISCARD:
 		dst->u.discard.flag = src->u.discard.flag;
 		dst->u.discard.id = src->u.discard.id;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
 	default:
 		/*
 		 * Don't know how to translate this op. Only get the
 		 * ID so failure can be reported to the frontend.
 		 */
 		dst->u.other.id = src->u.other.id;
 		break;
 	}
 }

 #endif /* __XEN_BLKIF__BACKEND__COMMON_H__ */
	/*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License version 2
	* as published by the Free Software Foundation; or, when distributed
	* separately from the Linux kernel or incorporated into other
	* software packages, subject to the following license:
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this source file (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.
	*/

	#ifndef __XEN_BLKIF__BACKEND__COMMON_H__
	#define __XEN_BLKIF__BACKEND__COMMON_H__

	#include <linux/module.h>
	#include <linux/interrupt.h>
	#include <linux/slab.h>
	#include <linux/blkdev.h>
	#include <linux/vmalloc.h>
	#include <linux/wait.h>
	#include <linux/io.h>
	#include <linux/rbtree.h>
	#include <asm/setup.h>
	#include <asm/pgalloc.h>
	#include <asm/hypervisor.h>
	#include <xen/grant_table.h>
	#include <xen/xenbus.h>
	#include <xen/interface/io/ring.h>
	#include <xen/interface/io/blkif.h>
	#include <xen/interface/io/protocols.h>

	#define DRV_PFX "xen-blkback:"
	#define DPRINTK(fmt, args...) \
	pr_debug(DRV_PFX "(%s:%d) " fmt ".\n", \
	__func__, __LINE__, ##args)


	/* Not a real protocol. Used to generate ring structs which contain
	* the elements common to all protocols only. This way we get a
	* compiler-checkable way to use common struct elements, so we can
	* avoid using switch(protocol) in a number of places. */
	struct blkif_common_request {
	char dummy;
	};
	struct blkif_common_response {
	char dummy;
	};

	struct blkif_x86_32_request_rw {
	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];
	} __attribute__((__packed__));

	struct blkif_x86_32_request_discard {
	uint8_t flag; /* BLKIF_DISCARD_SECURE or zero */
	blkif_vdev_t _pad1; /* was "handle" 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) */
	uint64_t nr_sectors;
	} __attribute__((__packed__));

	struct blkif_x86_32_request_other {
	uint8_t _pad1;
	blkif_vdev_t _pad2;
	uint64_t id; /* private guest value, echoed in resp */
	} __attribute__((__packed__));

	struct blkif_x86_32_request {
	uint8_t operation; /* BLKIF_OP_??? */
	union {
	struct blkif_x86_32_request_rw rw;
	struct blkif_x86_32_request_discard discard;
	struct blkif_x86_32_request_other other;
	} u;
	} __attribute__((__packed__));

	/* i386 protocol version */
	#pragma pack(push, 4)
	struct blkif_x86_32_response {
	uint64_t id; /* copied from request */
	uint8_t operation; /* copied from request */
	int16_t status; /* BLKIF_RSP_??? */
	};
	#pragma pack(pop)
	/* x86_64 protocol version */

	struct blkif_x86_64_request_rw {
	uint8_t nr_segments; /* number of segments */
	blkif_vdev_t handle; /* only for read/write requests */
	uint32_t _pad1; /* offsetof(blkif_reqest..,u.rw.id)==8 */
	uint64_t id;
	blkif_sector_t sector_number;/* start sector idx on disk (r/w only) */
	struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
	} __attribute__((__packed__));

	struct blkif_x86_64_request_discard {
	uint8_t flag; /* BLKIF_DISCARD_SECURE or zero */
	blkif_vdev_t _pad1; /* was "handle" for read/write requests */
	uint32_t _pad2; /* offsetof(blkif_..,u.discard.id)==8 */
	uint64_t id;
	blkif_sector_t sector_number;/* start sector idx on disk (r/w only) */
	uint64_t nr_sectors;
	} __attribute__((__packed__));

	struct blkif_x86_64_request_other {
	uint8_t _pad1;
	blkif_vdev_t _pad2;
	uint32_t _pad3; /* offsetof(blkif_..,u.discard.id)==8 */
	uint64_t id; /* private guest value, echoed in resp */
	} __attribute__((__packed__));

	struct blkif_x86_64_request {
	uint8_t operation; /* BLKIF_OP_??? */
	union {
	struct blkif_x86_64_request_rw rw;
	struct blkif_x86_64_request_discard discard;
	struct blkif_x86_64_request_other other;
	} u;
	} __attribute__((__packed__));

	struct blkif_x86_64_response {
	uint64_t __attribute__((__aligned__(8))) id;
	uint8_t operation; /* copied from request */
	int16_t status; /* BLKIF_RSP_??? */
	};

	DEFINE_RING_TYPES(blkif_common, struct blkif_common_request,
	struct blkif_common_response);
	DEFINE_RING_TYPES(blkif_x86_32, struct blkif_x86_32_request,
	struct blkif_x86_32_response);
	DEFINE_RING_TYPES(blkif_x86_64, struct blkif_x86_64_request,
	struct blkif_x86_64_response);

	union blkif_back_rings {
	struct blkif_back_ring native;
	struct blkif_common_back_ring common;
	struct blkif_x86_32_back_ring x86_32;
	struct blkif_x86_64_back_ring x86_64;
	};

	enum blkif_protocol {
	BLKIF_PROTOCOL_NATIVE = 1,
	BLKIF_PROTOCOL_X86_32 = 2,
	BLKIF_PROTOCOL_X86_64 = 3,
	};

	struct xen_vbd {
	/* What the domain refers to this vbd as. */
	blkif_vdev_t handle;
	/* Non-zero -> read-only */
	unsigned char readonly;
	/* VDISK_xxx */
	unsigned char type;
	/* phys device that this vbd maps to. */
	u32 pdevice;
	struct block_device *bdev;
	/* Cached size parameter. */
	sector_t size;
	unsigned int flush_support:1;
	unsigned int discard_secure:1;
	unsigned int feature_gnt_persistent:1;
	unsigned int overflow_max_grants:1;
	};

	struct backend_info;


	struct persistent_gnt {
	struct page *page;
	grant_ref_t gnt;
	grant_handle_t handle;
	struct rb_node node;
	};

	struct xen_blkif {
	/* Unique identifier for this interface. */
	domid_t domid;
	unsigned int handle;
	/* Physical parameters of the comms window. */
	unsigned int irq;
	/* Comms information. */
	enum blkif_protocol blk_protocol;
	union blkif_back_rings blk_rings;
	void *blk_ring;
	/* The VBD attached to this interface. */
	struct xen_vbd vbd;
	/* Back pointer to the backend_info. */
	struct backend_info *be;
	/* Private fields. */
	spinlock_t blk_ring_lock;
	atomic_t refcnt;

	wait_queue_head_t wq;
	/* for barrier (drain) requests */
	struct completion drain_complete;
	atomic_t drain;
	/* One thread per one blkif. */
	struct task_struct *xenblkd;
	unsigned int waiting_reqs;

	/* tree to store persistent grants */
	struct rb_root persistent_gnts;
	unsigned int persistent_gnt_c;

	/* statistics */
	unsigned long st_print;
	unsigned long long st_rd_req;
	unsigned long long st_wr_req;
	unsigned long long st_oo_req;
	unsigned long long st_f_req;
	unsigned long long st_ds_req;
	unsigned long long st_rd_sect;
	unsigned long long st_wr_sect;

	wait_queue_head_t waiting_to_free;
	};


	#define vbd_sz(_v) ((_v)->bdev->bd_part ? \
	(_v)->bdev->bd_part->nr_sects : \
	get_capacity((_v)->bdev->bd_disk))

	#define xen_blkif_get(_b) (atomic_inc(&(_b)->refcnt))
	#define xen_blkif_put(_b) \
	do { \
	if (atomic_dec_and_test(&(_b)->refcnt)) \
	wake_up(&(_b)->waiting_to_free);\
	} while (0)

	struct phys_req {
	unsigned short dev;
	blkif_sector_t nr_sects;
	struct block_device *bdev;
	blkif_sector_t sector_number;
	};
	int xen_blkif_interface_init(void);

	int xen_blkif_xenbus_init(void);

	irqreturn_t xen_blkif_be_int(int irq, void *dev_id);
	int xen_blkif_schedule(void *arg);

	int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
	struct backend_info *be, int state);

	int xen_blkbk_barrier(struct xenbus_transaction xbt,
	struct backend_info *be, int state);
	struct xenbus_device xen_blkbk_xenbus(struct backend_info be);

	static inline void blkif_get_x86_32_req(struct blkif_request *dst,
	struct blkif_x86_32_request *src)
	{
	int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
	dst->operation = src->operation;
	switch (src->operation) {
	case BLKIF_OP_READ:
	case BLKIF_OP_WRITE:
	case BLKIF_OP_WRITE_BARRIER:
	case BLKIF_OP_FLUSH_DISKCACHE:
	dst->u.rw.nr_segments = src->u.rw.nr_segments;
	dst->u.rw.handle = src->u.rw.handle;
	dst->u.rw.id = src->u.rw.id;
	dst->u.rw.sector_number = src->u.rw.sector_number;
	barrier();
	if (n > dst->u.rw.nr_segments)
	n = dst->u.rw.nr_segments;
	for (i = 0; i < n; i++)
	dst->u.rw.seg[i] = src->u.rw.seg[i];
	break;
	case BLKIF_OP_DISCARD:
	dst->u.discard.flag = src->u.discard.flag;
	dst->u.discard.id = src->u.discard.id;
	dst->u.discard.sector_number = src->u.discard.sector_number;
	dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
	break;
	default:
	/*
	* Don't know how to translate this op. Only get the
	* ID so failure can be reported to the frontend.
	*/
	dst->u.other.id = src->u.other.id;
	break;
	}
	}

	static inline void blkif_get_x86_64_req(struct blkif_request *dst,
	struct blkif_x86_64_request *src)
	{
	int i, n = BLKIF_MAX_SEGMENTS_PER_REQUEST;
	dst->operation = src->operation;
	switch (src->operation) {
	case BLKIF_OP_READ:
	case BLKIF_OP_WRITE:
	case BLKIF_OP_WRITE_BARRIER:
	case BLKIF_OP_FLUSH_DISKCACHE:
	dst->u.rw.nr_segments = src->u.rw.nr_segments;
	dst->u.rw.handle = src->u.rw.handle;
	dst->u.rw.id = src->u.rw.id;
	dst->u.rw.sector_number = src->u.rw.sector_number;
	barrier();
	if (n > dst->u.rw.nr_segments)
	n = dst->u.rw.nr_segments;
	for (i = 0; i < n; i++)
	dst->u.rw.seg[i] = src->u.rw.seg[i];
	break;
	case BLKIF_OP_DISCARD:
	dst->u.discard.flag = src->u.discard.flag;
	dst->u.discard.id = src->u.discard.id;
	dst->u.discard.sector_number = src->u.discard.sector_number;
	dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
	break;
	default:
	/*
	* Don't know how to translate this op. Only get the
	* ID so failure can be reported to the frontend.
	*/
	dst->u.other.id = src->u.other.id;
	break;
	}
	}

	#endif /* __XEN_BLKIF__BACKEND__COMMON_H__ */