Messages in this thread | | | Date | Wed, 12 Dec 2007 11:05:45 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH -mm -v2] x86 boot : export boot_params via sysfs |
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Greg KH wrote: >> This is a binary structure defined by protocol; > > What protocol? Is this a "standard" documented somewhere?
Yes, see Documentation/i386/* (although some of it is documented by reference to include/asm-x86/boot_params.h).
>> in that way it's not significantly different from something passed >> from the firmware (in fact, it might very well *be* passed from the >> firmware.) We have in the past found platform bugs by looking at the >> contents of the whole structure, e.g. to find that part of it has >> been inappropriately clobbered. > > For debugging things, then just export it through debugfs.
Fair enough, however...
>> It is also in the form needed by e.g. kexec to operate. > > Does kexec need this today to work properly? Or is this something new?
I believe kexec currently tries to reconstitute it from what data is available to it. This is incomplete, though, and has been flagged as a problem for kexec.
> What userspace program is going to know the exact data format of this > blob, and where is it going to know that format from? The kernel header > files in sanitized form? Or something else?
It can pick it up from <asm/boot_params.h> (which is now userspace-safe); or it can decode it itself. Programs like kexec can pass through most of the data without examining it, this is the main reason for having it as a blob.
-hpa
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