Re: [RFC PATCH 29/35] Add the Xen virtual console driver.
From: Anthony Liguori
Date: Wed Mar 22 2006 - 10:58:21 EST
Chris Wright wrote:
+/*
+ * Modes:
+ * 'xencons=off' [XC_OFF]: Console is disabled.
+ * 'xencons=tty' [XC_TTY]: Console attached to '/dev/tty[0-9]+'.
+ * 'xencons=ttyS' [XC_SERIAL]: Console attached to '/dev/ttyS[0-9]+'.
+ * [XC_DEFAULT]: DOM0 -> XC_SERIAL ; all others -> XC_TTY.
+ *
+ * NB. In mode XC_TTY, we create dummy consoles for tty2-63. This suppresses
+ * warnings from standard distro startup scripts.
+ */
This has always seemed a bit wrong to me and makes a number of things
kind of awkward (like a virtual video driver).
It would seem better me to treat this driver as what it really is, a
virtual serial device. It adds a little bit of additional work to the
userspace tools (they just have to make sure to pass console=ttyS0) but
it seems worth it.
We could also solve the tty[0-9] problem by implementing a proper
console driver that could use multiple virtual serial devices if we
wanted to go that route.
Another option would be to just emulate a serial driver. The console
driver isn't really performance critical. It seems to me that it's a
bit unnecessary to even bother paravirtualizing the console device when
it's so easy to emulate.
Regards,
Anthony Liguori
+static enum { XC_OFF, XC_DEFAULT, XC_TTY, XC_SERIAL } xc_mode = XC_DEFAULT;
+static int xc_num = -1;
+
+#ifdef CONFIG_MAGIC_SYSRQ
+static unsigned long sysrq_requested;
+extern int sysrq_enabled;
+#endif
+
+static int __init xencons_setup(char *str)
+{
+ char *q;
+ int n;
+
+ if (!strncmp(str, "ttyS", 4))
+ xc_mode = XC_SERIAL;
+ else if (!strncmp(str, "tty", 3))
+ xc_mode = XC_TTY;
+ else if (!strncmp(str, "off", 3))
+ xc_mode = XC_OFF;
+
+ switch (xc_mode) {
+ case XC_SERIAL:
+ n = simple_strtol(str+4, &q, 10);
+ if (q > (str + 4))
+ xc_num = n;
+ break;
+ case XC_TTY:
+ n = simple_strtol(str+3, &q, 10);
+ if (q > (str + 3))
+ xc_num = n;
+ break;
+ default:
+ break;
+ }
+
+ 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);
+ while (wbuf_size < goal)
+ wbuf_size <<= 1;
+ return 1;
+}
+__setup("xencons_bufsz=", xencons_bufsz_setup);
+
+/* This lock protects accesses to the common transmit buffer. */
+static spinlock_t xencons_lock = SPIN_LOCK_UNLOCKED;
+
+/* 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)
+{
+ int rc;
+
+ while ((count > 0) &&
+ ((rc = HYPERVISOR_console_io(
+ CONSOLEIO_write, count, (char *)s)) > 0)) {
+ count -= rc;
+ s += rc;
+ }
+}
+
+static struct tty_driver *kcons_device(struct console *c, int *index)
+{
+ *index = 0;
+ return xencons_driver;
+}
+
+static struct console kcons_info = {
+ .device = kcons_device,
+ .flags = CON_PRINTBUFFER,
+ .index = -1,
+};
+
+#define __RETCODE 0
+static int __init xen_console_init(void)
+{
+ if (xen_init() < 0)
+ return __RETCODE;
+
+ if (xen_start_info->flags & SIF_INITDOMAIN) {
+ if (xc_mode == XC_DEFAULT)
+ xc_mode = XC_SERIAL;
+ kcons_info.write = kcons_write_dom0;
+ if (xc_mode == XC_SERIAL)
+ kcons_info.flags |= CON_ENABLED;
+ } else {
+ if (xc_mode == XC_DEFAULT)
+ xc_mode = XC_TTY;
+ kcons_info.write = kcons_write;
+ }
+
+ switch (xc_mode) {
+ case XC_SERIAL:
+ strcpy(kcons_info.name, "ttyS");
+ if (xc_num == -1)
+ xc_num = 0;
+ break;
+
+ case XC_TTY:
+ strcpy(kcons_info.name, "tty");
+ if (xc_num == -1)
+ xc_num = 1;
+ break;
+
+ default:
+ return __RETCODE;
+ }
+
+ wbuf = alloc_bootmem(wbuf_size);
+
+ register_console(&kcons_info);
+
+ return __RETCODE;
+}
+console_initcall(xen_console_init);
+
+/*** Useful function for console debugging -- goes straight to Xen. ***/
+asmlinkage int xprintk(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);
+
+ return 0;
+}
+
+/*** Forcibly flush console data before dying. ***/
+void xencons_force_flush(void)
+{
+ int sz;
+
+ /* Emergency console is synchronous, so there's nothing to flush. */
+ if (xen_start_info->flags & SIF_INITDOMAIN)
+ 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)
+#define TTY_INDEX(_tty) ((_tty)->index)
+
+static struct termios *xencons_termios[MAX_NR_CONSOLES];
+static struct termios *xencons_termios_locked[MAX_NR_CONSOLES];
+static struct tty_struct *xencons_tty;
+static int xencons_priv_irq;
+static char x_char;
+
+void xencons_rx(char *buf, unsigned len, struct pt_regs *regs)
+{
+ 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_enabled) {
+ 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], regs, xencons_tty);
+ spin_lock_irqsave(
+ &xencons_lock, flags);
+ continue;
+ }
+ }
+ }
+#endif
+ tty_insert_flip_char(xencons_tty, buf[i], 0);
+ }
+ 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 (xen_start_info->flags & SIF_INITDOMAIN)
+ 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 (xen_start_info->flags & SIF_INITDOMAIN) {
+ 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);
+ if ((xencons_tty->flags & (1 << TTY_DO_WRITE_WAKEUP)) &&
+ (xencons_tty->ldisc.write_wakeup != NULL))
+ (xencons_tty->ldisc.write_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,
+ struct pt_regs *regs)
+{
+ static char rbuf[16];
+ int l;
+
+ while ((l = HYPERVISOR_console_io(CONSOLEIO_read, 16, rbuf)) > 0)
+ xencons_rx(rbuf, l, regs);
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ 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 (TTY_INDEX(tty) != 0)
+ return;
+
+ if (I_IXOFF(tty))
+ xencons_send_xchar(tty, STOP_CHAR(tty));
+}
+
+static void xencons_unthrottle(struct tty_struct *tty)
+{
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ spin_lock_irqsave(&xencons_lock, flags);
+ wc = wp = 0;
+ spin_unlock_irqrestore(&xencons_lock, flags);
+}
+
+static inline int __xencons_put_char(int ch)
+{
+ char _ch = (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;
+
+ if (TTY_INDEX(tty) != 0)
+ return count;
+
+ 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, u_char ch)
+{
+ unsigned long flags;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return 0;
+
+ 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;
+
+ if (TTY_INDEX(tty) != 0)
+ return;
+
+ if (tty->count == 1) {
+ 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 (xen_init() < 0)
+ return -ENODEV;
+
+ if (xc_mode == XC_OFF)
+ return 0;
+
+ xencons_ring_init();
+
+ xencons_driver = alloc_tty_driver((xc_mode == XC_SERIAL) ?
+ 1 : MAX_NR_CONSOLES);
+ if (xencons_driver == NULL)
+ return -ENOMEM;
+
+ DRV(xencons_driver)->name = "xencons";
+ DRV(xencons_driver)->major = TTY_MAJOR;
+ 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_NO_DEVFS;
+ DRV(xencons_driver)->termios = xencons_termios;
+ DRV(xencons_driver)->termios_locked = xencons_termios_locked;
+
+ if (xc_mode == XC_SERIAL) {
+ DRV(xencons_driver)->name = "ttyS";
+ DRV(xencons_driver)->minor_start = 64 + xc_num;
+ DRV(xencons_driver)->name_base = 0 + xc_num;
+ } else {
+ DRV(xencons_driver)->name = "tty";
+ DRV(xencons_driver)->minor_start = xc_num;
+ DRV(xencons_driver)->name_base = xc_num;
+ }
+
+ 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;
+ }
+
+ tty_register_device(xencons_driver, 0, NULL);
+
+ if (xen_start_info->flags & SIF_INITDOMAIN) {
+ 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,
+ DRV(xencons_driver)->name_base );
+
+ return 0;
+}
+
+module_init(xencons_init);
--- /dev/null
+++ xen-subarch-2.6/drivers/xen/console/xencons_ring.c
@@ -0,0 +1,115 @@
+#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/hypervisor.h>
+#include <xen/evtchn.h>
+#include <xen/xencons.h>
+#include <linux/wait.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/err.h>
+#include <xen/interface/io/console.h>
+
+static int xencons_irq;
+
+static inline struct xencons_interface *xencons_interface(void)
+{
+ return mfn_to_virt(xen_start_info->console_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_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 pt_regs *regs)
+{
+ 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, regs);
+ cons++;
+ }
+
+ mb();
+ intf->in_cons = cons;
+
+ notify_daemon();
+
+ xencons_tx();
+
+ return IRQ_HANDLED;
+}
+
+int xencons_ring_init(void)
+{
+ int err;
+
+ if (xencons_irq)
+ unbind_from_irqhandler(xencons_irq, NULL);
+ xencons_irq = 0;
+
+ if (!xen_start_info->console_evtchn)
+ return 0;
+
+ err = bind_evtchn_to_irqhandler(
+ xen_start_info->console_evtchn,
+ handle_input, 0, "xencons", NULL);
+ if (err <= 0) {
+ printk(KERN_ERR "XEN console request irq failed %i\n", err);
+ return err;
+ }
+
+ xencons_irq = err;
+
+ /* In case we have in-flight data after save/restore... */
+ notify_daemon();
+
+ return 0;
+}
+
+void xencons_resume(void)
+{
+ (void)xencons_ring_init();
+}
--- /dev/null
+++ xen-subarch-2.6/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, struct pt_regs *regs);
+void xencons_tx(void);
+
+int xencons_ring_init(void);
+int xencons_ring_send(const char *data, unsigned len);
+
+#endif /* __ASM_XENCONS_H__ */
--
------------------------------------------------------------------------
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