[patch 1/3 v2] Add function get_bootparam

[H. Peter Anvin]

On 11/11/2013 05:27 PM, Toshi Kani wrote:
> On Tue, 2013-11-05 at 16:29 +0800, dyoung at redhat.com wrote:
>> Not only setup_subarch will get data from debugfs file
>> boot_params/data, later code for adding efi_info will
>> also need do same thing. Thus add a common function here
>> for later use.
> 
> get_bootparam() calls find_mnt_by_fsname("debugfs"), which assumes that
> debugfs is mounted with device name "debugfs".  This function fails
> when:
>  - debugfs is not mounted, or
>  - debugfs is mounted with a different device name, such as nodev [1].
> 
> This issue is not introduced by this patch.  But the original code,
> which sets hardware_subarch, seems to work even if it failed to access
> debugfs (which is ignored) since hardware_subarch is zero most of the
> cases anyway.  With this change, however, this failure now makes the 2nd
> kernel unbootable.  So, it needs to be addressed to make this code path
> work reliably (or kexec should fail at least).
> 

Greg, Ingo,

Since there is now a legitimate user of this stuff, can we actually
export this in sysfs (or something else other than sploit^Wdebugfs)?

kexec-tools can have a fallback to debugfs if we really need it, but
making people mount debugfs to have some essential piece of
functionality scares the heck out of me.

	-hpa