virtio: console: open: Use a common path for error handling

[linux-flexiantxendom0-3.2.10.git] / drivers / char / virtio_console.c

/*
 * Copyright (C) 2006, 2007, 2009 Rusty Russell, IBM Corporation
 * Copyright (C) 2009, 2010 Red Hat, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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 the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
#include <linux/cdev.h>
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/virtio.h>
#include <linux/virtio_console.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include "hvc_console.h"

/*
 * This is a global struct for storing common data for all the devices
 * this driver handles.
 *
 * Mainly, it has a linked list for all the consoles in one place so
 * that callbacks from hvc for get_chars(), put_chars() work properly
 * across multiple devices and multiple ports per device.
 */
struct ports_driver_data {
        /* Used for registering chardevs */
        struct class *class;

        /* Used for exporting per-port information to debugfs */
        struct dentry *debugfs_dir;

        /* Number of devices this driver is handling */
        unsigned int index;

        /*
         * This is used to keep track of the number of hvc consoles
         * spawned by this driver.  This number is given as the first
         * argument to hvc_alloc().  To correctly map an initial
         * console spawned via hvc_instantiate to the console being
         * hooked up via hvc_alloc, we need to pass the same vtermno.
         *
         * We also just assume the first console being initialised was
         * the first one that got used as the initial console.
         */
        unsigned int next_vtermno;

        /* All the console devices handled by this driver */
        struct list_head consoles;
};
static struct ports_driver_data pdrvdata;

DEFINE_SPINLOCK(pdrvdata_lock);

/* This struct holds information that's relevant only for console ports */
struct console {
        /* We'll place all consoles in a list in the pdrvdata struct */
        struct list_head list;

        /* The hvc device associated with this console port */
        struct hvc_struct *hvc;

        /* The size of the console */
        struct winsize ws;

        /*
         * This number identifies the number that we used to register
         * with hvc in hvc_instantiate() and hvc_alloc(); this is the
         * number passed on by the hvc callbacks to us to
         * differentiate between the other console ports handled by
         * this driver
         */
        u32 vtermno;
};

struct port_buffer {
        char *buf;

        /* size of the buffer in *buf above */
        size_t size;

        /* used length of the buffer */
        size_t len;
        /* offset in the buf from which to consume data */
        size_t offset;
};

/*
 * This is a per-device struct that stores data common to all the
 * ports for that device (vdev->priv).
 */
struct ports_device {
        /*
         * Workqueue handlers where we process deferred work after
         * notification
         */
        struct work_struct control_work;

        struct list_head ports;

        /* To protect the list of ports */
        spinlock_t ports_lock;

        /* To protect the vq operations for the control channel */
        spinlock_t cvq_lock;

        /* The current config space is stored here */
        struct virtio_console_config config;

        /* The virtio device we're associated with */
        struct virtio_device *vdev;

        /*
         * A couple of virtqueues for the control channel: one for
         * guest->host transfers, one for host->guest transfers
         */
        struct virtqueue *c_ivq, *c_ovq;

        /* Array of per-port IO virtqueues */
        struct virtqueue **in_vqs, **out_vqs;

        /* Used for numbering devices for sysfs and debugfs */
        unsigned int drv_index;

        /* Major number for this device.  Ports will be created as minors. */
        int chr_major;
};

/* This struct holds the per-port data */
struct port {
        /* Next port in the list, head is in the ports_device */
        struct list_head list;

        /* Pointer to the parent virtio_console device */
        struct ports_device *portdev;

        /* The current buffer from which data has to be fed to readers */
        struct port_buffer *inbuf;

        /*
         * To protect the operations on the in_vq associated with this
         * port.  Has to be a spinlock because it can be called from
         * interrupt context (get_char()).
         */
        spinlock_t inbuf_lock;

        /* Protect the operations on the out_vq. */
        spinlock_t outvq_lock;

        /* The IO vqs for this port */
        struct virtqueue *in_vq, *out_vq;

        /* File in the debugfs directory that exposes this port's information */
        struct dentry *debugfs_file;

        /*
         * The entries in this struct will be valid if this port is
         * hooked up to an hvc console
         */
        struct console cons;

        /* Each port associates with a separate char device */
        struct cdev cdev;
        struct device *dev;

        /* A waitqueue for poll() or blocking read operations */
        wait_queue_head_t waitqueue;

        /* The 'name' of the port that we expose via sysfs properties */
        char *name;

        /* The 'id' to identify the port with the Host */
        u32 id;

        bool outvq_full;

        /* Is the host device open */
        bool host_connected;

        /* We should allow only one process to open a port */
        bool guest_connected;
};

/* This is the very early arch-specified put chars function. */
static int (*early_put_chars)(u32, const char *, int);

static struct port *find_port_by_vtermno(u32 vtermno)
{
        struct port *port;
        struct console *cons;
        unsigned long flags;

        spin_lock_irqsave(&pdrvdata_lock, flags);
        list_for_each_entry(cons, &pdrvdata.consoles, list) {
                if (cons->vtermno == vtermno) {
                        port = container_of(cons, struct port, cons);
                        goto out;
                }
        }
        port = NULL;
out:
        spin_unlock_irqrestore(&pdrvdata_lock, flags);
        return port;
}

static struct port *find_port_by_id(struct ports_device *portdev, u32 id)
{
        struct port *port;
        unsigned long flags;

        spin_lock_irqsave(&portdev->ports_lock, flags);
        list_for_each_entry(port, &portdev->ports, list)
                if (port->id == id)
                        goto out;
        port = NULL;
out:
        spin_unlock_irqrestore(&portdev->ports_lock, flags);

        return port;
}

static struct port *find_port_by_vq(struct ports_device *portdev,
                                    struct virtqueue *vq)
{
        struct port *port;
        unsigned long flags;

        spin_lock_irqsave(&portdev->ports_lock, flags);
        list_for_each_entry(port, &portdev->ports, list)
                if (port->in_vq == vq || port->out_vq == vq)
                        goto out;
        port = NULL;
out:
        spin_unlock_irqrestore(&portdev->ports_lock, flags);
        return port;
}

static bool is_console_port(struct port *port)
{
        if (port->cons.hvc)
                return true;
        return false;
}

static inline bool use_multiport(struct ports_device *portdev)
{
        /*
         * This condition can be true when put_chars is called from
         * early_init
         */
        if (!portdev->vdev)
                return 0;
        return portdev->vdev->features[0] & (1 << VIRTIO_CONSOLE_F_MULTIPORT);
}

static void free_buf(struct port_buffer *buf)
{
        kfree(buf->buf);
        kfree(buf);
}

static struct port_buffer *alloc_buf(size_t buf_size)
{
        struct port_buffer *buf;

        buf = kmalloc(sizeof(*buf), GFP_KERNEL);
        if (!buf)
                goto fail;
        buf->buf = kzalloc(buf_size, GFP_KERNEL);
        if (!buf->buf)
                goto free_buf;
        buf->len = 0;
        buf->offset = 0;
        buf->size = buf_size;
        return buf;

free_buf:
        kfree(buf);
fail:
        return NULL;
}

/* Callers should take appropriate locks */
static void *get_inbuf(struct port *port)
{
        struct port_buffer *buf;
        struct virtqueue *vq;
        unsigned int len;

        vq = port->in_vq;
        buf = virtqueue_get_buf(vq, &len);
        if (buf) {
                buf->len = len;
                buf->offset = 0;
        }
        return buf;
}

/*
 * Create a scatter-gather list representing our input buffer and put
 * it in the queue.
 *
 * Callers should take appropriate locks.
 */
static int add_inbuf(struct virtqueue *vq, struct port_buffer *buf)
{
        struct scatterlist sg[1];
        int ret;

        sg_init_one(sg, buf->buf, buf->size);

        ret = virtqueue_add_buf(vq, sg, 0, 1, buf);
        virtqueue_kick(vq);
        return ret;
}

/* Discard any unread data this port has. Callers lockers. */
static void discard_port_data(struct port *port)
{
        struct port_buffer *buf;
        struct virtqueue *vq;
        unsigned int len;
        int ret;

        vq = port->in_vq;
        if (port->inbuf)
                buf = port->inbuf;
        else
                buf = virtqueue_get_buf(vq, &len);

        ret = 0;
        while (buf) {
                if (add_inbuf(vq, buf) < 0) {
                        ret++;
                        free_buf(buf);
                }
                buf = virtqueue_get_buf(vq, &len);
        }
        port->inbuf = NULL;
        if (ret)
                dev_warn(port->dev, "Errors adding %d buffers back to vq\n",
                         ret);
}

static bool port_has_data(struct port *port)
{
        unsigned long flags;
        bool ret;

        spin_lock_irqsave(&port->inbuf_lock, flags);
        if (port->inbuf) {
                ret = true;
                goto out;
        }
        port->inbuf = get_inbuf(port);
        if (port->inbuf) {
                ret = true;
                goto out;
        }
        ret = false;
out:
        spin_unlock_irqrestore(&port->inbuf_lock, flags);
        return ret;
}

static ssize_t __send_control_msg(struct ports_device *portdev, u32 port_id,
                                  unsigned int event, unsigned int value)
{
        struct scatterlist sg[1];
        struct virtio_console_control cpkt;
        struct virtqueue *vq;
        unsigned int len;

        if (!use_multiport(portdev))
                return 0;

        cpkt.id = port_id;
        cpkt.event = event;
        cpkt.value = value;

        vq = portdev->c_ovq;

        sg_init_one(sg, &cpkt, sizeof(cpkt));
        if (virtqueue_add_buf(vq, sg, 1, 0, &cpkt) >= 0) {
                virtqueue_kick(vq);
                while (!virtqueue_get_buf(vq, &len))
                        cpu_relax();
        }
        return 0;
}

static ssize_t send_control_msg(struct port *port, unsigned int event,
                                unsigned int value)
{
        /* Did the port get unplugged before userspace closed it? */
        if (port->portdev)
                return __send_control_msg(port->portdev, port->id, event, value);
        return 0;
}

/* Callers must take the port->outvq_lock */
static void reclaim_consumed_buffers(struct port *port)
{
        void *buf;
        unsigned int len;

        while ((buf = virtqueue_get_buf(port->out_vq, &len))) {
                kfree(buf);
                port->outvq_full = false;
        }
}

static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count,
                        bool nonblock)
{
        struct scatterlist sg[1];
        struct virtqueue *out_vq;
        ssize_t ret;
        unsigned long flags;
        unsigned int len;

        out_vq = port->out_vq;

        spin_lock_irqsave(&port->outvq_lock, flags);

        reclaim_consumed_buffers(port);

        sg_init_one(sg, in_buf, in_count);
        ret = virtqueue_add_buf(out_vq, sg, 1, 0, in_buf);

        /* Tell Host to go! */
        virtqueue_kick(out_vq);

        if (ret < 0) {
                in_count = 0;
                goto done;
        }

        if (ret == 0)
                port->outvq_full = true;

        if (nonblock)
                goto done;

        /*
         * Wait till the host acknowledges it pushed out the data we
         * sent.  This is done for data from the hvc_console; the tty
         * operations are performed with spinlocks held so we can't
         * sleep here.  An alternative would be to copy the data to a
         * buffer and relax the spinning requirement.  The downside is
         * we need to kmalloc a GFP_ATOMIC buffer each time the
         * console driver writes something out.
         */
        while (!virtqueue_get_buf(out_vq, &len))
                cpu_relax();
done:
        spin_unlock_irqrestore(&port->outvq_lock, flags);
        /*
         * We're expected to return the amount of data we wrote -- all
         * of it
         */
        return in_count;
}

/*
 * Give out the data that's requested from the buffer that we have
 * queued up.
 */
static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count,
                            bool to_user)
{
        struct port_buffer *buf;
        unsigned long flags;

        if (!out_count || !port_has_data(port))
                return 0;

        buf = port->inbuf;
        out_count = min(out_count, buf->len - buf->offset);

        if (to_user) {
                ssize_t ret;

                ret = copy_to_user(out_buf, buf->buf + buf->offset, out_count);
                if (ret)
                        return -EFAULT;
        } else {
                memcpy(out_buf, buf->buf + buf->offset, out_count);
        }

        buf->offset += out_count;

        if (buf->offset == buf->len) {
                /*
                 * We're done using all the data in this buffer.
                 * Re-queue so that the Host can send us more data.
                 */
                spin_lock_irqsave(&port->inbuf_lock, flags);
                port->inbuf = NULL;

                if (add_inbuf(port->in_vq, buf) < 0)
                        dev_warn(port->dev, "failed add_buf\n");

                spin_unlock_irqrestore(&port->inbuf_lock, flags);
        }
        /* Return the number of bytes actually copied */
        return out_count;
}

/* The condition that must be true for polling to end */
static bool will_read_block(struct port *port)
{
        if (!port->guest_connected) {
                /* Port got hot-unplugged. Let's exit. */
                return false;
        }
        return !port_has_data(port) && port->host_connected;
}

static bool will_write_block(struct port *port)
{
        bool ret;

        if (!port->guest_connected) {
                /* Port got hot-unplugged. Let's exit. */
                return false;
        }
        if (!port->host_connected)
                return true;

        spin_lock_irq(&port->outvq_lock);
        /*
         * Check if the Host has consumed any buffers since we last
         * sent data (this is only applicable for nonblocking ports).
         */
        reclaim_consumed_buffers(port);
        ret = port->outvq_full;
        spin_unlock_irq(&port->outvq_lock);

        return ret;
}

static ssize_t port_fops_read(struct file *filp, char __user *ubuf,
                              size_t count, loff_t *offp)
{
        struct port *port;
        ssize_t ret;

        port = filp->private_data;

        if (!port_has_data(port)) {
                /*
                 * If nothing's connected on the host just return 0 in
                 * case of list_empty; this tells the userspace app
                 * that there's no connection
                 */
                if (!port->host_connected)
                        return 0;
                if (filp->f_flags & O_NONBLOCK)
                        return -EAGAIN;

                ret = wait_event_interruptible(port->waitqueue,
                                               !will_read_block(port));
                if (ret < 0)
                        return ret;
        }
        /* Port got hot-unplugged. */
        if (!port->guest_connected)
                return -ENODEV;
        /*
         * We could've received a disconnection message while we were
         * waiting for more data.
         *
         * This check is not clubbed in the if() statement above as we
         * might receive some data as well as the host could get
         * disconnected after we got woken up from our wait.  So we
         * really want to give off whatever data we have and only then
         * check for host_connected.
         */
        if (!port_has_data(port) && !port->host_connected)
                return 0;

        return fill_readbuf(port, ubuf, count, true);
}

static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
                               size_t count, loff_t *offp)
{
        struct port *port;
        char *buf;
        ssize_t ret;
        bool nonblock;

        /* Userspace could be out to fool us */
        if (!count)
                return 0;

        port = filp->private_data;

        nonblock = filp->f_flags & O_NONBLOCK;

        if (will_write_block(port)) {
                if (nonblock)
                        return -EAGAIN;

                ret = wait_event_interruptible(port->waitqueue,
                                               !will_write_block(port));
                if (ret < 0)
                        return ret;
        }
        /* Port got hot-unplugged. */
        if (!port->guest_connected)
                return -ENODEV;

        count = min((size_t)(32 * 1024), count);

        buf = kmalloc(count, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        ret = copy_from_user(buf, ubuf, count);
        if (ret) {
                ret = -EFAULT;
                goto free_buf;
        }

        /*
         * We now ask send_buf() to not spin for generic ports -- we
         * can re-use the same code path that non-blocking file
         * descriptors take for blocking file descriptors since the
         * wait is already done and we're certain the write will go
         * through to the host.
         */
        nonblock = true;
        ret = send_buf(port, buf, count, nonblock);

        if (nonblock && ret > 0)
                goto out;

free_buf:
        kfree(buf);
out:
        return ret;
}

static unsigned int port_fops_poll(struct file *filp, poll_table *wait)
{
        struct port *port;
        unsigned int ret;

        port = filp->private_data;
        poll_wait(filp, &port->waitqueue, wait);

        if (!port->guest_connected) {
                /* Port got unplugged */
                return POLLHUP;
        }
        ret = 0;
        if (!will_read_block(port))
                ret |= POLLIN | POLLRDNORM;
        if (!will_write_block(port))
                ret |= POLLOUT;
        if (!port->host_connected)
                ret |= POLLHUP;

        return ret;
}

static int port_fops_release(struct inode *inode, struct file *filp)
{
        struct port *port;

        port = filp->private_data;

        /* Notify host of port being closed */
        send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);

        spin_lock_irq(&port->inbuf_lock);
        port->guest_connected = false;

        discard_port_data(port);

        spin_unlock_irq(&port->inbuf_lock);

        spin_lock_irq(&port->outvq_lock);
        reclaim_consumed_buffers(port);
        spin_unlock_irq(&port->outvq_lock);

        return 0;
}

static int port_fops_open(struct inode *inode, struct file *filp)
{
        struct cdev *cdev = inode->i_cdev;
        struct port *port;
        int ret;

        port = container_of(cdev, struct port, cdev);
        filp->private_data = port;

        /*
         * Don't allow opening of console port devices -- that's done
         * via /dev/hvc
         */
        if (is_console_port(port)) {
                ret = -ENXIO;
                goto out;
        }

        /* Allow only one process to open a particular port at a time */
        spin_lock_irq(&port->inbuf_lock);
        if (port->guest_connected) {
                spin_unlock_irq(&port->inbuf_lock);
                ret = -EMFILE;
                goto out;
        }

        port->guest_connected = true;
        spin_unlock_irq(&port->inbuf_lock);

        spin_lock_irq(&port->outvq_lock);
        /*
         * There might be a chance that we missed reclaiming a few
         * buffers in the window of the port getting previously closed
         * and opening now.
         */
        reclaim_consumed_buffers(port);
        spin_unlock_irq(&port->outvq_lock);

        /* Notify host of port being opened */
        send_control_msg(filp->private_data, VIRTIO_CONSOLE_PORT_OPEN, 1);

        return 0;
out:
        return ret;
}

/*
 * The file operations that we support: programs in the guest can open
 * a console device, read from it, write to it, poll for data and
 * close it.  The devices are at
 *   /dev/vport<device number>p<port number>
 */
static const struct file_operations port_fops = {
        .owner = THIS_MODULE,
        .open  = port_fops_open,
        .read  = port_fops_read,
        .write = port_fops_write,
        .poll  = port_fops_poll,
        .release = port_fops_release,
};

/*
 * The put_chars() callback is pretty straightforward.
 *
 * We turn the characters into a scatter-gather list, add it to the
 * output queue and then kick the Host.  Then we sit here waiting for
 * it to finish: inefficient in theory, but in practice
 * implementations will do it immediately (lguest's Launcher does).
 */
static int put_chars(u32 vtermno, const char *buf, int count)
{
        struct port *port;

        if (unlikely(early_put_chars))
                return early_put_chars(vtermno, buf, count);

        port = find_port_by_vtermno(vtermno);
        if (!port)
                return -EPIPE;

        return send_buf(port, (void *)buf, count, false);
}

/*
 * get_chars() is the callback from the hvc_console infrastructure
 * when an interrupt is received.
 *
 * We call out to fill_readbuf that gets us the required data from the
 * buffers that are queued up.
 */
static int get_chars(u32 vtermno, char *buf, int count)
{
        struct port *port;

        /* If we've not set up the port yet, we have no input to give. */
        if (unlikely(early_put_chars))
                return 0;

        port = find_port_by_vtermno(vtermno);
        if (!port)
                return -EPIPE;

        /* If we don't have an input queue yet, we can't get input. */
        BUG_ON(!port->in_vq);

        return fill_readbuf(port, buf, count, false);
}

static void resize_console(struct port *port)
{
        struct virtio_device *vdev;

        /* The port could have been hot-unplugged */
        if (!port || !is_console_port(port))
                return;

        vdev = port->portdev->vdev;
        if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
                hvc_resize(port->cons.hvc, port->cons.ws);
}

/* We set the configuration at this point, since we now have a tty */
static int notifier_add_vio(struct hvc_struct *hp, int data)
{
        struct port *port;

        port = find_port_by_vtermno(hp->vtermno);
        if (!port)
                return -EINVAL;

        hp->irq_requested = 1;
        resize_console(port);

        return 0;
}

static void notifier_del_vio(struct hvc_struct *hp, int data)
{
        hp->irq_requested = 0;
}

/* The operations for console ports. */
static const struct hv_ops hv_ops = {
        .get_chars = get_chars,
        .put_chars = put_chars,
        .notifier_add = notifier_add_vio,
        .notifier_del = notifier_del_vio,
        .notifier_hangup = notifier_del_vio,
};

/*
 * Console drivers are initialized very early so boot messages can go
 * out, so we do things slightly differently from the generic virtio
 * initialization of the net and block drivers.
 *
 * At this stage, the console is output-only.  It's too early to set
 * up a virtqueue, so we let the drivers do some boutique early-output
 * thing.
 */
int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
{
        early_put_chars = put_chars;
        return hvc_instantiate(0, 0, &hv_ops);
}

int init_port_console(struct port *port)
{
        int ret;

        /*
         * The Host's telling us this port is a console port.  Hook it
         * up with an hvc console.
         *
         * To set up and manage our virtual console, we call
         * hvc_alloc().
         *
         * The first argument of hvc_alloc() is the virtual console
         * number.  The second argument is the parameter for the
         * notification mechanism (like irq number).  We currently
         * leave this as zero, virtqueues have implicit notifications.
         *
         * The third argument is a "struct hv_ops" containing the
         * put_chars() get_chars(), notifier_add() and notifier_del()
         * pointers.  The final argument is the output buffer size: we
         * can do any size, so we put PAGE_SIZE here.
         */
        port->cons.vtermno = pdrvdata.next_vtermno;

        port->cons.hvc = hvc_alloc(port->cons.vtermno, 0, &hv_ops, PAGE_SIZE);
        if (IS_ERR(port->cons.hvc)) {
                ret = PTR_ERR(port->cons.hvc);
                dev_err(port->dev,
                        "error %d allocating hvc for port\n", ret);
                port->cons.hvc = NULL;
                return ret;
        }
        spin_lock_irq(&pdrvdata_lock);
        pdrvdata.next_vtermno++;
        list_add_tail(&port->cons.list, &pdrvdata.consoles);
        spin_unlock_irq(&pdrvdata_lock);
        port->guest_connected = true;

        /*
         * Start using the new console output if this is the first
         * console to come up.
         */
        if (early_put_chars)
                early_put_chars = NULL;

        /* Notify host of port being opened */
        send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 1);

        return 0;
}

static ssize_t show_port_name(struct device *dev,
                              struct device_attribute *attr, char *buffer)
{
        struct port *port;

        port = dev_get_drvdata(dev);

        return sprintf(buffer, "%s\n", port->name);
}

static DEVICE_ATTR(name, S_IRUGO, show_port_name, NULL);

static struct attribute *port_sysfs_entries[] = {
        &dev_attr_name.attr,
        NULL
};

static struct attribute_group port_attribute_group = {
        .name = NULL,           /* put in device directory */
        .attrs = port_sysfs_entries,
};

static int debugfs_open(struct inode *inode, struct file *filp)
{
        filp->private_data = inode->i_private;
        return 0;
}

static ssize_t debugfs_read(struct file *filp, char __user *ubuf,
                            size_t count, loff_t *offp)
{
        struct port *port;
        char *buf;
        ssize_t ret, out_offset, out_count;

        out_count = 1024;
        buf = kmalloc(out_count, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        port = filp->private_data;
        out_offset = 0;
        out_offset += snprintf(buf + out_offset, out_count,
                               "name: %s\n", port->name ? port->name : "");
        out_offset += snprintf(buf + out_offset, out_count - out_offset,
                               "guest_connected: %d\n", port->guest_connected);
        out_offset += snprintf(buf + out_offset, out_count - out_offset,
                               "host_connected: %d\n", port->host_connected);
        out_offset += snprintf(buf + out_offset, out_count - out_offset,
                               "outvq_full: %d\n", port->outvq_full);
        out_offset += snprintf(buf + out_offset, out_count - out_offset,
                               "is_console: %s\n",
                               is_console_port(port) ? "yes" : "no");
        out_offset += snprintf(buf + out_offset, out_count - out_offset,
                               "console_vtermno: %u\n", port->cons.vtermno);

        ret = simple_read_from_buffer(ubuf, count, offp, buf, out_offset);
        kfree(buf);
        return ret;
}

static const struct file_operations port_debugfs_ops = {
        .owner = THIS_MODULE,
        .open  = debugfs_open,
        .read  = debugfs_read,
};

static void set_console_size(struct port *port, u16 rows, u16 cols)
{
        if (!port || !is_console_port(port))
                return;

        port->cons.ws.ws_row = rows;
        port->cons.ws.ws_col = cols;
}

static unsigned int fill_queue(struct virtqueue *vq, spinlock_t *lock)
{
        struct port_buffer *buf;
        unsigned int nr_added_bufs;
        int ret;

        nr_added_bufs = 0;
        do {
                buf = alloc_buf(PAGE_SIZE);
                if (!buf)
                        break;

                spin_lock_irq(lock);
                ret = add_inbuf(vq, buf);
                if (ret < 0) {
                        spin_unlock_irq(lock);
                        free_buf(buf);
                        break;
                }
                nr_added_bufs++;
                spin_unlock_irq(lock);
        } while (ret > 0);

        return nr_added_bufs;
}

static int add_port(struct ports_device *portdev, u32 id)
{
        char debugfs_name[16];
        struct port *port;
        struct port_buffer *buf;
        dev_t devt;
        unsigned int nr_added_bufs;
        int err;

        port = kmalloc(sizeof(*port), GFP_KERNEL);
        if (!port) {
                err = -ENOMEM;
                goto fail;
        }

        port->portdev = portdev;
        port->id = id;

        port->name = NULL;
        port->inbuf = NULL;
        port->cons.hvc = NULL;

        port->cons.ws.ws_row = port->cons.ws.ws_col = 0;

        port->host_connected = port->guest_connected = false;

        port->outvq_full = false;

        port->in_vq = portdev->in_vqs[port->id];
        port->out_vq = portdev->out_vqs[port->id];

        cdev_init(&port->cdev, &port_fops);

        devt = MKDEV(portdev->chr_major, id);
        err = cdev_add(&port->cdev, devt, 1);
        if (err < 0) {
                dev_err(&port->portdev->vdev->dev,
                        "Error %d adding cdev for port %u\n", err, id);
                goto free_port;
        }
        port->dev = device_create(pdrvdata.class, &port->portdev->vdev->dev,
                                  devt, port, "vport%up%u",
                                  port->portdev->drv_index, id);
        if (IS_ERR(port->dev)) {
                err = PTR_ERR(port->dev);
                dev_err(&port->portdev->vdev->dev,
                        "Error %d creating device for port %u\n",
                        err, id);
                goto free_cdev;
        }

        spin_lock_init(&port->inbuf_lock);
        spin_lock_init(&port->outvq_lock);
        init_waitqueue_head(&port->waitqueue);

        /* Fill the in_vq with buffers so the host can send us data. */
        nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
        if (!nr_added_bufs) {
                dev_err(port->dev, "Error allocating inbufs\n");
                err = -ENOMEM;
                goto free_device;
        }

        /*
         * If we're not using multiport support, this has to be a console port
         */
        if (!use_multiport(port->portdev)) {
                err = init_port_console(port);
                if (err)
                        goto free_inbufs;
        }

        spin_lock_irq(&portdev->ports_lock);
        list_add_tail(&port->list, &port->portdev->ports);
        spin_unlock_irq(&portdev->ports_lock);

        /*
         * Tell the Host we're set so that it can send us various
         * configuration parameters for this port (eg, port name,
         * caching, whether this is a console port, etc.)
         */
        send_control_msg(port, VIRTIO_CONSOLE_PORT_READY, 1);

        if (pdrvdata.debugfs_dir) {
                /*
                 * Finally, create the debugfs file that we can use to
                 * inspect a port's state at any time
                 */
                sprintf(debugfs_name, "vport%up%u",
                        port->portdev->drv_index, id);
                port->debugfs_file = debugfs_create_file(debugfs_name, 0444,
                                                         pdrvdata.debugfs_dir,
                                                         port,
                                                         &port_debugfs_ops);
        }
        return 0;

free_inbufs:
        while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
                free_buf(buf);
free_device:
        device_destroy(pdrvdata.class, port->dev->devt);
free_cdev:
        cdev_del(&port->cdev);
free_port:
        kfree(port);
fail:
        /* The host might want to notify management sw about port add failure */
        __send_control_msg(portdev, id, VIRTIO_CONSOLE_PORT_READY, 0);
        return err;
}

/* Remove all port-specific data. */
static void remove_port(struct port *port)
{
        struct port_buffer *buf;

        if (port->guest_connected) {
                port->guest_connected = false;
                port->host_connected = false;
                wake_up_interruptible(&port->waitqueue);
                send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
        }

        spin_lock_irq(&port->portdev->ports_lock);
        list_del(&port->list);
        spin_unlock_irq(&port->portdev->ports_lock);

        if (is_console_port(port)) {
                spin_lock_irq(&pdrvdata_lock);
                list_del(&port->cons.list);
                spin_unlock_irq(&pdrvdata_lock);
#if 0
                /*
                 * hvc_remove() not called as removing one hvc port
                 * results in other hvc ports getting frozen.
                 *
                 * Once this is resolved in hvc, this functionality
                 * will be enabled.  Till that is done, the -EPIPE
                 * return from get_chars() above will help
                 * hvc_console.c to clean up on ports we remove here.
                 */
                hvc_remove(port->cons.hvc);
#endif
        }
        sysfs_remove_group(&port->dev->kobj, &port_attribute_group);
        device_destroy(pdrvdata.class, port->dev->devt);
        cdev_del(&port->cdev);

        /* Remove unused data this port might have received. */
        discard_port_data(port);

        reclaim_consumed_buffers(port);

        /* Remove buffers we queued up for the Host to send us data in. */
        while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
                free_buf(buf);

        kfree(port->name);

        debugfs_remove(port->debugfs_file);

        kfree(port);
}

/* Any private messages that the Host and Guest want to share */
static void handle_control_message(struct ports_device *portdev,
                                   struct port_buffer *buf)
{
        struct virtio_console_control *cpkt;
        struct port *port;
        size_t name_size;
        int err;

        cpkt = (struct virtio_console_control *)(buf->buf + buf->offset);

        port = find_port_by_id(portdev, cpkt->id);
        if (!port && cpkt->event != VIRTIO_CONSOLE_PORT_ADD) {
                /* No valid header at start of buffer.  Drop it. */
                dev_dbg(&portdev->vdev->dev,
                        "Invalid index %u in control packet\n", cpkt->id);
                return;
        }

        switch (cpkt->event) {
        case VIRTIO_CONSOLE_PORT_ADD:
                if (port) {
                        dev_dbg(&portdev->vdev->dev,
                                "Port %u already added\n", port->id);
                        send_control_msg(port, VIRTIO_CONSOLE_PORT_READY, 1);
                        break;
                }
                if (cpkt->id >= portdev->config.max_nr_ports) {
                        dev_warn(&portdev->vdev->dev,
                                "Request for adding port with out-of-bound id %u, max. supported id: %u\n",
                                cpkt->id, portdev->config.max_nr_ports - 1);
                        break;
                }
                add_port(portdev, cpkt->id);
                break;
        case VIRTIO_CONSOLE_PORT_REMOVE:
                remove_port(port);
                break;
        case VIRTIO_CONSOLE_CONSOLE_PORT:
                if (!cpkt->value)
                        break;
                if (is_console_port(port))
                        break;

                init_port_console(port);
                /*
                 * Could remove the port here in case init fails - but
                 * have to notify the host first.
                 */
                break;
        case VIRTIO_CONSOLE_RESIZE: {
                struct {
                        __u16 rows;
                        __u16 cols;
                } size;

                if (!is_console_port(port))
                        break;

                memcpy(&size, buf->buf + buf->offset + sizeof(*cpkt),
                       sizeof(size));
                set_console_size(port, size.rows, size.cols);

                port->cons.hvc->irq_requested = 1;
                resize_console(port);
                break;
        }
        case VIRTIO_CONSOLE_PORT_OPEN:
                port->host_connected = cpkt->value;
                wake_up_interruptible(&port->waitqueue);
                /*
                 * If the host port got closed and the host had any
                 * unconsumed buffers, we'll be able to reclaim them
                 * now.
                 */
                spin_lock_irq(&port->outvq_lock);
                reclaim_consumed_buffers(port);
                spin_unlock_irq(&port->outvq_lock);
                break;
        case VIRTIO_CONSOLE_PORT_NAME:
                /*
                 * Skip the size of the header and the cpkt to get the size
                 * of the name that was sent
                 */
                name_size = buf->len - buf->offset - sizeof(*cpkt) + 1;

                port->name = kmalloc(name_size, GFP_KERNEL);
                if (!port->name) {
                        dev_err(port->dev,
                                "Not enough space to store port name\n");
                        break;
                }
                strncpy(port->name, buf->buf + buf->offset + sizeof(*cpkt),
                        name_size - 1);
                port->name[name_size - 1] = 0;

                /*
                 * Since we only have one sysfs attribute, 'name',
                 * create it only if we have a name for the port.
                 */
                err = sysfs_create_group(&port->dev->kobj,
                                         &port_attribute_group);
                if (err) {
                        dev_err(port->dev,
                                "Error %d creating sysfs device attributes\n",
                                err);
                } else {
                        /*
                         * Generate a udev event so that appropriate
                         * symlinks can be created based on udev
                         * rules.
                         */
                        kobject_uevent(&port->dev->kobj, KOBJ_CHANGE);
                }
                break;
        }
}

static void control_work_handler(struct work_struct *work)
{
        struct ports_device *portdev;
        struct virtqueue *vq;
        struct port_buffer *buf;
        unsigned int len;

        portdev = container_of(work, struct ports_device, control_work);
        vq = portdev->c_ivq;

        spin_lock(&portdev->cvq_lock);
        while ((buf = virtqueue_get_buf(vq, &len))) {
                spin_unlock(&portdev->cvq_lock);

                buf->len = len;
                buf->offset = 0;

                handle_control_message(portdev, buf);

                spin_lock(&portdev->cvq_lock);
                if (add_inbuf(portdev->c_ivq, buf) < 0) {
                        dev_warn(&portdev->vdev->dev,
                                 "Error adding buffer to queue\n");
                        free_buf(buf);
                }
        }
        spin_unlock(&portdev->cvq_lock);
}

static void in_intr(struct virtqueue *vq)
{
        struct port *port;
        unsigned long flags;

        port = find_port_by_vq(vq->vdev->priv, vq);
        if (!port)
                return;

        spin_lock_irqsave(&port->inbuf_lock, flags);
        if (!port->inbuf)
                port->inbuf = get_inbuf(port);

        /*
         * Don't queue up data when port is closed.  This condition
         * can be reached when a console port is not yet connected (no
         * tty is spawned) and the host sends out data to console
         * ports.  For generic serial ports, the host won't
         * (shouldn't) send data till the guest is connected.
         */
        if (!port->guest_connected)
                discard_port_data(port);

        spin_unlock_irqrestore(&port->inbuf_lock, flags);

        wake_up_interruptible(&port->waitqueue);

        if (is_console_port(port) && hvc_poll(port->cons.hvc))
                hvc_kick();
}

static void control_intr(struct virtqueue *vq)
{
        struct ports_device *portdev;

        portdev = vq->vdev->priv;
        schedule_work(&portdev->control_work);
}

static void config_intr(struct virtio_device *vdev)
{
        struct ports_device *portdev;

        portdev = vdev->priv;

        if (!use_multiport(portdev)) {
                struct port *port;
                u16 rows, cols;

                vdev->config->get(vdev,
                                  offsetof(struct virtio_console_config, cols),
                                  &cols, sizeof(u16));
                vdev->config->get(vdev,
                                  offsetof(struct virtio_console_config, rows),
                                  &rows, sizeof(u16));

                port = find_port_by_id(portdev, 0);
                set_console_size(port, rows, cols);

                /*
                 * We'll use this way of resizing only for legacy
                 * support.  For newer userspace
                 * (VIRTIO_CONSOLE_F_MULTPORT+), use control messages
                 * to indicate console size changes so that it can be
                 * done per-port.
                 */
                resize_console(port);
        }
}

static int init_vqs(struct ports_device *portdev)
{
        vq_callback_t **io_callbacks;
        char **io_names;
        struct virtqueue **vqs;
        u32 i, j, nr_ports, nr_queues;
        int err;

        nr_ports = portdev->config.max_nr_ports;
        nr_queues = use_multiport(portdev) ? (nr_ports + 1) * 2 : 2;

        vqs = kmalloc(nr_queues * sizeof(struct virtqueue *), GFP_KERNEL);
        if (!vqs) {
                err = -ENOMEM;
                goto fail;
        }
        io_callbacks = kmalloc(nr_queues * sizeof(vq_callback_t *), GFP_KERNEL);
        if (!io_callbacks) {
                err = -ENOMEM;
                goto free_vqs;
        }
        io_names = kmalloc(nr_queues * sizeof(char *), GFP_KERNEL);
        if (!io_names) {
                err = -ENOMEM;
                goto free_callbacks;
        }
        portdev->in_vqs = kmalloc(nr_ports * sizeof(struct virtqueue *),
                                  GFP_KERNEL);
        if (!portdev->in_vqs) {
                err = -ENOMEM;
                goto free_names;
        }
        portdev->out_vqs = kmalloc(nr_ports * sizeof(struct virtqueue *),
                                   GFP_KERNEL);
        if (!portdev->out_vqs) {
                err = -ENOMEM;
                goto free_invqs;
        }

        /*
         * For backward compat (newer host but older guest), the host
         * spawns a console port first and also inits the vqs for port
         * 0 before others.
         */
        j = 0;
        io_callbacks[j] = in_intr;
        io_callbacks[j + 1] = NULL;
        io_names[j] = "input";
        io_names[j + 1] = "output";
        j += 2;

        if (use_multiport(portdev)) {
                io_callbacks[j] = control_intr;
                io_callbacks[j + 1] = NULL;
                io_names[j] = "control-i";
                io_names[j + 1] = "control-o";

                for (i = 1; i < nr_ports; i++) {
                        j += 2;
                        io_callbacks[j] = in_intr;
                        io_callbacks[j + 1] = NULL;
                        io_names[j] = "input";
                        io_names[j + 1] = "output";
                }
        }
        /* Find the queues. */
        err = portdev->vdev->config->find_vqs(portdev->vdev, nr_queues, vqs,
                                              io_callbacks,
                                              (const char **)io_names);
        if (err)
                goto free_outvqs;

        j = 0;
        portdev->in_vqs[0] = vqs[0];
        portdev->out_vqs[0] = vqs[1];
        j += 2;
        if (use_multiport(portdev)) {
                portdev->c_ivq = vqs[j];
                portdev->c_ovq = vqs[j + 1];

                for (i = 1; i < nr_ports; i++) {
                        j += 2;
                        portdev->in_vqs[i] = vqs[j];
                        portdev->out_vqs[i] = vqs[j + 1];
                }
        }
        kfree(io_callbacks);
        kfree(io_names);
        kfree(vqs);

        return 0;

free_names:
        kfree(io_names);
free_callbacks:
        kfree(io_callbacks);
free_outvqs:
        kfree(portdev->out_vqs);
free_invqs:
        kfree(portdev->in_vqs);
free_vqs:
        kfree(vqs);
fail:
        return err;
}

static const struct file_operations portdev_fops = {
        .owner = THIS_MODULE,
};

/*
 * Once we're further in boot, we get probed like any other virtio
 * device.
 *
 * If the host also supports multiple console ports, we check the
 * config space to see how many ports the host has spawned.  We
 * initialize each port found.
 */
static int __devinit virtcons_probe(struct virtio_device *vdev)
{
        struct ports_device *portdev;
        int err;
        bool multiport;

        portdev = kmalloc(sizeof(*portdev), GFP_KERNEL);
        if (!portdev) {
                err = -ENOMEM;
                goto fail;
        }

        /* Attach this portdev to this virtio_device, and vice-versa. */
        portdev->vdev = vdev;
        vdev->priv = portdev;

        spin_lock_irq(&pdrvdata_lock);
        portdev->drv_index = pdrvdata.index++;
        spin_unlock_irq(&pdrvdata_lock);

        portdev->chr_major = register_chrdev(0, "virtio-portsdev",
                                             &portdev_fops);
        if (portdev->chr_major < 0) {
                dev_err(&vdev->dev,
                        "Error %d registering chrdev for device %u\n",
                        portdev->chr_major, portdev->drv_index);
                err = portdev->chr_major;
                goto free;
        }

        multiport = false;
        portdev->config.max_nr_ports = 1;
        if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT)) {
                multiport = true;
                vdev->features[0] |= 1 << VIRTIO_CONSOLE_F_MULTIPORT;

                vdev->config->get(vdev, offsetof(struct virtio_console_config,
                                                 max_nr_ports),
                                  &portdev->config.max_nr_ports,
                                  sizeof(portdev->config.max_nr_ports));
        }

        /* Let the Host know we support multiple ports.*/
        vdev->config->finalize_features(vdev);

        err = init_vqs(portdev);
        if (err < 0) {
                dev_err(&vdev->dev, "Error %d initializing vqs\n", err);
                goto free_chrdev;
        }

        spin_lock_init(&portdev->ports_lock);
        INIT_LIST_HEAD(&portdev->ports);

        if (multiport) {
                unsigned int nr_added_bufs;

                spin_lock_init(&portdev->cvq_lock);
                INIT_WORK(&portdev->control_work, &control_work_handler);

                nr_added_bufs = fill_queue(portdev->c_ivq, &portdev->cvq_lock);
                if (!nr_added_bufs) {
                        dev_err(&vdev->dev,
                                "Error allocating buffers for control queue\n");
                        err = -ENOMEM;
                        goto free_vqs;
                }
        } else {
                /*
                 * For backward compatibility: Create a console port
                 * if we're running on older host.
                 */
                add_port(portdev, 0);
        }

        __send_control_msg(portdev, VIRTIO_CONSOLE_BAD_ID,
                           VIRTIO_CONSOLE_DEVICE_READY, 1);
        return 0;

free_vqs:
        /* The host might want to notify mgmt sw about device add failure */
        __send_control_msg(portdev, VIRTIO_CONSOLE_BAD_ID,
                           VIRTIO_CONSOLE_DEVICE_READY, 0);
        vdev->config->del_vqs(vdev);
        kfree(portdev->in_vqs);
        kfree(portdev->out_vqs);
free_chrdev:
        unregister_chrdev(portdev->chr_major, "virtio-portsdev");
free:
        kfree(portdev);
fail:
        return err;
}

static void virtcons_remove(struct virtio_device *vdev)
{
        struct ports_device *portdev;
        struct port *port, *port2;

        portdev = vdev->priv;

        /* Disable interrupts for vqs */
        vdev->config->reset(vdev);
        /* Finish up work that's lined up */
        cancel_work_sync(&portdev->control_work);

        list_for_each_entry_safe(port, port2, &portdev->ports, list)
                remove_port(port);

        unregister_chrdev(portdev->chr_major, "virtio-portsdev");

        if (use_multiport(portdev)) {
                struct port_buffer *buf;
                unsigned int len;

                while ((buf = virtqueue_get_buf(portdev->c_ivq, &len)))
                        free_buf(buf);

                while ((buf = virtqueue_detach_unused_buf(portdev->c_ivq)))
                        free_buf(buf);
        }

        vdev->config->del_vqs(vdev);
        kfree(portdev->in_vqs);
        kfree(portdev->out_vqs);

        kfree(portdev);
}

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

static unsigned int features[] = {
        VIRTIO_CONSOLE_F_SIZE,
        VIRTIO_CONSOLE_F_MULTIPORT,
};

static struct virtio_driver virtio_console = {
        .feature_table = features,
        .feature_table_size = ARRAY_SIZE(features),
        .driver.name =  KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table =     id_table,
        .probe =        virtcons_probe,
        .remove =       virtcons_remove,
        .config_changed = config_intr,
};

static int __init init(void)
{
        int err;

        pdrvdata.class = class_create(THIS_MODULE, "virtio-ports");
        if (IS_ERR(pdrvdata.class)) {
                err = PTR_ERR(pdrvdata.class);
                pr_err("Error %d creating virtio-ports class\n", err);
                return err;
        }

        pdrvdata.debugfs_dir = debugfs_create_dir("virtio-ports", NULL);
        if (!pdrvdata.debugfs_dir) {
                pr_warning("Error %ld creating debugfs dir for virtio-ports\n",
                           PTR_ERR(pdrvdata.debugfs_dir));
        }
        INIT_LIST_HEAD(&pdrvdata.consoles);

        return register_virtio_driver(&virtio_console);
}

static void __exit fini(void)
{
        unregister_virtio_driver(&virtio_console);

        class_destroy(pdrvdata.class);
        if (pdrvdata.debugfs_dir)
                debugfs_remove_recursive(pdrvdata.debugfs_dir);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio console driver");
MODULE_LICENSE("GPL");