commit 68d92986 upstream.

UEFI variables are typically stored in flash. For various reasons, avaiable
space is typically not reclaimed immediately upon the deletion of a
variable - instead, the system will garbage collect during initialisation
after a reboot.

Some systems appear to handle this garbage collection extremely poorly,
failing if more than 50% of the system flash is in use. This can result in
the machine refusing to boot. The safest thing to do for the moment is to
forbid writes if they'd end up using more than half of the storage space.
We can make this more finegrained later if we come up with a method for
identifying the broken machines.
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
[bwh: Backported to 3.2:
 - Drop efivarfs changes and unused check_var_size()
 - Add error codes to include/linux/efi.h, added upstream by
   commit 5d9db883 ('efi: Add support for a UEFI variable filesystem')
 - Add efi_status_to_err(), added upstream by commit 7253eaba
   ('efivarfs: Return an error if we fail to read a variable')]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>