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Re: Grub2 almost does what I want

From: Andrey Borzenkov
Subject: Re: Grub2 almost does what I want
Date: Wed, 6 Feb 2013 06:56:07 +0400

В Tue, 5 Feb 2013 15:04:46 -0800
Jordan Uggla <address@hidden> пишет:

> On Sun, Feb 3, 2013 at 1:59 AM, Felix Miata <address@hidden> wrote:
> > On 2013-02-03 04:24 (GMT-0500) Felix Miata composed:
> >
> >
> >> On 2013-02-03 12:28 (GMT+0400) Andrey Borzenkov composed:
> >
> >
> >>> 02 Feb 2013 16:04:18 -0500 Felix Miata composed:
> >
> >
> >>>> 1-Get rid of the vga= is deprecated message. It has nothing to do with
> >>>> Grub2
> >>>> function.
> >
> >
> >>> No quite. From Documentation/kernel-parameters.txt:
> >
> >
> >>>                          This is actually a boot loader parameter; the
> >>> value is
> >>>                          passed to the kernel using a special protocol.
> >
> >
> >> Either that doc is wrong, or it serves more than one purpose....
> >
> >
> > On reflection I believe a third interpretation is the correct one, that is,
> > "passed to the kernel" confirms that it is a kernel parameter, which the
> > kernel can only acquire by virtue of its presence on cmdline, which makes it
> > a "boot loader parameter". That is not to say it gets used for the boot
> > loader's own function, because it isn't. The only thing the boot loader does
> > with it is provide it to the kernel for the kernel's use. Consequently, the
> > boot loader itself has no business complaining about its presence. It is not
> > a valid purpose of a bootloader to report suitability or not of a particular
> > kernel cmdline parameter to any particular kernel, even if one was known to
> > be deprecated, or even unsupported, when the boot loader was built.
> Your interpretation is completely incorrect. The kernel's
> documentation means exactly what it says, vga= is a parameter
> interpreted by the bootloader, which then switches to a given video
> mode before handing off to the kernel, and passes information about
> this mode via other means. 

Not quite. Bootloader may pass to kernel special value meaning "do not
do anything, leave mode as is"; if bootloader did pass actual VGA mode
value to kernel, it is kernel which sets the mode.

>                           The linux kernel does not interpret the
> vga= parameter, and if grub simply ignored it (but still passed it on
> as part of the linux cmdline) you would not get the desired effect.
> Since this is a parameter interpreted by the bootloader rather than
> the kernel it really doesn't make sense for it to be in the linux
> cmdline at all. That is why grub instead uses GRUB_GFXPAYLOAD (or
> $gfxpayload when working directly with a grub.cfg) as the means of
> telling grub what mode it should hand off to the kernel.
> GRUB_GFXPAYLOAD and $gfxpayload also take simple resolutions in
> readable strings like "1024x768x32" rather than arcane VESA mode
> numbers, making it even more appropriate to use. vga= is deprecated
> but (for now) is still handled by grub for backwards compatibility, it
> should not be used in new installations.

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