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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