efivarfs: expose used and total size

When writing EFI variables, one might get errors with no other message
on why it fails. Being able to see how much is used by EFI variables
helps analyzing such issues.

Since this is not a conventional filesystem, block size is intentionally
set to 1 instead of PAGE_SIZE.

x86 quirks of reserved size are taken into account; so that available
and free size can be different, further helping debugging space issues.

With this patch, one can see the remaining space in EFI variable storage
via efivarfs, like this:

   $ df -h /sys/firmware/efi/efivars/
   Filesystem      Size  Used Avail Use% Mounted on
   efivarfs        176K  106K   66K  62% /sys/firmware/efi/efivars

Signed-off-by: Anisse Astier <an.astier@criteo.com>
[ardb: - rename efi_reserved_space() to efivar_reserved_space()
       - whitespace/coding style tweaks]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index b0b848d6933a..f0cc00032751 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -114,6 +114,14 @@ void efi_delete_dummy_variable(void)
 				     EFI_VARIABLE_RUNTIME_ACCESS, 0, NULL);
 }
 
+u64 efivar_reserved_space(void)
+{
+	if (efi_no_storage_paranoia)
+		return 0;
+	return EFI_MIN_RESERVE;
+}
+EXPORT_SYMBOL_GPL(efivar_reserved_space);
+
 /*
  * In the nonblocking case we do not attempt to perform garbage
  * collection if we do not have enough free space. Rather, we do the