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_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. */
  39 static struct virtqueue *in_vq, *out_vq;
  40 static struct virtio_device *vdev;
  41
  42 /* This is our input buffer, and how much data is left in it. */
  43 static unsigned int in_len;
  44 static char *in, *inbuf;
  45
  46 /* The operations for our console. */
  47 static 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). */
  55 static 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. */
  79 static 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. */
  96 static 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. */
 131 int __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. */
 144 static int __devinit 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
 195 free_out_vq:
 196         vdev->config->del_vq(out_vq);
 197 free_in_vq:
 198         vdev->config->del_vq(in_vq);
 199 free:
 200         kfree(inbuf);
 201 fail:
 202         return err;
 203 }
 204
 205 static struct virtio_device_id id_table[] = {
 206         { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
 207         { 0 },
 208 };
 209
 210 static 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
 217 static int __init init(void)
 218 {
 219         return register_virtio_driver(&virtio_console);
 220 }
 221 module_init(init);
 222
 223 MODULE_DEVICE_TABLE(virtio, id_table);
 224 MODULE_DESCRIPTION("Virtio console driver");
 225 MODULE_LICENSE("GPL");