drivers/char/virtio_console.c

   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_ids.h>
  35 #include <linux/virtio_console.h>
  36 #include "hvc_console.h"
  37
  38 /*D:340 These represent our input and output console queues, and the virtio
  39  * operations for them. */
  40 static struct virtqueue *in_vq, *out_vq;
  41 static struct virtio_device *vdev;
  42
  43 /* This is our input buffer, and how much data is left in it. */
  44 static unsigned int in_len;
  45 static char *in, *inbuf;
  46
  47 /* The operations for our console. */
  48 static struct hv_ops virtio_cons;
  49
  50 /* The hvc device */
  51 static struct hvc_struct *hvc;
  52
  53 /*D:310 The put_chars() callback is pretty straightforward.
  54  *
  55  * We turn the characters into a scatter-gather list, add it to the output
  56  * queue and then kick the Host.  Then we sit here waiting for it to finish:
  57  * inefficient in theory, but in practice implementations will do it
  58  * immediately (lguest's Launcher does). */
  59 static int put_chars(u32 vtermno, const char *buf, int count)
  60 {
  61         struct scatterlist sg[1];
  62         unsigned int len;
  63
  64         /* This is a convenient routine to initialize a single-elem sg list */
  65         sg_init_one(sg, buf, count);
  66
  67         /* add_buf wants a token to identify this buffer: we hand it any
  68          * non-NULL pointer, since there's only ever one buffer. */
  69         if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) >= 0) {
  70                 /* Tell Host to go! */
  71                 out_vq->vq_ops->kick(out_vq);
  72                 /* Chill out until it's done with the buffer. */
  73                 while (!out_vq->vq_ops->get_buf(out_vq, &len))
  74                         cpu_relax();
  75         }
  76
  77         /* We're expected to return the amount of data we wrote: all of it. */
  78         return count;
  79 }
  80
  81 /* Create a scatter-gather list representing our input buffer and put it in the
  82  * queue. */
  83 static void add_inbuf(void)
  84 {
  85         struct scatterlist sg[1];
  86         sg_init_one(sg, inbuf, PAGE_SIZE);
  87
  88         /* We should always be able to add one buffer to an empty queue. */
  89         if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) < 0)
  90                 BUG();
  91         in_vq->vq_ops->kick(in_vq);
  92 }
  93
  94 /*D:350 get_chars() is the callback from the hvc_console infrastructure when
  95  * an interrupt is received.
  96  *
  97  * Most of the code deals with the fact that the hvc_console() infrastructure
  98  * only asks us for 16 bytes at a time.  We keep in_offset and in_used fields
  99  * for partially-filled buffers. */
 100 static int get_chars(u32 vtermno, char *buf, int count)
 101 {
 102         /* If we don't have an input queue yet, we can't get input. */
 103         BUG_ON(!in_vq);
 104
 105         /* No buffer?  Try to get one. */
 106         if (!in_len) {
 107                 in = in_vq->vq_ops->get_buf(in_vq, &in_len);
 108                 if (!in)
 109                         return 0;
 110         }
 111
 112         /* You want more than we have to give?  Well, try wanting less! */
 113         if (in_len < count)
 114                 count = in_len;
 115
 116         /* Copy across to their buffer and increment offset. */
 117         memcpy(buf, in, count);
 118         in += count;
 119         in_len -= count;
 120
 121         /* Finished?  Re-register buffer so Host will use it again. */
 122         if (in_len == 0)
 123                 add_inbuf();
 124
 125         return count;
 126 }
 127 /*:*/
 128
 129 /*D:320 Console drivers are initialized very early so boot messages can go out,
 130  * so we do things slightly differently from the generic virtio initialization
 131  * of the net and block drivers.
 132  *
 133  * At this stage, the console is output-only.  It's too early to set up a
 134  * virtqueue, so we let the drivers do some boutique early-output thing. */
 135 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
 136 {
 137         virtio_cons.put_chars = put_chars;
 138         return hvc_instantiate(0, 0, &virtio_cons);
 139 }
 140
 141 /*
 142  * virtio console configuration. This supports:
 143  * - console resize
 144  */
 145 static void virtcons_apply_config(struct virtio_device *dev)
 146 {
 147         struct winsize ws;
 148
 149         if (virtio_has_feature(dev, VIRTIO_CONSOLE_F_SIZE)) {
 150                 dev->config->get(dev,
 151                                  offsetof(struct virtio_console_config, cols),
 152                                  &ws.ws_col, sizeof(u16));
 153                 dev->config->get(dev,
 154                                  offsetof(struct virtio_console_config, rows),
 155                                  &ws.ws_row, sizeof(u16));
 156                 hvc_resize(hvc, ws);
 157         }
 158 }
 159
 160 /*
 161  * we support only one console, the hvc struct is a global var
 162  * We set the configuration at this point, since we now have a tty
 163  */
 164 static int notifier_add_vio(struct hvc_struct *hp, int data)
 165 {
 166         hp->irq_requested = 1;
 167         virtcons_apply_config(vdev);
 168
 169         return 0;
 170 }
 171
 172 static void notifier_del_vio(struct hvc_struct *hp, int data)
 173 {
 174         hp->irq_requested = 0;
 175 }
 176
 177 static void hvc_handle_input(struct virtqueue *vq)
 178 {
 179         if (hvc_poll(hvc))
 180                 hvc_kick();
 181 }
 182
 183 /*D:370 Once we're further in boot, we get probed like any other virtio device.
 184  * At this stage we set up the output virtqueue.
 185  *
 186  * To set up and manage our virtual console, we call hvc_alloc().  Since we
 187  * never remove the console device we never need this pointer again.
 188  *
 189  * Finally we put our input buffer in the input queue, ready to receive. */
 190 static int __devinit virtcons_probe(struct virtio_device *dev)
 191 {
 192         vq_callback_t *callbacks[] = { hvc_handle_input, NULL};
 193         const char *names[] = { "input", "output" };
 194         struct virtqueue *vqs[2];
 195         int err;
 196
 197         vdev = dev;
 198
 199         /* This is the scratch page we use to receive console input */
 200         inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 201         if (!inbuf) {
 202                 err = -ENOMEM;
 203                 goto fail;
 204         }
 205
 206         /* Find the queues. */
 207         /* FIXME: This is why we want to wean off hvc: we do nothing
 208          * when input comes in. */
 209         err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
 210         if (err)
 211                 goto free;
 212
 213         in_vq = vqs[0];
 214         out_vq = vqs[1];
 215
 216         /* Start using the new console output. */
 217         virtio_cons.get_chars = get_chars;
 218         virtio_cons.put_chars = put_chars;
 219         virtio_cons.notifier_add = notifier_add_vio;
 220         virtio_cons.notifier_del = notifier_del_vio;
 221         virtio_cons.notifier_hangup = notifier_del_vio;
 222
 223         /* The first argument of hvc_alloc() is the virtual console number, so
 224          * we use zero.  The second argument is the parameter for the
 225          * notification mechanism (like irq number). We currently leave this
 226          * as zero, virtqueues have implicit notifications.
 227          *
 228          * The third argument is a "struct hv_ops" containing the put_chars()
 229          * get_chars(), notifier_add() and notifier_del() pointers.
 230          * The final argument is the output buffer size: we can do any size,
 231          * so we put PAGE_SIZE here. */
 232         hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);
 233         if (IS_ERR(hvc)) {
 234                 err = PTR_ERR(hvc);
 235                 goto free_vqs;
 236         }
 237
 238         /* Register the input buffer the first time. */
 239         add_inbuf();
 240         return 0;
 241
 242 free_vqs:
 243         vdev->config->del_vqs(vdev);
 244 free:
 245         kfree(inbuf);
 246 fail:
 247         return err;
 248 }
 249
 250 static struct virtio_device_id id_table[] = {
 251         { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
 252         { 0 },
 253 };
 254
 255 static unsigned int features[] = {
 256         VIRTIO_CONSOLE_F_SIZE,
 257 };
 258
 259 static struct virtio_driver virtio_console = {
 260         .feature_table = features,
 261         .feature_table_size = ARRAY_SIZE(features),
 262         .driver.name =  KBUILD_MODNAME,
 263         .driver.owner = THIS_MODULE,
 264         .id_table =     id_table,
 265         .probe =        virtcons_probe,
 266         .config_changed = virtcons_apply_config,
 267 };
 268
 269 static int __init init(void)
 270 {
 271         return register_virtio_driver(&virtio_console);
 272 }
 273 module_init(init);
 274
 275 MODULE_DEVICE_TABLE(virtio, id_table);
 276 MODULE_DESCRIPTION("Virtio console driver");
 277 MODULE_LICENSE("GPL");