Lguest support for Virtio

This makes lguest able to use the virtio devices.

We change the device descriptor page from a simple array to a variable
length "type, config_len, status, config data..." format, and
implement virtio_config_ops to read from that config data.

We use the virtio ring implementation for an efficient Guest <-> Host
virtqueue mechanism, and the new LHCALL_NOTIFY hypercall to kick the
host when it changes.

We also use LHCALL_NOTIFY on kernel addresses for very very early
console output.  We could have another hypercall, but this hack works
quite well.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/x86/lguest/Kconfig

@@ -2,8 +2,13 @@ config LGUEST_GUEST
 	bool "Lguest guest support"
 	select PARAVIRT
 	depends on !X86_PAE
+	select VIRTIO
 	select VIRTIO_RING
+	select VIRTIO_CONSOLE
 	help
 	  Lguest is a tiny in-kernel hypervisor.  Selecting this will
 	  allow your kernel to boot under lguest.  This option will increase
 	  your kernel size by about 6k.  If in doubt, say N.
+
+	  If you say Y here, make sure you say Y (or M) to the virtio block
+	  and net drivers which lguest needs.

arch/x86/lguest/boot.c

@@ -55,6 +55,7 @@
 #include <linux/clockchips.h>
 #include <linux/lguest.h>
 #include <linux/lguest_launcher.h>
+#include <linux/virtio_console.h>
 #include <asm/paravirt.h>
 #include <asm/param.h>
 #include <asm/page.h>
@@ -849,6 +850,23 @@ static __init char *lguest_memory_setup(void)
 	return "LGUEST";
 }
 
+/* Before virtqueues are set up, we use LHCALL_NOTIFY on normal memory to
+ * produce console output. */
+static __init int early_put_chars(u32 vtermno, const char *buf, int count)
+{
+	char scratch[17];
+	unsigned int len = count;
+
+	if (len > sizeof(scratch) - 1)
+		len = sizeof(scratch) - 1;
+	scratch[len] = '\0';
+	memcpy(scratch, buf, len);
+	hcall(LHCALL_NOTIFY, __pa(scratch), 0, 0);
+
+	/* This routine returns the number of bytes actually written. */
+	return len;
+}
+
 /*G:050
  * Patching (Powerfully Placating Performance Pedants)
  *
@@ -1048,6 +1066,9 @@ __init void lguest_init(void *boot)
 	 * adapted for lguest's use. */
 	add_preferred_console("hvc", 0, NULL);
 
+	/* Register our very early console. */
+	virtio_cons_early_init(early_put_chars);
+
 	/* Last of all, we set the power management poweroff hook to point to
 	 * the Guest routine to power off. */
 	pm_power_off = lguest_power_off;

drivers/lguest/Makefile

+# Guest requires the device configuration and probing code.
+obj-$(CONFIG_LGUEST_GUEST) += lguest_device.o
+
 # Host requires the other files, which can be a module.
 obj-$(CONFIG_LGUEST)	+= lg.o
 lg-y = core.o hypercalls.o page_tables.o interrupts_and_traps.o \

include/linux/lguest_launcher.h

@@ -22,37 +22,28 @@
  * complex burden for the Host and suboptimal for the Guest, so we have our own
  * "lguest" bus and simple drivers.
  *
- * Devices are described by an array of LGUEST_MAX_DEVICES of these structs,
- * placed by the Launcher just above the top of physical memory:
+ * Devices are described by a simplified ID, a status byte, and some "config"
+ * bytes which describe this device's configuration.  This is placed by the
+ * Launcher just above the top of physical memory:
  */
 struct lguest_device_desc {
-	/* The device type: console, network, disk etc. */
-	__u16 type;
-#define LGUEST_DEVICE_T_CONSOLE	1
-#define LGUEST_DEVICE_T_NET	2
-#define LGUEST_DEVICE_T_BLOCK	3
-
-	/* The specific features of this device: these depends on device type
-	 * except for LGUEST_DEVICE_F_RANDOMNESS. */
-	__u16 features;
-#define LGUEST_NET_F_NOCSUM		0x4000 /* Don't bother checksumming */
-#define LGUEST_DEVICE_F_RANDOMNESS	0x8000 /* IRQ is fairly random */
-
-	/* This is how the Guest reports status of the device: the Host can set
-	 * LGUEST_DEVICE_S_REMOVED to indicate removal, but the rest are only
-	 * ever manipulated by the Guest, and only ever set. */
-	__u16 status;
-/* 256 and above are device specific. */
-#define LGUEST_DEVICE_S_ACKNOWLEDGE	1 /* We have seen device. */
-#define LGUEST_DEVICE_S_DRIVER		2 /* We have found a driver */
-#define LGUEST_DEVICE_S_DRIVER_OK	4 /* Driver says OK! */
-#define LGUEST_DEVICE_S_REMOVED		8 /* Device has gone away. */
-#define LGUEST_DEVICE_S_REMOVED_ACK	16 /* Driver has been told. */
-#define LGUEST_DEVICE_S_FAILED		128 /* Something actually failed */
+	/* The device type: console, network, disk etc.  Type 0 terminates. */
+	__u8 type;
+	/* The number of bytes of the config array. */
+	__u8 config_len;
+	/* A status byte, written by the Guest. */
+	__u8 status;
+	__u8 config[0];
+};
 
-	/* Each device exists somewhere in Guest physical memory, over some
-	 * number of pages. */
-	__u16 num_pages;
+/*D:135 This is how we expect the device configuration field for a virtqueue
+ * (type VIRTIO_CONFIG_F_VIRTQUEUE) to be laid out: */
+struct lguest_vqconfig {
+	/* The number of entries in the virtio_ring */
+	__u16 num;
+	/* The interrupt we get when something happens. */
+	__u16 irq;
+	/* The page number of the virtio ring for this device. */
 	__u32 pfn;
 };
 /*:*/