diff options
Diffstat (limited to 'drivers/char/virtio_console.c')
| -rw-r--r-- | drivers/char/virtio_console.c | 225 |
1 files changed, 225 insertions, 0 deletions
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c new file mode 100644 index 00000000000..100e8a201e3 --- /dev/null +++ b/drivers/char/virtio_console.c @@ -0,0 +1,225 @@ +/*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 + * + * 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 + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * 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! */ + out_vq->vq_ops->kick(out_vq); + /* Chill out until it's done with the buffer. */ + while (!out_vq->vq_ops->get_buf(out_vq, &len)) + cpu_relax(); + } + + /* 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) + BUG(); + in_vq->vq_ops->kick(in_vq); +} + +/*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. */ + BUG_ON(!in_vq); + + /* 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) + add_inbuf(); + + 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 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, NULL); + if (IS_ERR(in_vq)) { + err = PTR_ERR(in_vq); + goto free; + } + + out_vq = vdev->config->find_vq(vdev, 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. */ + add_inbuf(); + return 0; + +free_out_vq: + vdev->config->del_vq(out_vq); +free_in_vq: + vdev->config->del_vq(in_vq); +free: + kfree(inbuf); +fail: + return err; +} + +static struct virtio_device_id id_table[] = { + { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID }, + { 0 }, +}; + +static struct virtio_driver virtio_console = { + .driver.name = 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_init(init); + +MODULE_DEVICE_TABLE(virtio, id_table); +MODULE_DESCRIPTION("Virtio console driver"); +MODULE_LICENSE("GPL"); |