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, 11 insertions, 0 deletions

diff --git a/include/linux/efi.h b/include/linux/efi.h
index 7aa62c92185f..bed3c92cbc31 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1042,6 +1042,7 @@ struct efivar_operations {
 	efi_set_variable_t *set_variable;
 	efi_set_variable_t *set_variable_nonblocking;
 	efi_query_variable_store_t *query_variable_store;
+	efi_query_variable_info_t *query_variable_info;
 };
 
 struct efivars {
@@ -1049,6 +1050,12 @@ struct efivars {
 	const struct efivar_operations *ops;
 };
 
+#ifdef CONFIG_X86
+u64 __attribute_const__ efivar_reserved_space(void);
+#else
+static inline u64 efivar_reserved_space(void) { return 0; }
+#endif
+
 /*
  * The maximum size of VariableName + Data = 1024
  * Therefore, it's reasonable to save that much
@@ -1087,6 +1094,10 @@ efi_status_t efivar_set_variable_locked(efi_char16_t *name, efi_guid_t *vendor,
 efi_status_t efivar_set_variable(efi_char16_t *name, efi_guid_t *vendor,
 				 u32 attr, unsigned long data_size, void *data);
 
+efi_status_t efivar_query_variable_info(u32 attr, u64 *storage_space,
+					u64 *remaining_space,
+					u64 *max_variable_size);
+
 #if IS_ENABLED(CONFIG_EFI_CAPSULE_LOADER)
 extern bool efi_capsule_pending(int *reset_type);