linux-kernel - Re: [PATCH 1/2] efivars: Check max

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Date:	Thu, 04 Apr 2013 18:12:39 +0200
From:	Richard Weinberger <richard@....at>
To:	"Luck, Tony" <tony.luck@...el.com>
CC:	"Fleming, Matt" <matt.fleming@...el.com>,
	"cbouatmailru@...il.com" <cbouatmailru@...il.com>,
	"ccross@...roid.com" <ccross@...roid.com>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"matthew.garrett@...ula.com" <matthew.garrett@...ula.com>
Subject: Re: [PATCH 1/2] efivars: Check max_size only if it is non-zero.

Am 04.04.2013 18:00, schrieb Luck, Tony:
>> Some (broken?) EFI implementations return always a MaximumVariableSize of 0,
>> check against max_size only if it is non-zero.
>
> The spec doesn't say that zero has any special meaning - so if an implementation
> returns max_size == 0 but lets you set a variable to a size > 0, then I don't think
> there is a need for parentheses or a "?" in this commit comment.

Thanks for the clarification.
Yesterday I've looked into the spec, but the >2000 pages hurt my brain. ;-)

> But if Linux silently accepts such broken EFI, then there is no feedback loop
> to let EFI implementations know that they are broken.  In other areas we have
> thrown out messages about firmware being broken ... perhaps:
>
> 	if (max_size == 0)
> 		printk_once("Broken EFI implementation is returning MaxVariableSize=0\n");
>
> would help? After all there probably *is* a maximum size - but EFI isn't telling us what it is.

Fair point. I'll add such a printk() to my patch and resend.

Thanks,
//richard

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