[Xen-devel] Xen virtual console driver question

[Amos Waterland <apw@xxxxxxxxxx>]

What is the plan for the future of the Xen virtual console driver?  Will
it continue to hijack /dev/ttyS0 or get its own device like /dev/xencons?

The reason I ask is that I need a single Linux kernel binary, including
one with builtin console=X command line arguments, to run on bare
hardware and as a dom0 under Xen.  Xen's current approach is to disable
the physical serial port drivers in the Linux .config, which I need
enabled to run properly on bare JS21 blades.

I am currently using the below patch, but would really prefer not to.
It's basic approach is to have the Xen virtual console driver react
"gracefully" in the case that a real serial driver has already
registered ttyS0-ttyS3.  It's current behavior is to fail if the 8250
driver was initialized ahead of it, and console is lost.  In the process
I found a bug in Linux, and have included the patch for it since
otherwise the Xen driver initialization will succeed but with negative
side effects in the kobject subsystem.

What is the story?

---

diff -r 17aa29a18b08 arch/powerpc/configs/xen_maple_defconfig
--- a/arch/powerpc/configs/xen_maple_defconfig  Thu Jul 27 18:57:20 2006 -0400
+++ b/arch/powerpc/configs/xen_maple_defconfig  Mon Jul 31 21:04:17 2006 -0400
@@ -704,10 +704,18 @@ CONFIG_HW_CONSOLE=y
 #
 # Serial drivers
 #
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+CONFIG_SERIAL_8250_PCI=y
+CONFIG_SERIAL_8250_NR_UARTS=4
+CONFIG_SERIAL_8250_RUNTIME_UARTS=4
+# CONFIG_SERIAL_8250_EXTENDED is not set
 
 #
 # Non-8250 serial port support
 #
+CONFIG_SERIAL_CORE=y
+CONFIG_SERIAL_CORE_CONSOLE=y
 # CONFIG_SERIAL_ICOM is not set
 # CONFIG_SERIAL_JSM is not set
 CONFIG_UNIX98_PTYS=y
@@ -1307,7 +1315,7 @@ CONFIG_XEN_BLKDEV_FRONTEND=y
 CONFIG_XEN_BLKDEV_FRONTEND=y
 CONFIG_XEN_NETDEV_FRONTEND=y
 CONFIG_XEN_SCRUB_PAGES=y
-CONFIG_XEN_DISABLE_SERIAL=y
+# CONFIG_XEN_DISABLE_SERIAL is not set
 CONFIG_XEN_SYSFS=y
 # CONFIG_XEN_COMPAT_030002_AND_LATER is not set
 CONFIG_XEN_COMPAT_LATEST_ONLY=y
diff -r 17aa29a18b08 drivers/xen/console/console.c
--- a/drivers/xen/console/console.c     Thu Jul 27 18:57:20 2006 -0400
+++ b/drivers/xen/console/console.c     Mon Jul 31 21:04:17 2006 -0400
@@ -70,6 +70,7 @@
  */
 static enum { XC_OFF, XC_DEFAULT, XC_TTY, XC_SERIAL } xc_mode = XC_DEFAULT;
 static int xc_num = -1;
+enum { XC_NUM_MAX = 8 };
 
 #ifdef CONFIG_MAGIC_SYSRQ
 static unsigned long sysrq_requested;
@@ -576,6 +577,7 @@ static int __init xencons_init(void)
 
        xencons_ring_init();
 
+retry:
        xencons_driver = alloc_tty_driver((xc_mode == XC_SERIAL) ?
                                          1 : MAX_NR_CONSOLES);
        if (xencons_driver == NULL)
@@ -612,6 +614,15 @@ static int __init xencons_init(void)
                       DRV(xencons_driver)->name_base);
                put_tty_driver(xencons_driver);
                xencons_driver = NULL;
+
+               /* Somebody, almost certainly the real serial port
+                  driver, registered ahead of us, so find the first
+                  unused minor.  */
+               if (xc_num <= XC_NUM_MAX) {
+                   xc_num++;
+                   goto retry;
+               }
+
                return rc;
        }
 
diff -r 17aa29a18b08 fs/char_dev.c
--- a/fs/char_dev.c     Thu Jul 27 18:57:20 2006 -0400
+++ b/fs/char_dev.c     Mon Jul 31 21:04:17 2006 -0400
@@ -111,10 +111,13 @@ __register_chrdev_region(unsigned int ma
 
        for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
                if ((*cp)->major > major ||
-                   ((*cp)->major == major && (*cp)->baseminor >= baseminor))
+                   ((*cp)->major == major &&
+                    (((*cp)->baseminor >= baseminor) ||
+                     ((*cp)->baseminor + (*cp)->minorct > baseminor))))
                        break;
        if (*cp && (*cp)->major == major &&
-           (*cp)->baseminor < baseminor + minorct) {
+           (((*cp)->baseminor < baseminor + minorct) ||
+            ((*cp)->baseminor + (*cp)->minorct > baseminor))) {
                ret = -EBUSY;
                goto out;
        }

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel