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-rw-r--r--drivers/char/virtio_console.c225
1 files changed, 225 insertions, 0 deletions
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
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1/*D:300
2 * The Guest console driver
3 *
4 * Writing console drivers is one of the few remaining Dark Arts in Linux.
5 * Fortunately for us, the path of virtual consoles has been well-trodden by
6 * the PowerPC folks, who wrote "hvc_console.c" to generically support any
7 * virtual console. We use that infrastructure which only requires us to write
8 * the basic put_chars and get_chars functions and call the right register
9 * functions.
10 :*/
11
12/*M:002 The console can be flooded: while the Guest is processing input the
13 * Host can send more. Buffering in the Host could alleviate this, but it is a
14 * difficult problem in general. :*/
15/* Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
16 *
17 * This program is free software; you can redistribute it and/or modify
18 * it under the terms of the GNU General Public License as published by
19 * the Free Software Foundation; either version 2 of the License, or
20 * (at your option) any later version.
21 *
22 * This program is distributed in the hope that it will be useful,
23 * but WITHOUT ANY WARRANTY; without even the implied warranty of
24 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
25 * GNU General Public License for more details.
26 *
27 * You should have received a copy of the GNU General Public License
28 * along with this program; if not, write to the Free Software
29 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
30 */
31#include <linux/err.h>
32#include <linux/init.h>
33#include <linux/virtio.h>
34#include <linux/virtio_console.h>
35#include "hvc_console.h"
36
37/*D:340 These represent our input and output console queues, and the virtio
38 * operations for them. */
39static struct virtqueue *in_vq, *out_vq;
40static struct virtio_device *vdev;
41
42/* This is our input buffer, and how much data is left in it. */
43static unsigned int in_len;
44static char *in, *inbuf;
45
46/* The operations for our console. */
47static struct hv_ops virtio_cons;
48
49/*D:310 The put_chars() callback is pretty straightforward.
50 *
51 * We turn the characters into a scatter-gather list, add it to the output
52 * queue and then kick the Host. Then we sit here waiting for it to finish:
53 * inefficient in theory, but in practice implementations will do it
54 * immediately (lguest's Launcher does). */
55static int put_chars(u32 vtermno, const char *buf, int count)
56{
57 struct scatterlist sg[1];
58 unsigned int len;
59
60 /* This is a convenient routine to initialize a single-elem sg list */
61 sg_init_one(sg, buf, count);
62
63 /* add_buf wants a token to identify this buffer: we hand it any
64 * non-NULL pointer, since there's only ever one buffer. */
65 if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
66 /* Tell Host to go! */
67 out_vq->vq_ops->kick(out_vq);
68 /* Chill out until it's done with the buffer. */
69 while (!out_vq->vq_ops->get_buf(out_vq, &len))
70 cpu_relax();
71 }
72
73 /* We're expected to return the amount of data we wrote: all of it. */
74 return count;
75}
76
77/* Create a scatter-gather list representing our input buffer and put it in the
78 * queue. */
79static void add_inbuf(void)
80{
81 struct scatterlist sg[1];
82 sg_init_one(sg, inbuf, PAGE_SIZE);
83
84 /* We should always be able to add one buffer to an empty queue. */
85 if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)
86 BUG();
87 in_vq->vq_ops->kick(in_vq);
88}
89
90/*D:350 get_chars() is the callback from the hvc_console infrastructure when
91 * an interrupt is received.
92 *
93 * Most of the code deals with the fact that the hvc_console() infrastructure
94 * only asks us for 16 bytes at a time. We keep in_offset and in_used fields
95 * for partially-filled buffers. */
96static int get_chars(u32 vtermno, char *buf, int count)
97{
98 /* If we don't have an input queue yet, we can't get input. */
99 BUG_ON(!in_vq);
100
101 /* No buffer? Try to get one. */
102 if (!in_len) {
103 in = in_vq->vq_ops->get_buf(in_vq, &in_len);
104 if (!in)
105 return 0;
106 }
107
108 /* You want more than we have to give? Well, try wanting less! */
109 if (in_len < count)
110 count = in_len;
111
112 /* Copy across to their buffer and increment offset. */
113 memcpy(buf, in, count);
114 in += count;
115 in_len -= count;
116
117 /* Finished? Re-register buffer so Host will use it again. */
118 if (in_len == 0)
119 add_inbuf();
120
121 return count;
122}
123/*:*/
124
125/*D:320 Console drivers are initialized very early so boot messages can go out,
126 * so we do things slightly differently from the generic virtio initialization
127 * of the net and block drivers.
128 *
129 * At this stage, the console is output-only. It's too early to set up a
130 * virtqueue, so we let the drivers do some boutique early-output thing. */
131int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
132{
133 virtio_cons.put_chars = put_chars;
134 return hvc_instantiate(0, 0, &virtio_cons);
135}
136
137/*D:370 Once we're further in boot, we get probed like any other virtio device.
138 * At this stage we set up the output virtqueue.
139 *
140 * To set up and manage our virtual console, we call hvc_alloc(). Since we
141 * never remove the console device we never need this pointer again.
142 *
143 * Finally we put our input buffer in the input queue, ready to receive. */
144static int virtcons_probe(struct virtio_device *dev)
145{
146 int err;
147 struct hvc_struct *hvc;
148
149 vdev = dev;
150
151 /* This is the scratch page we use to receive console input */
152 inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
153 if (!inbuf) {
154 err = -ENOMEM;
155 goto fail;
156 }
157
158 /* Find the input queue. */
159 /* FIXME: This is why we want to wean off hvc: we do nothing
160 * when input comes in. */
161 in_vq = vdev->config->find_vq(vdev, NULL);
162 if (IS_ERR(in_vq)) {
163 err = PTR_ERR(in_vq);
164 goto free;
165 }
166
167 out_vq = vdev->config->find_vq(vdev, NULL);
168 if (IS_ERR(out_vq)) {
169 err = PTR_ERR(out_vq);
170 goto free_in_vq;
171 }
172
173 /* Start using the new console output. */
174 virtio_cons.get_chars = get_chars;
175 virtio_cons.put_chars = put_chars;
176
177 /* The first argument of hvc_alloc() is the virtual console number, so
178 * we use zero. The second argument is the interrupt number; we
179 * currently leave this as zero: it would be better not to use the
180 * hvc mechanism and fix this (FIXME!).
181 *
182 * The third argument is a "struct hv_ops" containing the put_chars()
183 * and get_chars() pointers. The final argument is the output buffer
184 * size: we can do any size, so we put PAGE_SIZE here. */
185 hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);
186 if (IS_ERR(hvc)) {
187 err = PTR_ERR(hvc);
188 goto free_out_vq;
189 }
190
191 /* Register the input buffer the first time. */
192 add_inbuf();
193 return 0;
194
195free_out_vq:
196 vdev->config->del_vq(out_vq);
197free_in_vq:
198 vdev->config->del_vq(in_vq);
199free:
200 kfree(inbuf);
201fail:
202 return err;
203}
204
205static struct virtio_device_id id_table[] = {
206 { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
207 { 0 },
208};
209
210static struct virtio_driver virtio_console = {
211 .driver.name = KBUILD_MODNAME,
212 .driver.owner = THIS_MODULE,
213 .id_table = id_table,
214 .probe = virtcons_probe,
215};
216
217static int __init init(void)
218{
219 return register_virtio_driver(&virtio_console);
220}
221module_init(init);
222
223MODULE_DEVICE_TABLE(virtio, id_table);
224MODULE_DESCRIPTION("Virtio console driver");
225MODULE_LICENSE("GPL");
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