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[Xen-devel] [patch 17/21] Xen-paravirt: Add the Xen virtual console driver.



This provides a bootstrap and ongoing emergency console which is
intended to be available from very early during boot and at all times
thereafter, in contrast with alternatives such as UDP-based syslogd,
or logging in via ssh. The protocol is based on a simple shared-memory
ring buffer.

Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Cc: Alan <alan@xxxxxxxxxxxxxxxxxxx>

---
 arch/i386/kernel/early_printk.c    |    2 
 drivers/Makefile                   |    3 
 drivers/xen/Makefile               |    1 
 drivers/xen/console/Makefile       |    2 
 drivers/xen/console/console.c      |  585 +++++++++++++++++++++++++++++++++++
 drivers/xen/console/xencons_ring.c |  144 ++++++++
 include/xen/xencons.h              |   14 
 init/main.c                        |    2 
 8 files changed, 753 insertions(+)

===================================================================
--- a/arch/i386/kernel/early_printk.c
+++ b/arch/i386/kernel/early_printk.c
@@ -1,2 +1,4 @@
 
+#ifndef CONFIG_XEN
 #include "../../x86_64/kernel/early_printk.c"
+#endif
===================================================================
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -14,6 +14,9 @@ obj-$(CONFIG_ACPI)            += acpi/
 # was used and do nothing if so
 obj-$(CONFIG_PNP)              += pnp/
 obj-$(CONFIG_ARM_AMBA)         += amba/
+
+# Xen is the default console when running as a guest
+obj-$(CONFIG_XEN)              += xen/
 
 # char/ comes before serial/ etc so that the VT console is the boot-time
 # default.
===================================================================
--- /dev/null
+++ b/drivers/xen/Makefile
@@ -0,0 +1,1 @@
+obj-y  += console/
===================================================================
--- /dev/null
+++ b/drivers/xen/console/Makefile
@@ -0,0 +1,2 @@
+
+obj-y  := console.o xencons_ring.o
===================================================================
--- /dev/null
+++ b/drivers/xen/console/console.c
@@ -0,0 +1,585 @@
+/******************************************************************************
+ * console.c
+ * 
+ * Virtual console driver.
+ * 
+ * Copyright (c) 2002-2004, K A Fraser.
+ * 
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial.h>
+#include <linux/major.h>
+#include <linux/ptrace.h>
+#include <linux/ioport.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/bootmem.h>
+#include <linux/sysrq.h>
+#include <linux/vt.h>
+
+#include <asm/io.h>
+#include <asm/irq.h>
+#include <asm/uaccess.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/event_channel.h>
+#include <asm/xen/hypervisor.h>
+#include <xen/events.h>
+#include <xen/xencons.h>
+
+MODULE_LICENSE("Dual BSD/GPL");
+
+static int xc_disabled = 0;
+static int xc_num = -1;
+
+/* /dev/xvc0 device number allocated by lanana.org. */
+#define XEN_XVC_MAJOR 204
+#define XEN_XVC_MINOR 191
+
+#ifdef CONFIG_MAGIC_SYSRQ
+static unsigned long sysrq_requested;
+#endif
+
+static int __init xencons_setup(char *str)
+{
+       if (!strcmp(str, "off"))
+               xc_disabled = 1;
+       return 1;
+}
+__setup("xencons=", xencons_setup);
+
+/* The kernel and user-land drivers share a common transmit buffer. */
+static unsigned int wbuf_size = 4096;
+#define WBUF_MASK(_i) ((_i)&(wbuf_size-1))
+static char *wbuf;
+static unsigned int wc, wp; /* write_cons, write_prod */
+
+static int __init xencons_bufsz_setup(char *str)
+{
+       unsigned int goal;
+       goal = simple_strtoul(str, NULL, 0);
+       if (goal) {
+               goal = roundup_pow_of_two(goal);
+               if (wbuf_size < goal)
+                       wbuf_size = goal;
+       }
+       return 1;
+}
+__setup("xencons_bufsz=", xencons_bufsz_setup);
+
+/* This lock protects accesses to the common transmit buffer. */
+static DEFINE_SPINLOCK(xencons_lock);
+
+/* Common transmit-kick routine. */
+static void __xencons_tx_flush(void);
+
+static struct tty_driver *xencons_driver;
+
+/******************** Kernel console driver ********************************/
+
+static void kcons_write(struct console *c, const char *s, unsigned int count)
+{
+       int           i = 0;
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+
+       while (i < count) {
+               for (; i < count; i++) {
+                       if ((wp - wc) >= (wbuf_size - 1))
+                               break;
+                       if ((wbuf[WBUF_MASK(wp++)] = s[i]) == '\n')
+                               wbuf[WBUF_MASK(wp++)] = '\r';
+               }
+
+               __xencons_tx_flush();
+       }
+
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static void kcons_write_dom0(struct console *c, const char *s, unsigned int 
count)
+{
+       while (count > 0) {
+               int rc;
+               rc = HYPERVISOR_console_io(CONSOLEIO_write, count, (char *)s);
+               if (rc <= 0)
+                       break;
+               count -= rc;
+               s += rc;
+       }
+}
+
+void early_printk(const char *fmt, ...)
+{
+       va_list args;
+       int printk_len;
+       static char printk_buf[1024];
+
+       /* Emit the output into the temporary buffer */
+       va_start(args, fmt);
+       printk_len = vsnprintf(printk_buf, sizeof(printk_buf), fmt, args);
+       va_end(args);
+
+       /* Send the processed output directly to Xen. */
+       kcons_write_dom0(NULL, printk_buf, printk_len);
+}
+
+static struct console early_xen_console = {
+       .name =         "earlyxen",
+       .write =        kcons_write_dom0,
+       .flags =        CON_PRINTBUFFER,
+       .index =        -1,
+};
+
+static int early_console_initialized = 0;
+
+int __init setup_early_printk(char *opt)
+{
+       early_console_initialized = 1;
+       register_console(&early_xen_console);
+
+       return 0;
+}
+
+void __init disable_early_printk(void)
+{
+       if (!early_console_initialized)
+               return;
+       printk("disabling early console\n");
+       unregister_console(&early_xen_console);
+       early_console_initialized = 0;
+}
+
+static struct tty_driver *kcons_device(struct console *c, int *index)
+{
+       *index = 0;
+       return xencons_driver;
+}
+
+static struct console kcons_info = {
+       .name   = "xvc",
+       .device = kcons_device,
+       .flags  = CON_PRINTBUFFER | CON_ENABLED,
+       .index  = -1,
+};
+
+static int __init xen_console_init(void)
+{
+       if (!is_running_on_xen())
+               goto out;
+       if (xc_disabled)
+               goto out;
+
+       if (is_initial_xendomain()) {
+               kcons_info.write = kcons_write_dom0;
+       } else {
+               if (!xen_start_info->console.domU.evtchn)
+                       goto out;
+               kcons_info.write = kcons_write;
+       }
+       if (xc_num == -1)
+               xc_num = 0;
+
+       wbuf = alloc_bootmem(wbuf_size);
+
+       register_console(&kcons_info);
+
+out:
+       return 0;
+}
+console_initcall(xen_console_init);
+
+/*** Forcibly flush console data before dying. ***/
+void xencons_force_flush(void)
+{
+       int sz;
+
+       /* Emergency console is synchronous, so there's nothing to flush. */
+       if (!is_running_on_xen() ||
+           is_initial_xendomain() ||
+           !xen_start_info->console.domU.evtchn)
+               return;
+
+       /* Spin until console data is flushed through to the daemon. */
+       while (wc != wp) {
+               int sent = 0;
+               if ((sz = wp - wc) == 0)
+                       continue;
+               sent = xencons_ring_send(&wbuf[WBUF_MASK(wc)], sz);
+               if (sent > 0)
+                       wc += sent;
+       }
+}
+
+
+/******************** User-space console driver (/dev/console) ************/
+
+#define DRV(_d)         (_d)
+
+static struct ktermios *xencons_termios[1];
+static struct ktermios *xencons_termios_locked[1];
+static struct tty_struct *xencons_tty;
+static int xencons_priv_irq;
+static char x_char;
+
+void xencons_rx(char *buf, unsigned len)
+{
+       int           i;
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       if (xencons_tty == NULL)
+               goto out;
+
+       for (i = 0; i < len; i++) {
+#ifdef CONFIG_MAGIC_SYSRQ
+               if (sysrq_on()) {
+                       if (buf[i] == '\x0f') { /* ^O */
+                               sysrq_requested = jiffies;
+                               continue; /* don't print the sysrq key */
+                       } else if (sysrq_requested) {
+                               unsigned long sysrq_timeout =
+                                       sysrq_requested + HZ*2;
+                               sysrq_requested = 0;
+                               if (time_before(jiffies, sysrq_timeout)) {
+                                       spin_unlock_irqrestore(
+                                               &xencons_lock, flags);
+                                       handle_sysrq(
+                                               buf[i], xencons_tty);
+                                       spin_lock_irqsave(
+                                               &xencons_lock, flags);
+                                       continue;
+                               }
+                       }
+               }
+#endif
+               tty_insert_flip_char(xencons_tty, buf[i], TTY_NORMAL);
+       }
+       tty_flip_buffer_push(xencons_tty);
+
+ out:
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static void __xencons_tx_flush(void)
+{
+       int sent, sz, work_done = 0;
+
+       if (x_char) {
+               if (is_initial_xendomain())
+                       kcons_write_dom0(NULL, &x_char, 1);
+               else
+                       while (x_char)
+                               if (xencons_ring_send(&x_char, 1) == 1)
+                                       break;
+               x_char = 0;
+               work_done = 1;
+       }
+
+       while (wc != wp) {
+               sz = wp - wc;
+               if (sz > (wbuf_size - WBUF_MASK(wc)))
+                       sz = wbuf_size - WBUF_MASK(wc);
+               if (is_initial_xendomain()) {
+                       kcons_write_dom0(NULL, &wbuf[WBUF_MASK(wc)], sz);
+                       wc += sz;
+               } else {
+                       sent = xencons_ring_send(&wbuf[WBUF_MASK(wc)], sz);
+                       if (sent == 0)
+                               break;
+                       wc += sent;
+               }
+               work_done = 1;
+       }
+
+       if (work_done && (xencons_tty != NULL)) {
+               wake_up_interruptible(&xencons_tty->write_wait);
+               tty_wakeup(xencons_tty);
+       }
+}
+
+void xencons_tx(void)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       __xencons_tx_flush();
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+/* Privileged receive callback and transmit kicker. */
+static irqreturn_t xencons_priv_interrupt(int irq, void *dev_id)
+{
+       static char rbuf[16];
+       int         l;
+
+       while ((l = HYPERVISOR_console_io(CONSOLEIO_read, 16, rbuf)) > 0)
+               xencons_rx(rbuf, l);
+
+       xencons_tx();
+
+       return IRQ_HANDLED;
+}
+
+static int xencons_write_room(struct tty_struct *tty)
+{
+       return wbuf_size - (wp - wc);
+}
+
+static int xencons_chars_in_buffer(struct tty_struct *tty)
+{
+       return wp - wc;
+}
+
+static void xencons_send_xchar(struct tty_struct *tty, char ch)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       x_char = ch;
+       __xencons_tx_flush();
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static void xencons_throttle(struct tty_struct *tty)
+{
+       if (I_IXOFF(tty))
+               xencons_send_xchar(tty, STOP_CHAR(tty));
+}
+
+static void xencons_unthrottle(struct tty_struct *tty)
+{
+       if (I_IXOFF(tty)) {
+               if (x_char != 0)
+                       x_char = 0;
+               else
+                       xencons_send_xchar(tty, START_CHAR(tty));
+       }
+}
+
+static void xencons_flush_buffer(struct tty_struct *tty)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       wc = wp = 0;
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static inline int __xencons_put_char(unsigned char ch)
+{
+       if ((wp - wc) == wbuf_size)
+               return 0;
+       wbuf[WBUF_MASK(wp++)] = ch;
+       return 1;
+}
+
+static int xencons_write(
+       struct tty_struct *tty,
+       const unsigned char *buf,
+       int count)
+{
+       int i;
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+
+       for (i = 0; i < count; i++)
+               if (!__xencons_put_char(buf[i]))
+                       break;
+
+       if (i != 0)
+               __xencons_tx_flush();
+
+       spin_unlock_irqrestore(&xencons_lock, flags);
+
+       return i;
+}
+
+static void xencons_put_char(struct tty_struct *tty, unsigned char ch)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       (void)__xencons_put_char(ch);
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static void xencons_flush_chars(struct tty_struct *tty)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       __xencons_tx_flush();
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static void xencons_wait_until_sent(struct tty_struct *tty, int timeout)
+{
+       unsigned long orig_jiffies = jiffies;
+
+       while (DRV(tty->driver)->chars_in_buffer(tty)) {
+               set_current_state(TASK_INTERRUPTIBLE);
+               schedule_timeout(1);
+               if (signal_pending(current))
+                       break;
+               if (timeout && time_after(jiffies, orig_jiffies + timeout))
+                       break;
+       }
+
+       set_current_state(TASK_RUNNING);
+}
+
+static int xencons_open(struct tty_struct *tty, struct file *filp)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&xencons_lock, flags);
+       tty->driver_data = NULL;
+       if (xencons_tty == NULL)
+               xencons_tty = tty;
+       __xencons_tx_flush();
+       spin_unlock_irqrestore(&xencons_lock, flags);
+
+       return 0;
+}
+
+static void xencons_close(struct tty_struct *tty, struct file *filp)
+{
+       unsigned long flags;
+
+       mutex_lock(&tty_mutex);
+
+       if (tty->count != 1) {
+               mutex_unlock(&tty_mutex);
+               return;
+       }
+
+       /* Prevent other threads from re-opening this tty. */
+       set_bit(TTY_CLOSING, &tty->flags);
+       mutex_unlock(&tty_mutex);
+
+       tty->closing = 1;
+       tty_wait_until_sent(tty, 0);
+       if (DRV(tty->driver)->flush_buffer != NULL)
+               DRV(tty->driver)->flush_buffer(tty);
+       if (tty->ldisc.flush_buffer != NULL)
+               tty->ldisc.flush_buffer(tty);
+       tty->closing = 0;
+       spin_lock_irqsave(&xencons_lock, flags);
+       xencons_tty = NULL;
+       spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static struct tty_operations xencons_ops = {
+       .open = xencons_open,
+       .close = xencons_close,
+       .write = xencons_write,
+       .write_room = xencons_write_room,
+       .put_char = xencons_put_char,
+       .flush_chars = xencons_flush_chars,
+       .chars_in_buffer = xencons_chars_in_buffer,
+       .send_xchar = xencons_send_xchar,
+       .flush_buffer = xencons_flush_buffer,
+       .throttle = xencons_throttle,
+       .unthrottle = xencons_unthrottle,
+       .wait_until_sent = xencons_wait_until_sent,
+};
+
+static int __init xencons_init(void)
+{
+       int rc;
+
+       if (!is_running_on_xen())
+               return -ENODEV;
+
+       if (xc_disabled)
+               return 0;
+
+       if (!is_initial_xendomain()) {
+               rc = xencons_ring_init();
+               if (rc)
+                       return rc;
+       }
+
+       xencons_driver = alloc_tty_driver(1);
+       if (xencons_driver == NULL)
+               return -ENOMEM;
+
+       DRV(xencons_driver)->name            = "xvc";
+       DRV(xencons_driver)->major           = XEN_XVC_MAJOR;
+       DRV(xencons_driver)->minor_start     = XEN_XVC_MINOR;
+       DRV(xencons_driver)->name_base       = xc_num;
+       DRV(xencons_driver)->type            = TTY_DRIVER_TYPE_SERIAL;
+       DRV(xencons_driver)->subtype         = SERIAL_TYPE_NORMAL;
+       DRV(xencons_driver)->init_termios    = tty_std_termios;
+       DRV(xencons_driver)->flags           =
+               TTY_DRIVER_REAL_RAW |
+               TTY_DRIVER_RESET_TERMIOS |
+               TTY_DRIVER_DYNAMIC_DEV;
+       DRV(xencons_driver)->termios         = xencons_termios;
+       DRV(xencons_driver)->termios_locked  = xencons_termios_locked;
+
+       tty_set_operations(xencons_driver, &xencons_ops);
+
+       if ((rc = tty_register_driver(DRV(xencons_driver))) != 0) {
+               printk("WARNING: Failed to register Xen virtual "
+                      "console driver as '%s%d'\n",
+                      DRV(xencons_driver)->name,
+                      DRV(xencons_driver)->name_base);
+               put_tty_driver(xencons_driver);
+               xencons_driver = NULL;
+               return rc;
+       }
+
+       if (is_initial_xendomain()) {
+               xencons_priv_irq = bind_virq_to_irqhandler(
+                       VIRQ_CONSOLE,
+                       0,
+                       xencons_priv_interrupt,
+                       0,
+                       "console",
+                       NULL);
+               BUG_ON(xencons_priv_irq < 0);
+       }
+
+       printk("Xen virtual console successfully installed as %s%d\n",
+              DRV(xencons_driver)->name, xc_num);
+
+       return 0;
+}
+
+module_init(xencons_init);
===================================================================
--- /dev/null
+++ b/drivers/xen/console/xencons_ring.c
@@ -0,0 +1,144 @@
+/* 
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial.h>
+#include <linux/major.h>
+#include <linux/ptrace.h>
+#include <linux/ioport.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+#include <asm/xen/hypervisor.h>
+#include <linux/wait.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/err.h>
+#include <xen/interface/io/console.h>
+#include <xen/events.h>
+#include <xen/xencons.h>
+#include <xen/page.h>
+
+static int xencons_irq;
+
+static inline struct xencons_interface *xencons_interface(void)
+{
+       return mfn_to_virt(xen_start_info->console.domU.mfn);
+}
+
+static inline void notify_daemon(void)
+{
+       /* Use evtchn: this is called early, before irq is set up. */
+       notify_remote_via_evtchn(xen_start_info->console.domU.evtchn);
+}
+
+int xencons_ring_send(const char *data, unsigned len)
+{
+       int sent = 0;
+       struct xencons_interface *intf = xencons_interface();
+       XENCONS_RING_IDX cons, prod;
+
+       cons = intf->out_cons;
+       prod = intf->out_prod;
+       mb();
+       BUG_ON((prod - cons) > sizeof(intf->out));
+
+       while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
+               intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
+
+       wmb();
+       intf->out_prod = prod;
+
+       notify_daemon();
+
+       return sent;
+}
+
+static irqreturn_t handle_input(int irq, void *unused)
+{
+       struct xencons_interface *intf = xencons_interface();
+       XENCONS_RING_IDX cons, prod;
+
+       cons = intf->in_cons;
+       prod = intf->in_prod;
+       mb();
+       BUG_ON((prod - cons) > sizeof(intf->in));
+
+       while (cons != prod) {
+               xencons_rx(intf->in+MASK_XENCONS_IDX(cons,intf->in), 1);
+               cons++;
+       }
+
+       mb();
+       intf->in_cons = cons;
+
+       notify_daemon();
+
+       xencons_tx();
+
+       return IRQ_HANDLED;
+}
+
+int xencons_ring_init(void)
+{
+       int irq;
+
+       if (xencons_irq)
+               unbind_from_irqhandler(xencons_irq, NULL);
+       xencons_irq = 0;
+
+       if (!is_running_on_xen() ||
+           is_initial_xendomain() ||
+           !xen_start_info->console.domU.evtchn)
+               return -ENODEV;
+
+       irq = bind_evtchn_to_irqhandler(
+               xen_start_info->console.domU.evtchn,
+               handle_input, 0, "xencons", NULL);
+       if (irq < 0) {
+               printk(KERN_ERR "XEN console request irq failed %i\n", irq);
+               return irq;
+       }
+
+       xencons_irq = irq;
+
+       /* In case we have in-flight data after save/restore... */
+       notify_daemon();
+
+       return 0;
+}
+
+void xencons_resume(void)
+{
+       (void)xencons_ring_init();
+}
===================================================================
--- /dev/null
+++ b/include/xen/xencons.h
@@ -0,0 +1,14 @@
+#ifndef __ASM_XENCONS_H__
+#define __ASM_XENCONS_H__
+
+void xencons_force_flush(void);
+void xencons_resume(void);
+
+/* Interrupt work hooks. Receive data, or kick data out. */
+void xencons_rx(char *buf, unsigned len);
+void xencons_tx(void);
+
+int xencons_ring_init(void);
+int xencons_ring_send(const char *data, unsigned len);
+
+#endif /* __ASM_XENCONS_H__ */
===================================================================
--- a/init/main.c
+++ b/init/main.c
@@ -495,6 +495,8 @@ asmlinkage void __init start_kernel(void
        unwind_init();
        lockdep_init();
 
+       //setup_early_printk(NULL);
+
        local_irq_disable();
        early_boot_irqs_off();
        early_init_irq_lock_class();

-- 


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