Re: [uml-devel] [patch 094/241] uml: fix error output during early boot

Re: [uml-devel] [patch 094/241] uml: fix error output during early boot

[Blaisorblade]

On Saturday 10 February 2007 10:44, akpm@linux-foundation.org wrote:
> From: Jeff Dike <jdike@addtoit.com>
>
> The startup code panics a lot if anything goes wrong early on.  This is
> wrong for several reasons, like the kernel isn't running, so you can't
> really be calling into it yet, but the harm comes from useful error
> messages being trapped in the printk ring where no one will ever see them.
>
> This patch changes these panics to perror and printf in wrappers which also
> exit.  Normal, informational, prints are also wrapped so that
> fflush(stdout) is called after each one.  This is so the output appears in
> the correct sequence in the event of an error.

libc's printf has an enormous stack usage, so that my_printf is used for 
direct output instead of printf; if this is ok because it's bootup code, then 
*fatal* should be marked as "bootup code only"; otherwise we may reuse 
vsprintf() and write() or fputs(); this should match what happens in 
my_printf, to avoid any unlikely problem with libc's buffering.
-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
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Re: [uml-devel] [patch 094/241] uml: fix error output during early boot

[Jeff Dike]

On Sat, Feb 10, 2007 at 01:31:20PM +0100, Blaisorblade wrote:
> libc's printf has an enormous stack usage, so that my_printf is used for 
> direct output instead of printf; if this is ok because it's bootup
> code, 

It is bootup code only.

> then *fatal* should be marked as "bootup code only"; 

OK.

> otherwise
> we may reuse vsprintf() and write() or fputs(); this should match
> what happens in my_printf, to avoid any unlikely problem with libc's
> buffering. 

Offhand, I would say that if we are on a kernel stack, printk is safe
to use, and should be used, so there's no need for things like
my_printf.  Maybe there are some exceptions in early boot when the
kernel is running, but before the console is working, but I can't
think of any problems we've had like that.

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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Re: [uml-devel] [patch 094/241] uml: fix error output during early boot

[Blaisorblade]

On Saturday 10 February 2007 23:21, Jeff Dike wrote:
> On Sat, Feb 10, 2007 at 01:31:20PM +0100, Blaisorblade wrote:
> > libc's printf has an enormous stack usage, so that my_printf is used for
> > direct output instead of printf; if this is ok because it's bootup
> > code,
>
> It is bootup code only.
>
> > then *fatal* should be marked as "bootup code only";
>
> OK.
>
> > otherwise
> > we may reuse vsprintf() and write() or fputs(); this should match
> > what happens in my_printf, to avoid any unlikely problem with libc's
> > buffering.
>
> Offhand, I would say that if we are on a kernel stack, printk is safe
> to use, and should be used, so there's no need for things like
> my_printf.  Maybe there are some exceptions in early boot when the
> kernel is running, but before the console is working, but I can't
> think of any problems we've had like that.

It's for no_config_chan (don't recall the right name), i.e. for when the 
console will never work because of a misconfiguration. Indeed it's static 
(and otherwise it ought to have a better name!).

-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
 http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com 


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