include/xen/interface/io/ring.h

Source file repositories/reference/linux-study-clean/include/xen/interface/io/ring.h

File Facts

System
Linux kernel
Corpus path
include/xen/interface/io/ring.h
Extension
.h
Size
23066 bytes
Lines
448
Domain
Repository Root And Misc
Bucket
include
Inferred role
Repository Root And Misc: implementation source
Status
source implementation candidate

Why This File Exists

Top-level or miscellaneous repository surface. Use this as map coverage unless a later manual pass promotes the file into a deeper subsystem dossier.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef __XEN_PUBLIC_IO_RING_H__
#define __XEN_PUBLIC_IO_RING_H__

/*
 * When #include'ing this header, you need to provide the following
 * declaration upfront:
 * - standard integers types (uint8_t, uint16_t, etc)
 * They are provided by stdint.h of the standard headers.
 *
 * In addition, if you intend to use the FLEX macros, you also need to
 * provide the following, before invoking the FLEX macros:
 * - size_t
 * - memcpy
 * - grant_ref_t
 * These declarations are provided by string.h of the standard headers,
 * and grant_table.h from the Xen public headers.
 */

#include <xen/interface/grant_table.h>

typedef unsigned int RING_IDX;

/* Round a 32-bit unsigned constant down to the nearest power of two. */
#define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
#define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
#define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))

/*
 * Calculate size of a shared ring, given the total available space for the
 * ring and indexes (_sz), and the name tag of the request/response structure.
 * A ring contains as many entries as will fit, rounded down to the nearest
 * power of two (so we can mask with (size-1) to loop around).
 */
#define __CONST_RING_SIZE(_s, _sz) \
    (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
	    sizeof(((struct _s##_sring *)0)->ring[0])))
/*
 * The same for passing in an actual pointer instead of a name tag.
 */
#define __RING_SIZE(_s, _sz) \
    (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))

/*
 * Macros to make the correct C datatypes for a new kind of ring.
 *
 * To make a new ring datatype, you need to have two message structures,
 * let's say request_t, and response_t already defined.
 *
 * In a header where you want the ring datatype declared, you then do:
 *
 *     DEFINE_RING_TYPES(mytag, request_t, response_t);
 *
 * These expand out to give you a set of types, as you can see below.
 * The most important of these are:
 *
 *     mytag_sring_t      - The shared ring.
 *     mytag_front_ring_t - The 'front' half of the ring.
 *     mytag_back_ring_t  - The 'back' half of the ring.
 *
 * To initialize a ring in your code you need to know the location and size
 * of the shared memory area (PAGE_SIZE, for instance). To initialise
 * the front half:
 *
 *     mytag_front_ring_t ring;
 *     XEN_FRONT_RING_INIT(&ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
 *
 * Initializing the back follows similarly (note that only the front
 * initializes the shared ring):
 *
 *     mytag_back_ring_t back_ring;
 *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
 */

#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
                                                                        \
/* Shared ring entry */                                                 \
union __name##_sring_entry {                                            \
    __req_t req;                                                        \
    __rsp_t rsp;                                                        \
};                                                                      \
                                                                        \
/* Shared ring page */                                                  \
struct __name##_sring {                                                 \
    RING_IDX req_prod, req_event;                                       \
    RING_IDX rsp_prod, rsp_event;                                       \
    uint8_t __pad[48];                                                  \
    union __name##_sring_entry ring[];                                  \
};                                                                      \

Annotation

Implementation Notes