/* SPDX-License-Identifier: GPL-2.0 OR MIT */

/*
 * Xen frontend/backend page directory based shared buffer
 * helper module.
 *
 * Copyright (C) 2018 EPAM Systems Inc.
 *
 * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
 */

#ifndef __XEN_FRONT_PGDIR_SHBUF_H_
#define __XEN_FRONT_PGDIR_SHBUF_H_

#include <linux/kernel.h>

#include <xen/grant_table.h>

struct xen_front_pgdir_shbuf_ops;

struct xen_front_pgdir_shbuf {
        /*
         * Number of references granted for the backend use:
         *
         *  - for frontend allocated/imported buffers this holds the number
         *    of grant references for the page directory and the pages
         *    of the buffer
         *
         *  - for the buffer provided by the backend this only holds the number
         *    of grant references for the page directory itself as grant
         *    references for the buffer will be provided by the backend.
         */
        int num_grefs;
        grant_ref_t *grefs;
        /* Page directory backing storage. */
        u8 *directory;

        /*
         * Number of pages for the shared buffer itself (excluding the page
         * directory).
         */
        int num_pages;
        /*
         * Backing storage of the shared buffer: these are the pages being
         * shared.
         */
        struct page **pages;

        struct xenbus_device *xb_dev;

        /* These are the ops used internally depending on be_alloc mode. */
        const struct xen_front_pgdir_shbuf_ops *ops;

        /* Xen map handles for the buffer allocated by the backend. */
        grant_handle_t *backend_map_handles;
};

struct xen_front_pgdir_shbuf_cfg {
        struct xenbus_device *xb_dev;

        /* Number of pages of the buffer backing storage. */
        int num_pages;
        /* Pages of the buffer to be shared. */
        struct page **pages;

        /*
         * This is allocated outside because there are use-cases when
         * the buffer structure is allocated as a part of a bigger one.
         */
        struct xen_front_pgdir_shbuf *pgdir;
        /*
         * Mode of grant reference sharing: if set then backend will share
         * grant references to the buffer with the frontend.
         */
        int be_alloc;
};

int xen_front_pgdir_shbuf_alloc(struct xen_front_pgdir_shbuf_cfg *cfg);

grant_ref_t
xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf);

int xen_front_pgdir_shbuf_map(struct xen_front_pgdir_shbuf *buf);

int xen_front_pgdir_shbuf_unmap(struct xen_front_pgdir_shbuf *buf);

void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf);

#endif /* __XEN_FRONT_PGDIR_SHBUF_H_ */