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SubjectRe: [PATCH] CON_CONSDEV bit not set correctly on last console
On Wed, Apr 06, 2005 at 03:53:17PM -0700, Andrew Morton wrote:
| Greg Edwards <edwardsg@sgi.com> wrote:
| >
| > According to include/linux/console.h, CON_CONSDEV flag should be set on
| > the last console specified on the boot command line:
| >
| > 86 #define CON_PRINTBUFFER (1)
| > 87 #define CON_CONSDEV (2) /* Last on the command line */
| > 88 #define CON_ENABLED (4)
| > 89 #define CON_BOOT (8)
| >
| > This does not currently happen if there is more than one console specified
| > on the boot commandline. Instead, it gets set on the first console on the
| > command line. This can cause problems for things like kdb that look for
| > the CON_CONSDEV flag to see if the console is valid.
| >
| > Additionaly, it doesn't look like CON_CONSDEV is reassigned to the next
| > preferred console at unregister time if the console being unregistered
| > currently has that bit set.
| >
| > Example (from sn2 ia64):
| >
| > elilo vmlinuz root=<dev> console=ttyS0 console=ttySG0
| >
| > in this case, the flags on ttySG console struct will be 0x4 (should be
| > 0x6).
| >
| > Attached patch against bk fixes both issues for the cases I looked at. It
| > uses selected_console (which gets incremented for each console specified
| > on the command line) as the indicator of which console to set CON_CONSDEV
| > on. When adding the console to the list, if the previous one had
| > CON_CONSDEV set, it masks it out. Tested on ia64 and x86.
|
| The `console=a console=b' behaviour seem basically random to me :(. And it
| gets re-randomised on a regular basis.
|
| I wonder if we should leave the existing behaviour alone (continue to set
| CON_CONSDEV on the first console) and just change the documentation?
| That'll minimise the disruption which we cause.

The problem with the current behavior is it breaks overriding the default
from the boot line. In the ia64 case, there may be a global append line
defining console=a in elilo.conf. Then you want to boot your kernel, and
want to override the default by passing console=b on the boot line.
elilo constructs the kernel cmdline by starting with the value of the
global append line, then tacks on whatever else you specify, which puts
console=b last.

You can always edit the elilo.conf and change the global value, but that
seems like a pretty big hammer for something you may just want to test.

Greg
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