/*
 * The Virtio 9p transport driver
 *
 * This is a block based transport driver based on the lguest block driver
 * code.
 *
 *  Copyright (C) 2007, 2008 Eric Van Hensbergen, IBM Corporation
 *
 *  Based on virtio console driver
 *  Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
 *
 *  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.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to:
 *  Free Software Foundation
 *  51 Franklin Street, Fifth Floor
 *  Boston, MA  02111-1301  USA
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/in.h>
#include <linux/module.h>
#include <linux/net.h>
#include <linux/ipv6.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/un.h>
#include <linux/uaccess.h>
#include <linux/inet.h>
#include <linux/idr.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <net/9p/9p.h>
#include <linux/parser.h>
#include <net/9p/client.h>
#include <net/9p/transport.h>
#include <linux/scatterlist.h>
#include <linux/swap.h>
#include <linux/virtio.h>
#include <linux/virtio_9p.h>
#include "trans_common.h"

#define VIRTQUEUE_NUM   128

/* a single mutex to manage channel initialization and attachment */
static DEFINE_MUTEX(virtio_9p_lock);
static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
static atomic_t vp_pinned = ATOMIC_INIT(0);

/**
 * struct virtio_chan - per-instance transport information
 * @initialized: whether the channel is initialized
 * @inuse: whether the channel is in use
 * @lock: protects multiple elements within this structure
 * @client: client instance
 * @vdev: virtio dev associated with this channel
 * @vq: virtio queue associated with this channel
 * @sg: scatter gather list which is used to pack a request (protected?)
 *
 * We keep all per-channel information in a structure.
 * This structure is allocated within the devices dev->mem space.
 * A pointer to the structure will get put in the transport private.
 *
 */

struct virtio_chan {
        bool inuse;

        spinlock_t lock;

        struct p9_client *client;
        struct virtio_device *vdev;
        struct virtqueue *vq;
        int ring_bufs_avail;
        wait_queue_head_t *vc_wq;
        /* This is global limit. Since we don't have a global structure,
         * will be placing it in each channel.
         */
        unsigned long p9_max_pages;
        /* Scatterlist: can be too big for stack. */
        struct scatterlist sg[VIRTQUEUE_NUM];

        int tag_len;
        /*
         * tag name to identify a mount Non-null terminated
         */
        char *tag;

        struct list_head chan_list;
};

static struct list_head virtio_chan_list;

/* How many bytes left in this page. */
static unsigned int rest_of_page(void *data)
{
        return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
}

/**
 * p9_virtio_close - reclaim resources of a channel
 * @client: client instance
 *
 * This reclaims a channel by freeing its resources and
 * reseting its inuse flag.
 *
 */

static void p9_virtio_close(struct p9_client *client)
{
        struct virtio_chan *chan = client->trans;

        mutex_lock(&virtio_9p_lock);
        if (chan)
                chan->inuse = false;
        mutex_unlock(&virtio_9p_lock);
}

/**
 * req_done - callback which signals activity from the server
 * @vq: virtio queue activity was received on
 *
 * This notifies us that the server has triggered some activity
 * on the virtio channel - most likely a response to request we
 * sent.  Figure out which requests now have responses and wake up
 * those threads.
 *
 * Bugs: could do with some additional sanity checking, but appears to work.
 *
 */

static void req_done(struct virtqueue *vq)
{
        struct virtio_chan *chan = vq->vdev->priv;
        struct p9_fcall *rc;
        unsigned int len;
        struct p9_req_t *req;
        unsigned long flags;

        p9_debug(P9_DEBUG_TRANS, ": request done\n");

        while (1) {
                spin_lock_irqsave(&chan->lock, flags);
                rc = virtqueue_get_buf(chan->vq, &len);
                if (rc == NULL) {
                        spin_unlock_irqrestore(&chan->lock, flags);
                        break;
                }
                chan->ring_bufs_avail = 1;
                spin_unlock_irqrestore(&chan->lock, flags);
                /* Wakeup if anyone waiting for VirtIO ring space. */
                wake_up(chan->vc_wq);
                p9_debug(P9_DEBUG_TRANS, ": rc %p\n", rc);
                p9_debug(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
                req = p9_tag_lookup(chan->client, rc->tag);
                p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
        }
}

/**
 * pack_sg_list - pack a scatter gather list from a linear buffer
 * @sg: scatter/gather list to pack into
 * @start: which segment of the sg_list to start at
 * @limit: maximum segment to pack data to
 * @data: data to pack into scatter/gather list
 * @count: amount of data to pack into the scatter/gather list
 *
 * sg_lists have multiple segments of various sizes.  This will pack
 * arbitrary data into an existing scatter gather list, segmenting the
 * data as necessary within constraints.
 *
 */

static int pack_sg_list(struct scatterlist *sg, int start,
                        int limit, char *data, int count)
{
        int s;
        int index = start;

        while (count) {
                s = rest_of_page(data);
                if (s > count)
                        s = count;
                BUG_ON(index > limit);
                /* Make sure we don't terminate early. */
                sg_unmark_end(&sg[index]);
                sg_set_buf(&sg[index++], data, s);
                count -= s;
                data += s;
        }
        if (index-start)
                sg_mark_end(&sg[index - 1]);
        return index-start;
}

/* We don't currently allow canceling of virtio requests */
static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
{
        return 1;
}

/**
 * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
 * this takes a list of pages.
 * @sg: scatter/gather list to pack into
 * @start: which segment of the sg_list to start at
 * @pdata: a list of pages to add into sg.
 * @nr_pages: number of pages to pack into the scatter/gather list
 * @offs: amount of data in the beginning of first page _not_ to pack
 * @count: amount of data to pack into the scatter/gather list
 */
static int
pack_sg_list_p(struct scatterlist *sg, int start, int limit,
               struct page **pdata, int nr_pages, size_t offs, int count)
{
        int i = 0, s;
        int data_off = offs;
        int index = start;

        BUG_ON(nr_pages > (limit - start));
        /*
         * if the first page doesn't start at
         * page boundary find the offset
         */
        while (nr_pages) {
                s = PAGE_SIZE - data_off;
                if (s > count)
                        s = count;
                /* Make sure we don't terminate early. */
                sg_unmark_end(&sg[index]);
                sg_set_page(&sg[index++], pdata[i++], s, data_off);
                data_off = 0;
                count -= s;
                nr_pages--;
        }

        if (index-start)
                sg_mark_end(&sg[index - 1]);
        return index - start;
}

/**
 * p9_virtio_request - issue a request
 * @client: client instance issuing the request
 * @req: request to be issued
 *
 */

static int
p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
{
        int err;
        int in, out, out_sgs, in_sgs;
        unsigned long flags;
        struct virtio_chan *chan = client->trans;
        struct scatterlist *sgs[2];

        p9_debug(P9_DEBUG_TRANS, "9p debug: virtio request\n");

        req->status = REQ_STATUS_SENT;
req_retry:
        spin_lock_irqsave(&chan->lock, flags);

        out_sgs = in_sgs = 0;
        /* Handle out VirtIO ring buffers */
        out = pack_sg_list(chan->sg, 0,
                           VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
        if (out)
                sgs[out_sgs++] = chan->sg;

        in = pack_sg_list(chan->sg, out,
                          VIRTQUEUE_NUM, req->rc->sdata, req->rc->capacity);
        if (in)
                sgs[out_sgs + in_sgs++] = chan->sg + out;

        err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
                                GFP_ATOMIC);
        if (err < 0) {
                if (err == -ENOSPC) {
                        chan->ring_bufs_avail = 0;
                        spin_unlock_irqrestore(&chan->lock, flags);
                        err = wait_event_interruptible(*chan->vc_wq,
                                                        chan->ring_bufs_avail);
                        if (err  == -ERESTARTSYS)
                                return err;

                        p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
                        goto req_retry;
                } else {
                        spin_unlock_irqrestore(&chan->lock, flags);
                        p9_debug(P9_DEBUG_TRANS,
                                 "virtio rpc add_sgs returned failure\n");
                        return -EIO;
                }
        }
        virtqueue_kick(chan->vq);
        spin_unlock_irqrestore(&chan->lock, flags);

        p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
        return 0;
}

static int p9_get_mapped_pages(struct virtio_chan *chan,
                               struct page ***pages,
                               struct iov_iter *data,
                               int count,
                               size_t *offs,
                               int *need_drop)
{
        int nr_pages;
        int err;

        if (!iov_iter_count(data))
                return 0;

        if (!(data->type & ITER_KVEC)) {
                int n;
                /*
                 * We allow only p9_max_pages pinned. We wait for the
                 * Other zc request to finish here
                 */
                if (atomic_read(&vp_pinned) >= chan->p9_max_pages) {
                        err = wait_event_interruptible(vp_wq,
                              (atomic_read(&vp_pinned) < chan->p9_max_pages));
                        if (err == -ERESTARTSYS)
                                return err;
                }
                n = iov_iter_get_pages_alloc(data, pages, count, offs);
                if (n < 0)
                        return n;
                *need_drop = 1;
                nr_pages = DIV_ROUND_UP(n + *offs, PAGE_SIZE);
                atomic_add(nr_pages, &vp_pinned);
                return n;
        } else {
                /* kernel buffer, no need to pin pages */
                int index;
                size_t len;
                void *p;

                /* we'd already checked that it's non-empty */
                while (1) {
                        len = iov_iter_single_seg_count(data);
                        if (likely(len)) {
                                p = data->kvec->iov_base + data->iov_offset;
                                break;
                        }
                        iov_iter_advance(data, 0);
                }
                if (len > count)
                        len = count;

                nr_pages = DIV_ROUND_UP((unsigned long)p + len, PAGE_SIZE) -
                           (unsigned long)p / PAGE_SIZE;

                *pages = kmalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
                if (!*pages)
                        return -ENOMEM;

                *need_drop = 0;
                p -= (*offs = (unsigned long)p % PAGE_SIZE);
                for (index = 0; index < nr_pages; index++) {
                        if (is_vmalloc_addr(p))
                                (*pages)[index] = vmalloc_to_page(p);
                        else
                                (*pages)[index] = kmap_to_page(p);
                        p += PAGE_SIZE;
                }
                return len;
        }
}

/**
 * p9_virtio_zc_request - issue a zero copy request
 * @client: client instance issuing the request
 * @req: request to be issued
 * @uidata: user bffer that should be ued for zero copy read
 * @uodata: user buffer that shoud be user for zero copy write
 * @inlen: read buffer size
 * @olen: write buffer size
 * @hdrlen: reader header size, This is the size of response protocol data
 *
 */
static int
p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
                     struct iov_iter *uidata, struct iov_iter *uodata,
                     int inlen, int outlen, int in_hdr_len)
{
        int in, out, err, out_sgs, in_sgs;
        unsigned long flags;
        int in_nr_pages = 0, out_nr_pages = 0;
        struct page **in_pages = NULL, **out_pages = NULL;
        struct virtio_chan *chan = client->trans;
        struct scatterlist *sgs[4];
        size_t offs;
        int need_drop = 0;

        p9_debug(P9_DEBUG_TRANS, "virtio request\n");

        if (uodata) {
                int n = p9_get_mapped_pages(chan, &out_pages, uodata,
                                            outlen, &offs, &need_drop);
                if (n < 0)
                        return n;
                out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
                if (n != outlen) {
                        __le32 v = cpu_to_le32(n);
                        memcpy(&req->tc->sdata[req->tc->size - 4], &v, 4);
                        outlen = n;
                }
        } else if (uidata) {
                int n = p9_get_mapped_pages(chan, &in_pages, uidata,
                                            inlen, &offs, &need_drop);
                if (n < 0)
                        return n;
                in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
                if (n != inlen) {
                        __le32 v = cpu_to_le32(n);
                        memcpy(&req->tc->sdata[req->tc->size - 4], &v, 4);
                        inlen = n;
                }
        }
        req->status = REQ_STATUS_SENT;
req_retry_pinned:
        spin_lock_irqsave(&chan->lock, flags);

        out_sgs = in_sgs = 0;

        /* out data */
        out = pack_sg_list(chan->sg, 0,
                           VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);

        if (out)
                sgs[out_sgs++] = chan->sg;

        if (out_pages) {
                sgs[out_sgs++] = chan->sg + out;
                out += pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
                                      out_pages, out_nr_pages, offs, outlen);
        }
                
        /*
         * Take care of in data
         * For example TREAD have 11.
         * 11 is the read/write header = PDU Header(7) + IO Size (4).
         * Arrange in such a way that server places header in the
         * alloced memory and payload onto the user buffer.
         */
        in = pack_sg_list(chan->sg, out,
                          VIRTQUEUE_NUM, req->rc->sdata, in_hdr_len);
        if (in)
                sgs[out_sgs + in_sgs++] = chan->sg + out;

        if (in_pages) {
                sgs[out_sgs + in_sgs++] = chan->sg + out + in;
                in += pack_sg_list_p(chan->sg, out + in, VIRTQUEUE_NUM,
                                     in_pages, in_nr_pages, offs, inlen);
        }

        BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
        err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
                                GFP_ATOMIC);
        if (err < 0) {
                if (err == -ENOSPC) {
                        chan->ring_bufs_avail = 0;
                        spin_unlock_irqrestore(&chan->lock, flags);
                        err = wait_event_interruptible(*chan->vc_wq,
                                                       chan->ring_bufs_avail);
                        if (err  == -ERESTARTSYS)
                                goto err_out;

                        p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
                        goto req_retry_pinned;
                } else {
                        spin_unlock_irqrestore(&chan->lock, flags);
                        p9_debug(P9_DEBUG_TRANS,
                                 "virtio rpc add_sgs returned failure\n");
                        err = -EIO;
                        goto err_out;
                }
        }
        virtqueue_kick(chan->vq);
        spin_unlock_irqrestore(&chan->lock, flags);
        p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
        err = wait_event_interruptible(*req->wq,
                                       req->status >= REQ_STATUS_RCVD);
        /*
         * Non kernel buffers are pinned, unpin them
         */
err_out:
        if (need_drop) {
                if (in_pages) {
                        p9_release_pages(in_pages, in_nr_pages);
                        atomic_sub(in_nr_pages, &vp_pinned);
                }
                if (out_pages) {
                        p9_release_pages(out_pages, out_nr_pages);
                        atomic_sub(out_nr_pages, &vp_pinned);
                }
                /* wakeup anybody waiting for slots to pin pages */
                wake_up(&vp_wq);
        }
        kfree(in_pages);
        kfree(out_pages);
        return err;
}

static ssize_t p9_mount_tag_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct virtio_chan *chan;
        struct virtio_device *vdev;

        vdev = dev_to_virtio(dev);
        chan = vdev->priv;

        memcpy(buf, chan->tag, chan->tag_len);
        buf[chan->tag_len] = 0;

        return chan->tag_len + 1;
}

static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);

/**
 * p9_virtio_probe - probe for existence of 9P virtio channels
 * @vdev: virtio device to probe
 *
 * This probes for existing virtio channels.
 *
 */

static int p9_virtio_probe(struct virtio_device *vdev)
{
        __u16 tag_len;
        char *tag;
        int err;
        struct virtio_chan *chan;

        if (!vdev->config->get) {
                dev_err(&vdev->dev, "%s failure: config access disabled\n",
                        __func__);
                return -EINVAL;
        }

        chan = kmalloc(sizeof(struct virtio_chan), GFP_KERNEL);
        if (!chan) {
                pr_err("Failed to allocate virtio 9P channel\n");
                err = -ENOMEM;
                goto fail;
        }

        chan->vdev = vdev;

        /* We expect one virtqueue, for requests. */
        chan->vq = virtio_find_single_vq(vdev, req_done, "requests");
        if (IS_ERR(chan->vq)) {
                err = PTR_ERR(chan->vq);
                goto out_free_vq;
        }
        chan->vq->vdev->priv = chan;
        spin_lock_init(&chan->lock);

        sg_init_table(chan->sg, VIRTQUEUE_NUM);

        chan->inuse = false;
        if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
                virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
        } else {
                err = -EINVAL;
                goto out_free_vq;
        }
        tag = kmalloc(tag_len, GFP_KERNEL);
        if (!tag) {
                err = -ENOMEM;
                goto out_free_vq;
        }

        virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
                           tag, tag_len);
        chan->tag = tag;
        chan->tag_len = tag_len;
        err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
        if (err) {
                goto out_free_tag;
        }
        chan->vc_wq = kmalloc(sizeof(wait_queue_head_t), GFP_KERNEL);
        if (!chan->vc_wq) {
                err = -ENOMEM;
                goto out_free_tag;
        }
        init_waitqueue_head(chan->vc_wq);
        chan->ring_bufs_avail = 1;
        /* Ceiling limit to avoid denial of service attacks */
        chan->p9_max_pages = nr_free_buffer_pages()/4;

        virtio_device_ready(vdev);

        mutex_lock(&virtio_9p_lock);
        list_add_tail(&chan->chan_list, &virtio_chan_list);
        mutex_unlock(&virtio_9p_lock);

        /* Let udev rules use the new mount_tag attribute. */
        kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);

        return 0;

out_free_tag:
        kfree(tag);
out_free_vq:
        vdev->config->del_vqs(vdev);
        kfree(chan);
fail:
        return err;
}


/**
 * p9_virtio_create - allocate a new virtio channel
 * @client: client instance invoking this transport
 * @devname: string identifying the channel to connect to (unused)
 * @args: args passed from sys_mount() for per-transport options (unused)
 *
 * This sets up a transport channel for 9p communication.  Right now
 * we only match the first available channel, but eventually we couldlook up
 * alternate channels by matching devname versus a virtio_config entry.
 * We use a simple reference count mechanism to ensure that only a single
 * mount has a channel open at a time.
 *
 */

static int
p9_virtio_create(struct p9_client *client, const char *devname, char *args)
{
        struct virtio_chan *chan;
        int ret = -ENOENT;
        int found = 0;

        mutex_lock(&virtio_9p_lock);
        list_for_each_entry(chan, &virtio_chan_list, chan_list) {
                if (!strncmp(devname, chan->tag, chan->tag_len) &&
                    strlen(devname) == chan->tag_len) {
                        if (!chan->inuse) {
                                chan->inuse = true;
                                found = 1;
                                break;
                        }
                        ret = -EBUSY;
                }
        }
        mutex_unlock(&virtio_9p_lock);

        if (!found) {
                pr_err("no channels available\n");
                return ret;
        }

        client->trans = (void *)chan;
        client->status = Connected;
        chan->client = client;

        return 0;
}

/**
 * p9_virtio_remove - clean up resources associated with a virtio device
 * @vdev: virtio device to remove
 *
 */

static void p9_virtio_remove(struct virtio_device *vdev)
{
        struct virtio_chan *chan = vdev->priv;
        unsigned long warning_time;

        mutex_lock(&virtio_9p_lock);

        /* Remove self from list so we don't get new users. */
        list_del(&chan->chan_list);
        warning_time = jiffies;

        /* Wait for existing users to close. */
        while (chan->inuse) {
                mutex_unlock(&virtio_9p_lock);
                msleep(250);
                if (time_after(jiffies, warning_time + 10 * HZ)) {
                        dev_emerg(&vdev->dev,
                                  "p9_virtio_remove: waiting for device in use.\n");
                        warning_time = jiffies;
                }
                mutex_lock(&virtio_9p_lock);
        }

        mutex_unlock(&virtio_9p_lock);

        vdev->config->del_vqs(vdev);

        sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
        kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
        kfree(chan->tag);
        kfree(chan->vc_wq);
        kfree(chan);

}

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_9P, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static unsigned int features[] = {
        VIRTIO_9P_MOUNT_TAG,
};

/* The standard "struct lguest_driver": */
static struct virtio_driver p9_virtio_drv = {
        .feature_table  = features,
        .feature_table_size = ARRAY_SIZE(features),
        .driver.name    = KBUILD_MODNAME,
        .driver.owner   = THIS_MODULE,
        .id_table       = id_table,
        .probe          = p9_virtio_probe,
        .remove         = p9_virtio_remove,
};

static struct p9_trans_module p9_virtio_trans = {
        .name = "virtio",
        .create = p9_virtio_create,
        .close = p9_virtio_close,
        .request = p9_virtio_request,
        .zc_request = p9_virtio_zc_request,
        .cancel = p9_virtio_cancel,
        /*
         * We leave one entry for input and one entry for response
         * headers. We also skip one more entry to accomodate, address
         * that are not at page boundary, that can result in an extra
         * page in zero copy.
         */
        .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
        .def = 1,
        .owner = THIS_MODULE,
};

/* The standard init function */
static int __init p9_virtio_init(void)
{
        INIT_LIST_HEAD(&virtio_chan_list);

        v9fs_register_trans(&p9_virtio_trans);
        return register_virtio_driver(&p9_virtio_drv);
}

static void __exit p9_virtio_cleanup(void)
{
        unregister_virtio_driver(&p9_virtio_drv);
        v9fs_unregister_trans(&p9_virtio_trans);
}

module_init(p9_virtio_init);
module_exit(p9_virtio_cleanup);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_AUTHOR("Eric Van Hensbergen <ericvh@gmail.com>");
MODULE_DESCRIPTION("Virtio 9p Transport");
MODULE_LICENSE("GPL");