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/*D:300

 * The Guest console driver

 *

 * Writing console drivers is one of the few remaining Dark Arts in Linux.

 * Fortunately for us, the path of virtual consoles has been well-trodden by

 * the PowerPC folks, who wrote "hvc_console.c" to generically support any

 * virtual console.  We use that infrastructure which only requires us to write

 * the basic put_chars and get_chars functions and call the right register

 * functions.

 :*/

/*M:002 The console can be flooded: while the Guest is processing input the

 * Host can send more.  Buffering in the Host could alleviate this, but it is a

 * difficult problem in general. :*/

/* 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 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/err.h>

#include <linux/init.h>

#include <linux/virtio.h>

#include <linux/virtio_console.h>

#include "hvc_console.h"

/*D:340 These represent our input and output console queues, and the virtio

 * operations for them. */

static struct virtqueue *in_vq, *out_vq;

static struct virtio_device *vdev;

/* This is our input buffer, and how much data is left in it. */

static unsigned int in_len;

static char *in, *inbuf;

/* The operations for our console. */

static struct hv_ops virtio_cons;

/*D:310 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 scatterlist sg[1];

        unsigned int len;

        /* This is a convenient routine to initialize a single-elem sg list */

        sg_init_one(sg, buf, count);

        /* add_buf wants a token to identify this buffer: we hand it any

         * non-NULL pointer, since there's only ever one buffer. */

        if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {

                /* Tell Host to go! */

                out_vq->vq_ops->kick(out_vq);

                /* Chill out until it's done with the buffer. */

                while (!out_vq->vq_ops->get_buf(out_vq, &len))

                        cpu_relax();

        }

        /* We're expected to return the amount of data we wrote: all of it. */

        return count;

}

/* Create a scatter-gather list representing our input buffer and put it in the

 * queue. */

static void add_inbuf(void)

{

        struct scatterlist sg[1];

        sg_init_one(sg, inbuf, PAGE_SIZE);

        /* We should always be able to add one buffer to an empty queue. */

        if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)

                BUG();

        in_vq->vq_ops->kick(in_vq);

}

/*D:350 get_chars() is the callback from the hvc_console infrastructure when

 * an interrupt is received.

 *

 * Most of the code deals with the fact that the hvc_console() infrastructure

 * only asks us for 16 bytes at a time.  We keep in_offset and in_used fields

 * for partially-filled buffers. */

static int get_chars(u32 vtermno, char *buf, int count)

{

        /* If we don't have an input queue yet, we can't get input. */

        BUG_ON(!in_vq);

        /* No buffer?  Try to get one. */

        if (!in_len) {

                in = in_vq->vq_ops->get_buf(in_vq, &in_len);

                if (!in)

                        return 0;

        }

        /* You want more than we have to give?  Well, try wanting less! */

        if (in_len < count)

                count = in_len;

        /* Copy across to their buffer and increment offset. */

        memcpy(buf, in, count);

        in += count;

        in_len -= count;

        /* Finished?  Re-register buffer so Host will use it again. */

        if (in_len == 0)

                add_inbuf();

        return count;

}

/*:*/

/*D:320 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))

{

        virtio_cons.put_chars = put_chars;

        return hvc_instantiate(0, 0, &virtio_cons);

}

/*D:370 Once we're further in boot, we get probed like any other virtio device.

 * At this stage we set up the output virtqueue.

 *

 * To set up and manage our virtual console, we call hvc_alloc().  Since we

 * never remove the console device we never need this pointer again.

 *

 * Finally we put our input buffer in the input queue, ready to receive. */

static int __devinit virtcons_probe(struct virtio_device *dev)

{

        int err;

        struct hvc_struct *hvc;

        vdev = dev;

        /* This is the scratch page we use to receive console input */

        inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);

        if (!inbuf) {

                err = -ENOMEM;

                goto fail;

        }

        /* Find the input queue. */

        /* FIXME: This is why we want to wean off hvc: we do nothing

         * when input comes in. */

        in_vq = vdev->config->find_vq(vdev, NULL);

        if (IS_ERR(in_vq)) {

                err = PTR_ERR(in_vq);

                goto free;

        }

        out_vq = vdev->config->find_vq(vdev, NULL);

        if (IS_ERR(out_vq)) {

                err = PTR_ERR(out_vq);

                goto free_in_vq;

        }

        /* Start using the new console output. */

        virtio_cons.get_chars = get_chars;

        virtio_cons.put_chars = put_chars;

        /* The first argument of hvc_alloc() is the virtual console number, so

         * we use zero.  The second argument is the interrupt number; we

         * currently leave this as zero: it would be better not to use the

         * hvc mechanism and fix this (FIXME!).

         *

         * The third argument is a "struct hv_ops" containing the put_chars()

         * and get_chars() pointers.  The final argument is the output buffer

         * size: we can do any size, so we put PAGE_SIZE here. */

        hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);

        if (IS_ERR(hvc)) {

                err = PTR_ERR(hvc);

                goto free_out_vq;

        }

        /* Register the input buffer the first time. */

        add_inbuf();

        return 0;

free_out_vq:

        vdev->config->del_vq(out_vq);

free_in_vq:

        vdev->config->del_vq(in_vq);

free:

        kfree(inbuf);

fail:

        return err;

}

static struct virtio_device_id id_table[] = {

        { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },

        { 0 },

};

static struct virtio_driver virtio_console = {

        .driver.name =  KBUILD_MODNAME,

        .driver.owner = THIS_MODULE,

        .id_table =     id_table,

        .probe =        virtcons_probe,

};

static int __init init(void)

{

        return register_virtio_driver(&virtio_console);

}

module_init(init);

MODULE_DEVICE_TABLE(virtio, id_table);

MODULE_DESCRIPTION("Virtio console driver");

MODULE_LICENSE("GPL");