[PATCH] partitions/efi: complete gpt kernel param purpose

[PATCH] partitions/efi: complete gpt kernel param purpose

[Davidlohr Bueso]

From: Davidlohr Bueso <davidlohr@hp.com>

The usage of the 'gpt' kernel parameter is twofold:
(i) skip any mbr integrity checks and (ii) enable the
backup GPT header to be used in situations where the
primary one is corrupted. This last "feature" is not
obvious and needs to be properly documented in the
kernel-parameters document.

References: https://bugzilla.kernel.org/show_bug.cgi?id=63591
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
---
 Documentation/kernel-parameters.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 50680a5..1e353a4 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1013,7 +1013,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			debugfs files are removed at module unload time.
 
 	gpt		[EFI] Forces disk with valid GPT signature but
-			invalid Protective MBR to be treated as GPT.
+			invalid Protective MBR to be treated as GPT. If the
+			primary GPT is corrupted, it enables the backup/alternate
+			GPT to be used instead.
 
 	grcan.enable0=	[HW] Configuration of physical interface 0. Determines
 			the "Enable 0" bit of the configuration register.
-- 
1.8.1.4

Re: [PATCH] partitions/efi: complete gpt kernel param purpose

[Karel Zak]

On Wed, Dec 04, 2013 at 03:16:02PM -0800, Davidlohr Bueso wrote:
> From: Davidlohr Bueso <davidlohr@hp.com>
> 
> The usage of the 'gpt' kernel parameter is twofold:
> (i) skip any mbr integrity checks and (ii) enable the
> backup GPT header to be used in situations where the
> primary one is corrupted. This last "feature" is not
> obvious and needs to be properly documented in the
> kernel-parameters document.

The question is if we really have to force users to specify "gpt"
kernel parameter to use the backup GPT header. Maybe it would be
enough to report the problem (print warning) and use the valid backup
header. IMHO the current behaviour is overkill.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: [PATCH] partitions/efi: complete gpt kernel param purpose

[Davidlohr Bueso]

On Thu, 2013-12-05 at 12:21 +0100, Karel Zak wrote:
> On Wed, Dec 04, 2013 at 03:16:02PM -0800, Davidlohr Bueso wrote:
> > From: Davidlohr Bueso <davidlohr@hp.com>
> > 
> > The usage of the 'gpt' kernel parameter is twofold:
> > (i) skip any mbr integrity checks and (ii) enable the
> > backup GPT header to be used in situations where the
> > primary one is corrupted. This last "feature" is not
> > obvious and needs to be properly documented in the
> > kernel-parameters document.
> 
> The question is if we really have to force users to specify "gpt"
> kernel parameter to use the backup GPT header. Maybe it would be
> enough to report the problem (print warning) and use the valid backup
> header. IMHO the current behaviour is overkill.

Well yes, however, the rationale behind having to use 'gpt' is to
protect against devices which misreport their size, and forces the user
to decide to use the alternate GPT when they still have a valid primary
header. This has been the policy for years.

Thanks,
Davidlohr