blob: dc17fe3a88bc48f2813ad5c3e5dd27efd00ff7d3 [file] [log] [blame]
* 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
* 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! */
/* Chill out until it's done with the buffer. */
while (!out_vq->vq_ops->get_buf(out_vq, &len))
/* 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)
/*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. */
/* 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)
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, 0, NULL);
if (IS_ERR(in_vq)) {
err = PTR_ERR(in_vq);
goto free;
out_vq = vdev->config->find_vq(vdev, 1, 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. */
return 0;
return err;
static struct virtio_device_id id_table[] = {
{ 0 },
static struct virtio_driver virtio_console = { = 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_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio console driver");