virtio: console: comment cleanup

/*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

/*

 * Copyright (C) 2006, 2007, 2009 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

#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;

/* The hvc device */

static struct hvc_struct *hvc;

/*D:310 The put_chars() callback is pretty straightforward.

/*

 * 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). */

 * 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];

	/* 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. */

	/*

	 * 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);

	return count;

}

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

 * queue. */

/*

 * Create a scatter-gather list representing our input buffer and put

 * it in the queue.

 */

static void add_inbuf(void)

{

	struct scatterlist sg[1];

	in_vq->vq_ops->kick(in_vq);

}

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

 * an interrupt is received.

/*

 * 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. */

 * 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. */

	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.

/*

 * 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. */

 * 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;

}

/*

 * we support only one console, the hvc struct is a global var

 * We set the configuration at this point, since we now have a tty

 * we support only one console, the hvc struct is a global var We set

 * the configuration at this point, since we now have a tty

 */

static int notifier_add_vio(struct hvc_struct *hp, int data)

{

		hvc_kick();

}

/*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.

/*

 * 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.

 * 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. */

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

 * receive.

 */

static int __devinit virtcons_probe(struct virtio_device *dev)

{

	vq_callback_t *callbacks[] = { hvc_handle_input, NULL};

	}

	/* Find the queues. */

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

	 * when input comes in. */

	err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);

	if (err)

		goto free;

	virtio_cons.notifier_del = notifier_del_vio;

	virtio_cons.notifier_hangup = notifier_del_vio;

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

	 * we use zero.  The second argument is the parameter for the

	 * notification mechanism (like irq number). We currently leave this

	 * as zero, virtqueues have implicit notifications.

	/*

	 * The first argument of hvc_alloc() is the virtual console

	 * number, so we use zero.  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. */

	 * 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.

	 */

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

	if (IS_ERR(hvc)) {

		err = PTR_ERR(hvc);

#include <linux/types.h>

#include <linux/virtio_ids.h>

#include <linux/virtio_config.h>

/* This header, excluding the #ifdef __KERNEL__ part, is BSD licensed so

 * anyone can use the definitions to implement compatible drivers/servers. */

/*

 * This header, excluding the #ifdef __KERNEL__ part, is BSD licensed so

 * anyone can use the definitions to implement compatible drivers/servers.

 */

/* Feature bits */

#define VIRTIO_CONSOLE_F_SIZE	0	/* Does host provide console size? */