Re: [XenPPC] [PATCH] Booting xen_maple_defconfig kernel on bare hardware

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Jul 31, 2006, at 9:41 PM, Amos Waterland wrote:

> These patches allow 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.
>
> The 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.
good catch!

> Note that the preferred console system is subverted by Xen's  
> driver, in
> that it uses a value of -1 for index, which means that any ttySX in  
> the
> command line arguments will get Xen's tty driver.  See  
> register_console().
I'm not sure I understand this.. we set the preferred console in xen/ 
setup.c very early, _way_ before this console is registers so I'm not  
sure where the -1 helps you.
I do see that the actual index you _do_ get is returned in kcons- 
>index.  I wonder if you can use that to make a better guess at the  
first minor number.
> 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 };
Hmm, IMNSHO anonymous enum's have little or no value.

>  #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);
I guess the final patch will have a "proper" loop and won't be  
continuously alloc/put the driver?
>         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;
> +               }
> +
do we really want to stop at 8? why not stop at (1<<MINOR_BITS) and  
maybe increment by 4 or 8?

>                 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;
>         }
>
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