drivers/char/virtio_console.c - kernel/msm - Gitiles

 /*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 __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, 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");
	/*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 __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, 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");