[PATCH 5/6] virtio console driver

Rusty Russell
2007-09-20T12:19:21Z

This is an hvc-based virtio console driver. It's suboptimal becuase
hvc expects to have raw access to interrupts and virtio doesn't assume
that, so it currently polls.

There are two solutions: expose hvc's "kick" interface, or wean off hvc.

Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
---
drivers/char/Kconfig | 4
drivers/char/Makefile | 1
drivers/char/virtio_console.c | 232 ++++++++++++++++++++++++++++++++++++++++
include/linux/virtio_console.h | 12 ++
4 files changed, 249 insertions(+)

===================================================================
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -613,6 +613,10 @@ config HVC_XEN
help
Xen virtual console device driver

+config VIRTIO_CONSOLE
+ bool
+ select HVC_DRIVER
+
config HVCS
tristate "IBM Hypervisor Virtual Console Server support"
depends on PPC_PSERIES
===================================================================
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_HVC_BEAT) += hvc_beat.o
obj-$(CONFIG_HVC_BEAT) += hvc_beat.o
obj-$(CONFIG_HVC_DRIVER) += hvc_console.o
obj-$(CONFIG_HVC_XEN) += hvc_xen.o
+obj-$(CONFIG_VIRTIO_CONSOLE) += virtio_console.o
obj-$(CONFIG_RAW_DRIVER) += raw.o
obj-$(CONFIG_SGI_SNSC) += snsc.o snsc_event.o
obj-$(CONFIG_MSPEC) += mspec.o
===================================================================
--- /dev/null
+++ b/drivers/char/virtio_console.c
@@ -0,0 +1,232 @@
+/*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 virtqueue_ops *vq_ops;
+
+/* 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 (vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
+ /* Tell Host to go! */
+ vq_ops->kick(out_vq);
+ /* Chill out until it's done with the buffer. */
+ while (!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 (vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)
+ BUG();
+ 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 = 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);
+}
+
+/* FIXME: This is why we want to wean off hvc: we do nothing when input comes
+ * in. */
+static bool do_nothing(void *data)
+{
+ return true;
+}
+
+/*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 void *virtcons_probe(struct device *device,
+ struct virtio_config_space *config,
+ struct virtqueue_ops *new_vq_ops)
+{
+ int err;
+ struct hvc_struct *hvc;
+
+ /* This is the scratch page we use to receive console input */
+ inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!inbuf) {
+ err = -ENOMEM;
+ goto fail;
+ }
+
+ vq_ops = new_vq_ops;
+
+ /* Find the input queue. */
+ in_vq = virtio_config_vq(config, vq_ops, device, do_nothing, NULL);
+ if (IS_ERR(in_vq)) {
+ err = PTR_ERR(in_vq);
+ goto free_out_vq;
+ }
+
+ out_vq = virtio_config_vq(config, vq_ops, device, do_nothing, NULL);
+ if (IS_ERR(out_vq)) {
+ err = PTR_ERR(out_vq);
+ goto free;
+ }
+
+ /* 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_in_vq;
+ }
+
+ /* Register the input buffer the first time. */
+ add_inbuf();
+ return NULL;
+
+free_in_vq:
+ new_vq_ops->free_vq(in_vq);
+free_out_vq:
+ new_vq_ops->free_vq(out_vq);
+free:
+ kfree(inbuf);
+fail:
+ return ERR_PTR(err);
+}
+
+static struct pci_device_id id_table[] = {
+ VIRTIO_DEV_ID(VIRTIO_ID_CONSOLE, PCI_CLASS_COMMUNICATION_SERIAL),
+ { 0 },
+};
+
+static struct virtio_driver virtio_console = {
+ .name = KBUILD_MODNAME,
+ .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(pci, id_table);
+MODULE_DESCRIPTION("Virtio console driver");
+MODULE_LICENSE("GPL");
===================================================================
--- /dev/null
+++ b/include/linux/virtio_console.h
@@ -0,0 +1,12 @@
+#ifndef _LINUX_VIRTIO_CONSOLE_H
+#define _LINUX_VIRTIO_CONSOLE_H
+#include <linux/virtio_config.h>
+
+/* The ID for virtio console */
+#define VIRTIO_ID_CONSOLE 3
+
+#ifdef __KERNEL__
+int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int));
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_VIRTIO_CONSOLE_H */