/******************************************************************************
 *
 * Back-end of the driver for virtual block devices. This portion of the
 * driver exports a 'unified' block-device interface that can be accessed
 * by any operating system that implements a compatible front end. A
 * reference front-end implementation can be found in:
 *  drivers/block/xen-blkfront.c
 *
 * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
 * Copyright (c) 2005, Christopher Clark
 *
 * 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.
 */

#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/delay.h>
#include <linux/freezer.h>
#include <linux/bitmap.h>

#include <xen/events.h>
#include <xen/page.h>
#include <xen/xen.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>
#include <xen/balloon.h>
#include "common.h"

/*
 * These are rather arbitrary. They are fairly large because adjacent requests
 * pulled from a communication ring are quite likely to end up being part of
 * the same scatter/gather request at the disc.
 *
 * ** TRY INCREASING 'xen_blkif_reqs' IF WRITE SPEEDS SEEM TOO LOW **
 *
 * This will increase the chances of being able to write whole tracks.
 * 64 should be enough to keep us competitive with Linux.
 */
static int xen_blkif_reqs = 64;
module_param_named(reqs, xen_blkif_reqs, int, 0);
MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");

/* Run-time switchable: /sys/module/blkback/parameters/ */
static unsigned int log_stats;
module_param(log_stats, int, 0644);

/*
 * Each outstanding request that we've passed to the lower device layers has a
 * 'pending_req' allocated to it. Each buffer_head that completes decrements
 * the pendcnt towards zero. When it hits zero, the specified domain has a
 * response queued for it, with the saved 'id' passed back.
 */
struct pending_req {
        struct xen_blkif        *blkif;
        u64                     id;
        int                     nr_pages;
        atomic_t                pendcnt;
        unsigned short          operation;
        int                     status;
        struct list_head        free_list;
        DECLARE_BITMAP(unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
};

#define BLKBACK_INVALID_HANDLE (~0)

struct xen_blkbk {
        struct pending_req      *pending_reqs;
        /* List of all 'pending_req' available */
        struct list_head        pending_free;
        /* And its spinlock. */
        spinlock_t              pending_free_lock;
        wait_queue_head_t       pending_free_wq;
        /* The list of all pages that are available. */
        struct page             **pending_pages;
        /* And the grant handles that are available. */
        grant_handle_t          *pending_grant_handles;
};

static struct xen_blkbk *blkbk;

/*
 * Maximum number of grant pages that can be mapped in blkback.
 * BLKIF_MAX_SEGMENTS_PER_REQUEST * RING_SIZE is the maximum number of
 * pages that blkback will persistently map.
 * Currently, this is:
 * RING_SIZE = 32 (for all known ring types)
 * BLKIF_MAX_SEGMENTS_PER_REQUEST = 11
 * sizeof(struct persistent_gnt) = 48
 * So the maximum memory used to store the grants is:
 * 32 * 11 * 48 = 16896 bytes
 */
static inline unsigned int max_mapped_grant_pages(enum blkif_protocol protocol)
{
        switch (protocol) {
        case BLKIF_PROTOCOL_NATIVE:
                return __CONST_RING_SIZE(blkif, PAGE_SIZE) *
                           BLKIF_MAX_SEGMENTS_PER_REQUEST;
        case BLKIF_PROTOCOL_X86_32:
                return __CONST_RING_SIZE(blkif_x86_32, PAGE_SIZE) *
                           BLKIF_MAX_SEGMENTS_PER_REQUEST;
        case BLKIF_PROTOCOL_X86_64:
                return __CONST_RING_SIZE(blkif_x86_64, PAGE_SIZE) *
                           BLKIF_MAX_SEGMENTS_PER_REQUEST;
        default:
                BUG();
        }
        return 0;
}


/*
 * Little helpful macro to figure out the index and virtual address of the
 * pending_pages[..]. For each 'pending_req' we have have up to
 * BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
 * 10 and would index in the pending_pages[..].
 */
static inline int vaddr_pagenr(struct pending_req *req, int seg)
{
        return (req - blkbk->pending_reqs) *
                BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
}

#define pending_page(req, seg) pending_pages[vaddr_pagenr(req, seg)]

static inline unsigned long vaddr(struct pending_req *req, int seg)
{
        unsigned long pfn = page_to_pfn(blkbk->pending_page(req, seg));
        return (unsigned long)pfn_to_kaddr(pfn);
}

#define pending_handle(_req, _seg) \
        (blkbk->pending_grant_handles[vaddr_pagenr(_req, _seg)])


static int do_block_io_op(struct xen_blkif *blkif);
static int dispatch_rw_block_io(struct xen_blkif *blkif,
                                struct blkif_request *req,
                                struct pending_req *pending_req);
static void make_response(struct xen_blkif *blkif, u64 id,
                          unsigned short op, int st);

#define foreach_grant_safe(pos, n, rbtree, node) \
        for ((pos) = container_of(rb_first((rbtree)), typeof(*(pos)), node), \
             (n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL; \
             &(pos)->node != NULL; \
             (pos) = container_of(n, typeof(*(pos)), node), \
             (n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL)


static void add_persistent_gnt(struct rb_root *root,
                               struct persistent_gnt *persistent_gnt)
{
        struct rb_node **new = &(root->rb_node), *parent = NULL;
        struct persistent_gnt *this;

        /* Figure out where to put new node */
        while (*new) {
                this = container_of(*new, struct persistent_gnt, node);

                parent = *new;
                if (persistent_gnt->gnt < this->gnt)
                        new = &((*new)->rb_left);
                else if (persistent_gnt->gnt > this->gnt)
                        new = &((*new)->rb_right);
                else {
                        pr_alert(DRV_PFX " trying to add a gref that's already in the tree\n");
                        BUG();
                }
        }

        /* Add new node and rebalance tree. */
        rb_link_node(&(persistent_gnt->node), parent, new);
        rb_insert_color(&(persistent_gnt->node), root);
}

static struct persistent_gnt *get_persistent_gnt(struct rb_root *root,
                                                 grant_ref_t gref)
{
        struct persistent_gnt *data;
        struct rb_node *node = root->rb_node;

        while (node) {
                data = container_of(node, struct persistent_gnt, node);

                if (gref < data->gnt)
                        node = node->rb_left;
                else if (gref > data->gnt)
                        node = node->rb_right;
                else
                        return data;
        }
        return NULL;
}

static void free_persistent_gnts(struct rb_root *root, unsigned int num)
{
        struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct persistent_gnt *persistent_gnt;
        struct rb_node *n;
        int ret = 0;
        int segs_to_unmap = 0;

        foreach_grant_safe(persistent_gnt, n, root, node) {
                BUG_ON(persistent_gnt->handle ==
                        BLKBACK_INVALID_HANDLE);
                gnttab_set_unmap_op(&unmap[segs_to_unmap],
                        (unsigned long) pfn_to_kaddr(page_to_pfn(
                                persistent_gnt->page)),
                        GNTMAP_host_map,
                        persistent_gnt->handle);

                pages[segs_to_unmap] = persistent_gnt->page;

                if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST ||
                        !rb_next(&persistent_gnt->node)) {
                        ret = gnttab_unmap_refs(unmap, NULL, pages,
                                segs_to_unmap);
                        BUG_ON(ret);
                        free_xenballooned_pages(segs_to_unmap, pages);
                        segs_to_unmap = 0;
                }

                rb_erase(&persistent_gnt->node, root);
                kfree(persistent_gnt);
                num--;
        }
        BUG_ON(num != 0);
}

/*
 * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
 */
static struct pending_req *alloc_req(void)
{
        struct pending_req *req = NULL;
        unsigned long flags;

        spin_lock_irqsave(&blkbk->pending_free_lock, flags);
        if (!list_empty(&blkbk->pending_free)) {
                req = list_entry(blkbk->pending_free.next, struct pending_req,
                                 free_list);
                list_del(&req->free_list);
        }
        spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
        return req;
}

/*
 * Return the 'pending_req' structure back to the freepool. We also
 * wake up the thread if it was waiting for a free page.
 */
static void free_req(struct pending_req *req)
{
        unsigned long flags;
        int was_empty;

        spin_lock_irqsave(&blkbk->pending_free_lock, flags);
        was_empty = list_empty(&blkbk->pending_free);
        list_add(&req->free_list, &blkbk->pending_free);
        spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
        if (was_empty)
                wake_up(&blkbk->pending_free_wq);
}

/*
 * Routines for managing virtual block devices (vbds).
 */
static int xen_vbd_translate(struct phys_req *req, struct xen_blkif *blkif,
                             int operation)
{
        struct xen_vbd *vbd = &blkif->vbd;
        int rc = -EACCES;

        if ((operation != READ) && vbd->readonly)
                goto out;

        if (likely(req->nr_sects)) {
                blkif_sector_t end = req->sector_number + req->nr_sects;

                if (unlikely(end < req->sector_number))
                        goto out;
                if (unlikely(end > vbd_sz(vbd)))
                        goto out;
        }

        req->dev  = vbd->pdevice;
        req->bdev = vbd->bdev;
        rc = 0;

 out:
        return rc;
}

static void xen_vbd_resize(struct xen_blkif *blkif)
{
        struct xen_vbd *vbd = &blkif->vbd;
        struct xenbus_transaction xbt;
        int err;
        struct xenbus_device *dev = xen_blkbk_xenbus(blkif->be);
        unsigned long long new_size = vbd_sz(vbd);

        pr_info(DRV_PFX "VBD Resize: Domid: %d, Device: (%d, %d)\n",
                blkif->domid, MAJOR(vbd->pdevice), MINOR(vbd->pdevice));
        pr_info(DRV_PFX "VBD Resize: new size %llu\n", new_size);
        vbd->size = new_size;
again:
        err = xenbus_transaction_start(&xbt);
        if (err) {
                pr_warn(DRV_PFX "Error starting transaction");
                return;
        }
        err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
                            (unsigned long long)vbd_sz(vbd));
        if (err) {
                pr_warn(DRV_PFX "Error writing new size");
                goto abort;
        }
        /*
         * Write the current state; we will use this to synchronize
         * the front-end. If the current state is "connected" the
         * front-end will get the new size information online.
         */
        err = xenbus_printf(xbt, dev->nodename, "state", "%d", dev->state);
        if (err) {
                pr_warn(DRV_PFX "Error writing the state");
                goto abort;
        }

        err = xenbus_transaction_end(xbt, 0);
        if (err == -EAGAIN)
                goto again;
        if (err)
                pr_warn(DRV_PFX "Error ending transaction");
        return;
abort:
        xenbus_transaction_end(xbt, 1);
}

/*
 * Notification from the guest OS.
 */
static void blkif_notify_work(struct xen_blkif *blkif)
{
        blkif->waiting_reqs = 1;
        wake_up(&blkif->wq);
}

irqreturn_t xen_blkif_be_int(int irq, void *dev_id)
{
        blkif_notify_work(dev_id);
        return IRQ_HANDLED;
}

/*
 * SCHEDULER FUNCTIONS
 */

static void print_stats(struct xen_blkif *blkif)
{
        pr_info("xen-blkback (%s): oo %3llu  |  rd %4llu  |  wr %4llu  |  f %4llu"
                 "  |  ds %4llu\n",
                 current->comm, blkif->st_oo_req,
                 blkif->st_rd_req, blkif->st_wr_req,
                 blkif->st_f_req, blkif->st_ds_req);
        blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
        blkif->st_rd_req = 0;
        blkif->st_wr_req = 0;
        blkif->st_oo_req = 0;
        blkif->st_ds_req = 0;
}

int xen_blkif_schedule(void *arg)
{
        struct xen_blkif *blkif = arg;
        struct xen_vbd *vbd = &blkif->vbd;

        xen_blkif_get(blkif);

        while (!kthread_should_stop()) {
                if (try_to_freeze())
                        continue;
                if (unlikely(vbd->size != vbd_sz(vbd)))
                        xen_vbd_resize(blkif);

                wait_event_interruptible(
                        blkif->wq,
                        blkif->waiting_reqs || kthread_should_stop());
                wait_event_interruptible(
                        blkbk->pending_free_wq,
                        !list_empty(&blkbk->pending_free) ||
                        kthread_should_stop());

                blkif->waiting_reqs = 0;
                smp_mb(); /* clear flag *before* checking for work */

                if (do_block_io_op(blkif))
                        blkif->waiting_reqs = 1;

                if (log_stats && time_after(jiffies, blkif->st_print))
                        print_stats(blkif);
        }

        /* Free all persistent grant pages */
        if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
                free_persistent_gnts(&blkif->persistent_gnts,
                        blkif->persistent_gnt_c);

        BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
        blkif->persistent_gnt_c = 0;

        if (log_stats)
                print_stats(blkif);

        blkif->xenblkd = NULL;
        xen_blkif_put(blkif);

        return 0;
}

struct seg_buf {
        unsigned int offset;
        unsigned int nsec;
};
/*
 * Unmap the grant references, and also remove the M2P over-rides
 * used in the 'pending_req'.
 */
static void xen_blkbk_unmap(struct pending_req *req)
{
        struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        unsigned int i, invcount = 0;
        grant_handle_t handle;
        int ret;

        for (i = 0; i < req->nr_pages; i++) {
                if (!test_bit(i, req->unmap_seg))
                        continue;
                handle = pending_handle(req, i);
                if (handle == BLKBACK_INVALID_HANDLE)
                        continue;
                gnttab_set_unmap_op(&unmap[invcount], vaddr(req, i),
                                    GNTMAP_host_map, handle);
                pending_handle(req, i) = BLKBACK_INVALID_HANDLE;
                pages[invcount] = virt_to_page(vaddr(req, i));
                invcount++;
        }

        ret = gnttab_unmap_refs(unmap, NULL, pages, invcount);
        BUG_ON(ret);
}

static int xen_blkbk_map(struct blkif_request *req,
                         struct pending_req *pending_req,
                         struct seg_buf seg[],
                         struct page *pages[])
{
        struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct persistent_gnt *persistent_gnt = NULL;
        struct xen_blkif *blkif = pending_req->blkif;
        phys_addr_t addr = 0;
        int i, j;
        bool new_map;
        int nseg = req->u.rw.nr_segments;
        int segs_to_map = 0;
        int ret = 0;
        int use_persistent_gnts;

        use_persistent_gnts = (blkif->vbd.feature_gnt_persistent);

        BUG_ON(blkif->persistent_gnt_c >
                   max_mapped_grant_pages(pending_req->blkif->blk_protocol));

        /*
         * Fill out preq.nr_sects with proper amount of sectors, and setup
         * assign map[..] with the PFN of the page in our domain with the
         * corresponding grant reference for each page.
         */
        for (i = 0; i < nseg; i++) {
                uint32_t flags;

                if (use_persistent_gnts)
                        persistent_gnt = get_persistent_gnt(
                                &blkif->persistent_gnts,
                                req->u.rw.seg[i].gref);

                if (persistent_gnt) {
                        /*
                         * We are using persistent grants and
                         * the grant is already mapped
                         */
                        new_map = false;
                } else if (use_persistent_gnts &&
                           blkif->persistent_gnt_c <
                           max_mapped_grant_pages(blkif->blk_protocol)) {
                        /*
                         * We are using persistent grants, the grant is
                         * not mapped but we have room for it
                         */
                        new_map = true;
                        persistent_gnt = kmalloc(
                                sizeof(struct persistent_gnt),
                                GFP_KERNEL);
                        if (!persistent_gnt)
                                return -ENOMEM;
                        if (alloc_xenballooned_pages(1, &persistent_gnt->page,
                            false)) {
                                kfree(persistent_gnt);
                                return -ENOMEM;
                        }
                        persistent_gnt->gnt = req->u.rw.seg[i].gref;
                        persistent_gnt->handle = BLKBACK_INVALID_HANDLE;

                        pages_to_gnt[segs_to_map] =
                                persistent_gnt->page;
                        addr = (unsigned long) pfn_to_kaddr(
                                page_to_pfn(persistent_gnt->page));

                        add_persistent_gnt(&blkif->persistent_gnts,
                                persistent_gnt);
                        blkif->persistent_gnt_c++;
                        pr_debug(DRV_PFX " grant %u added to the tree of persistent grants, using %u/%u\n",
                                 persistent_gnt->gnt, blkif->persistent_gnt_c,
                                 max_mapped_grant_pages(blkif->blk_protocol));
                } else {
                        /*
                         * We are either using persistent grants and
                         * hit the maximum limit of grants mapped,
                         * or we are not using persistent grants.
                         */
                        if (use_persistent_gnts &&
                                !blkif->vbd.overflow_max_grants) {
                                blkif->vbd.overflow_max_grants = 1;
                                pr_alert(DRV_PFX " domain %u, device %#x is using maximum number of persistent grants\n",
                                         blkif->domid, blkif->vbd.handle);
                        }
                        new_map = true;
                        pages[i] = blkbk->pending_page(pending_req, i);
                        addr = vaddr(pending_req, i);
                        pages_to_gnt[segs_to_map] =
                                blkbk->pending_page(pending_req, i);
                }

                if (persistent_gnt) {
                        pages[i] = persistent_gnt->page;
                        persistent_gnts[i] = persistent_gnt;
                } else {
                        persistent_gnts[i] = NULL;
                }

                if (new_map) {
                        flags = GNTMAP_host_map;
                        if (!persistent_gnt &&
                            (pending_req->operation != BLKIF_OP_READ))
                                flags |= GNTMAP_readonly;
                        gnttab_set_map_op(&map[segs_to_map++], addr,
                                          flags, req->u.rw.seg[i].gref,
                                          blkif->domid);
                }
        }

        if (segs_to_map) {
                ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
                BUG_ON(ret);
        }

        /*
         * Now swizzle the MFN in our domain with the MFN from the other domain
         * so that when we access vaddr(pending_req,i) it has the contents of
         * the page from the other domain.
         */
        bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
        for (i = 0, j = 0; i < nseg; i++) {
                if (!persistent_gnts[i] ||
                    persistent_gnts[i]->handle == BLKBACK_INVALID_HANDLE) {
                        /* This is a newly mapped grant */
                        BUG_ON(j >= segs_to_map);
                        if (unlikely(map[j].status != 0)) {
                                pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
                                map[j].handle = BLKBACK_INVALID_HANDLE;
                                ret |= 1;
                                if (persistent_gnts[i]) {
                                        rb_erase(&persistent_gnts[i]->node,
                                                 &blkif->persistent_gnts);
                                        blkif->persistent_gnt_c--;
                                        kfree(persistent_gnts[i]);
                                        persistent_gnts[i] = NULL;
                                }
                        }
                }
                if (persistent_gnts[i]) {
                        if (persistent_gnts[i]->handle ==
                            BLKBACK_INVALID_HANDLE) {
                                /*
                                 * If this is a new persistent grant
                                 * save the handler
                                 */
                                persistent_gnts[i]->handle = map[j++].handle;
                        }
                        pending_handle(pending_req, i) =
                                persistent_gnts[i]->handle;

                        if (ret)
                                continue;
                } else {
                        pending_handle(pending_req, i) = map[j++].handle;
                        bitmap_set(pending_req->unmap_seg, i, 1);

                        if (ret)
                                continue;
                }
                seg[i].offset = (req->u.rw.seg[i].first_sect << 9);
        }
        return ret;
}

static int dispatch_discard_io(struct xen_blkif *blkif,
                                struct blkif_request *req)
{
        int err = 0;
        int status = BLKIF_RSP_OKAY;
        struct block_device *bdev = blkif->vbd.bdev;
        unsigned long secure;

        blkif->st_ds_req++;

        xen_blkif_get(blkif);
        secure = (blkif->vbd.discard_secure &&
                 (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
                 BLKDEV_DISCARD_SECURE : 0;

        err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
                                   req->u.discard.nr_sectors,
                                   GFP_KERNEL, secure);

        if (err == -EOPNOTSUPP) {
                pr_debug(DRV_PFX "discard op failed, not supported\n");
                status = BLKIF_RSP_EOPNOTSUPP;
        } else if (err)
                status = BLKIF_RSP_ERROR;

        make_response(blkif, req->u.discard.id, req->operation, status);
        xen_blkif_put(blkif);
        return err;
}

static int dispatch_other_io(struct xen_blkif *blkif,
                             struct blkif_request *req,
                             struct pending_req *pending_req)
{
        free_req(pending_req);
        make_response(blkif, req->u.other.id, req->operation,
                      BLKIF_RSP_EOPNOTSUPP);
        return -EIO;
}

static void xen_blk_drain_io(struct xen_blkif *blkif)
{
        atomic_set(&blkif->drain, 1);
        do {
                /* The initial value is one, and one refcnt taken at the
                 * start of the xen_blkif_schedule thread. */
                if (atomic_read(&blkif->refcnt) <= 2)
                        break;
                wait_for_completion_interruptible_timeout(
                                &blkif->drain_complete, HZ);

                if (!atomic_read(&blkif->drain))
                        break;
        } while (!kthread_should_stop());
        atomic_set(&blkif->drain, 0);
}

/*
 * Completion callback on the bio's. Called as bh->b_end_io()
 */

static void __end_block_io_op(struct pending_req *pending_req, int error)
{
        /* An error fails the entire request. */
        if ((pending_req->operation == BLKIF_OP_FLUSH_DISKCACHE) &&
            (error == -EOPNOTSUPP)) {
                pr_debug(DRV_PFX "flush diskcache op failed, not supported\n");
                xen_blkbk_flush_diskcache(XBT_NIL, pending_req->blkif->be, 0);
                pending_req->status = BLKIF_RSP_EOPNOTSUPP;
        } else if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) &&
                    (error == -EOPNOTSUPP)) {
                pr_debug(DRV_PFX "write barrier op failed, not supported\n");
                xen_blkbk_barrier(XBT_NIL, pending_req->blkif->be, 0);
                pending_req->status = BLKIF_RSP_EOPNOTSUPP;
        } else if (error) {
                pr_debug(DRV_PFX "Buffer not up-to-date at end of operation,"
                         " error=%d\n", error);
                pending_req->status = BLKIF_RSP_ERROR;
        }

        /*
         * If all of the bio's have completed it is time to unmap
         * the grant references associated with 'request' and provide
         * the proper response on the ring.
         */
        if (atomic_dec_and_test(&pending_req->pendcnt)) {
                xen_blkbk_unmap(pending_req);
                make_response(pending_req->blkif, pending_req->id,
                              pending_req->operation, pending_req->status);
                xen_blkif_put(pending_req->blkif);
                if (atomic_read(&pending_req->blkif->refcnt) <= 2) {
                        if (atomic_read(&pending_req->blkif->drain))
                                complete(&pending_req->blkif->drain_complete);
                }
                free_req(pending_req);
        }
}

/*
 * bio callback.
 */
static void end_block_io_op(struct bio *bio, int error)
{
        __end_block_io_op(bio->bi_private, error);
        bio_put(bio);
}



/*
 * Function to copy the from the ring buffer the 'struct blkif_request'
 * (which has the sectors we want, number of them, grant references, etc),
 * and transmute  it to the block API to hand it over to the proper block disk.
 */
static int
__do_block_io_op(struct xen_blkif *blkif)
{
        union blkif_back_rings *blk_rings = &blkif->blk_rings;
        struct blkif_request req;
        struct pending_req *pending_req;
        RING_IDX rc, rp;
        int more_to_do = 0;

        rc = blk_rings->common.req_cons;
        rp = blk_rings->common.sring->req_prod;
        rmb(); /* Ensure we see queued requests up to 'rp'. */

        while (rc != rp) {

                if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
                        break;

                if (kthread_should_stop()) {
                        more_to_do = 1;
                        break;
                }

                pending_req = alloc_req();
                if (NULL == pending_req) {
                        blkif->st_oo_req++;
                        more_to_do = 1;
                        break;
                }

                switch (blkif->blk_protocol) {
                case BLKIF_PROTOCOL_NATIVE:
                        memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
                        break;
                case BLKIF_PROTOCOL_X86_32:
                        blkif_get_x86_32_req(&req, RING_GET_REQUEST(&blk_rings->x86_32, rc));
                        break;
                case BLKIF_PROTOCOL_X86_64:
                        blkif_get_x86_64_req(&req, RING_GET_REQUEST(&blk_rings->x86_64, rc));
                        break;
                default:
                        BUG();
                }
                blk_rings->common.req_cons = ++rc; /* before make_response() */

                /* Apply all sanity checks to /private copy/ of request. */
                barrier();

                switch (req.operation) {
                case BLKIF_OP_READ:
                case BLKIF_OP_WRITE:
                case BLKIF_OP_WRITE_BARRIER:
                case BLKIF_OP_FLUSH_DISKCACHE:
                        if (dispatch_rw_block_io(blkif, &req, pending_req))
                                goto done;
                        break;
                case BLKIF_OP_DISCARD:
                        free_req(pending_req);
                        if (dispatch_discard_io(blkif, &req))
                                goto done;
                        break;
                default:
                        if (dispatch_other_io(blkif, &req, pending_req))
                                goto done;
                        break;
                }

                /* Yield point for this unbounded loop. */
                cond_resched();
        }
done:
        return more_to_do;
}

static int
do_block_io_op(struct xen_blkif *blkif)
{
        union blkif_back_rings *blk_rings = &blkif->blk_rings;
        int more_to_do;

        do {
                more_to_do = __do_block_io_op(blkif);
                if (more_to_do)
                        break;

                RING_FINAL_CHECK_FOR_REQUESTS(&blk_rings->common, more_to_do);
        } while (more_to_do);

        return more_to_do;
}
/*
 * Transmutation of the 'struct blkif_request' to a proper 'struct bio'
 * and call the 'submit_bio' to pass it to the underlying storage.
 */
static int dispatch_rw_block_io(struct xen_blkif *blkif,
                                struct blkif_request *req,
                                struct pending_req *pending_req)
{
        struct phys_req preq;
        struct seg_buf seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        unsigned int nseg;
        struct bio *bio = NULL;
        struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        int i, nbio = 0;
        int operation;
        struct blk_plug plug;
        bool drain = false;
        struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];

        switch (req->operation) {
        case BLKIF_OP_READ:
                blkif->st_rd_req++;
                operation = READ;
                break;
        case BLKIF_OP_WRITE:
                blkif->st_wr_req++;
                operation = WRITE_ODIRECT;
                break;
        case BLKIF_OP_WRITE_BARRIER:
                drain = true;
        case BLKIF_OP_FLUSH_DISKCACHE:
                blkif->st_f_req++;
                operation = WRITE_FLUSH;
                break;
        default:
                operation = 0; /* make gcc happy */
                goto fail_response;
                break;
        }

        /* Check that the number of segments is sane. */
        nseg = req->u.rw.nr_segments;

        if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
            unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
                pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
                         nseg);
                /* Haven't submitted any bio's yet. */
                goto fail_response;
        }

        preq.sector_number = req->u.rw.sector_number;
        preq.nr_sects      = 0;

        pending_req->blkif     = blkif;
        pending_req->id        = req->u.rw.id;
        pending_req->operation = req->operation;
        pending_req->status    = BLKIF_RSP_OKAY;
        pending_req->nr_pages  = nseg;

        for (i = 0; i < nseg; i++) {
                seg[i].nsec = req->u.rw.seg[i].last_sect -
                        req->u.rw.seg[i].first_sect + 1;
                if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
                    (req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect))
                        goto fail_response;
                preq.nr_sects += seg[i].nsec;

        }

        if (xen_vbd_translate(&preq, blkif, operation) != 0) {
                pr_debug(DRV_PFX "access denied: %s of [%llu,%llu] on dev=%04x\n",
                         operation == READ ? "read" : "write",
                         preq.sector_number,
                         preq.sector_number + preq.nr_sects,
                         blkif->vbd.pdevice);
                goto fail_response;
        }

        /*
         * This check _MUST_ be done after xen_vbd_translate as the preq.bdev
         * is set there.
         */
        for (i = 0; i < nseg; i++) {
                if (((int)preq.sector_number|(int)seg[i].nsec) &
                    ((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
                        pr_debug(DRV_PFX "Misaligned I/O request from domain %d",
                                 blkif->domid);
                        goto fail_response;
                }
        }

        /* Wait on all outstanding I/O's and once that has been completed
         * issue the WRITE_FLUSH.
         */
        if (drain)
                xen_blk_drain_io(pending_req->blkif);

        /*
         * If we have failed at this point, we need to undo the M2P override,
         * set gnttab_set_unmap_op on all of the grant references and perform
         * the hypercall to unmap the grants - that is all done in
         * xen_blkbk_unmap.
         */
        if (xen_blkbk_map(req, pending_req, seg, pages))
                goto fail_flush;

        /*
         * This corresponding xen_blkif_put is done in __end_block_io_op, or
         * below (in "!bio") if we are handling a BLKIF_OP_DISCARD.
         */
        xen_blkif_get(blkif);

        for (i = 0; i < nseg; i++) {
                while ((bio == NULL) ||
                       (bio_add_page(bio,
                                     pages[i],
                                     seg[i].nsec << 9,
                                     seg[i].offset) == 0)) {

                        bio = bio_alloc(GFP_KERNEL, nseg-i);
                        if (unlikely(bio == NULL))
                                goto fail_put_bio;

                        biolist[nbio++] = bio;
                        bio->bi_bdev    = preq.bdev;
                        bio->bi_private = pending_req;
                        bio->bi_end_io  = end_block_io_op;
                        bio->bi_sector  = preq.sector_number;
                }

                preq.sector_number += seg[i].nsec;
        }

        /* This will be hit if the operation was a flush or discard. */
        if (!bio) {
                BUG_ON(operation != WRITE_FLUSH);

                bio = bio_alloc(GFP_KERNEL, 0);
                if (unlikely(bio == NULL))
                        goto fail_put_bio;

                biolist[nbio++] = bio;
                bio->bi_bdev    = preq.bdev;
                bio->bi_private = pending_req;
                bio->bi_end_io  = end_block_io_op;
        }

        atomic_set(&pending_req->pendcnt, nbio);
        blk_start_plug(&plug);

        for (i = 0; i < nbio; i++)
                submit_bio(operation, biolist[i]);

        /* Let the I/Os go.. */
        blk_finish_plug(&plug);

        if (operation == READ)
                blkif->st_rd_sect += preq.nr_sects;
        else if (operation & WRITE)
                blkif->st_wr_sect += preq.nr_sects;

        return 0;

 fail_flush:
        xen_blkbk_unmap(pending_req);
 fail_response:
        /* Haven't submitted any bio's yet. */
        make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
        free_req(pending_req);
        msleep(1); /* back off a bit */
        return -EIO;

 fail_put_bio:
        for (i = 0; i < nbio; i++)
                bio_put(biolist[i]);
        atomic_set(&pending_req->pendcnt, 1);
        __end_block_io_op(pending_req, -EINVAL);
        msleep(1); /* back off a bit */
        return -EIO;
}



/*
 * Put a response on the ring on how the operation fared.
 */
static void make_response(struct xen_blkif *blkif, u64 id,
                          unsigned short op, int st)
{
        struct blkif_response  resp;
        unsigned long     flags;
        union blkif_back_rings *blk_rings = &blkif->blk_rings;
        int notify;

        resp.id        = id;
        resp.operation = op;
        resp.status    = st;

        spin_lock_irqsave(&blkif->blk_ring_lock, flags);
        /* Place on the response ring for the relevant domain. */
        switch (blkif->blk_protocol) {
        case BLKIF_PROTOCOL_NATIVE:
                memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
                       &resp, sizeof(resp));
                break;
        case BLKIF_PROTOCOL_X86_32:
                memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
                       &resp, sizeof(resp));
                break;
        case BLKIF_PROTOCOL_X86_64:
                memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
                       &resp, sizeof(resp));
                break;
        default:
                BUG();
        }
        blk_rings->common.rsp_prod_pvt++;
        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
        spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
        if (notify)
                notify_remote_via_irq(blkif->irq);
}

static int __init xen_blkif_init(void)
{
        int i, mmap_pages;
        int rc = 0;

        if (!xen_domain())
                return -ENODEV;

        blkbk = kzalloc(sizeof(struct xen_blkbk), GFP_KERNEL);
        if (!blkbk) {
                pr_alert(DRV_PFX "%s: out of memory!\n", __func__);
                return -ENOMEM;
        }

        mmap_pages = xen_blkif_reqs * BLKIF_MAX_SEGMENTS_PER_REQUEST;

        blkbk->pending_reqs          = kzalloc(sizeof(blkbk->pending_reqs[0]) *
                                        xen_blkif_reqs, GFP_KERNEL);
        blkbk->pending_grant_handles = kmalloc(sizeof(blkbk->pending_grant_handles[0]) *
                                        mmap_pages, GFP_KERNEL);
        blkbk->pending_pages         = kzalloc(sizeof(blkbk->pending_pages[0]) *
                                        mmap_pages, GFP_KERNEL);

        if (!blkbk->pending_reqs || !blkbk->pending_grant_handles ||
            !blkbk->pending_pages) {
                rc = -ENOMEM;
                goto out_of_memory;
        }

        for (i = 0; i < mmap_pages; i++) {
                blkbk->pending_grant_handles[i] = BLKBACK_INVALID_HANDLE;
                blkbk->pending_pages[i] = alloc_page(GFP_KERNEL);
                if (blkbk->pending_pages[i] == NULL) {
                        rc = -ENOMEM;
                        goto out_of_memory;
                }
        }
        rc = xen_blkif_interface_init();
        if (rc)
                goto failed_init;

        INIT_LIST_HEAD(&blkbk->pending_free);
        spin_lock_init(&blkbk->pending_free_lock);
        init_waitqueue_head(&blkbk->pending_free_wq);

        for (i = 0; i < xen_blkif_reqs; i++)
                list_add_tail(&blkbk->pending_reqs[i].free_list,
                              &blkbk->pending_free);

        rc = xen_blkif_xenbus_init();
        if (rc)
                goto failed_init;

        return 0;

 out_of_memory:
        pr_alert(DRV_PFX "%s: out of memory\n", __func__);
 failed_init:
        kfree(blkbk->pending_reqs);
        kfree(blkbk->pending_grant_handles);
        if (blkbk->pending_pages) {
                for (i = 0; i < mmap_pages; i++) {
                        if (blkbk->pending_pages[i])
                                __free_page(blkbk->pending_pages[i]);
                }
                kfree(blkbk->pending_pages);
        }
        kfree(blkbk);
        blkbk = NULL;
        return rc;
}

module_init(xen_blkif_init);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("xen-backend:vbd");