[1/1] efivarfs: fix statfs() on efivarfs

Some firmware (notably U-Boot) provides GetVariable() and
GetNextVariableName() but not QueryVariableInfo().

With commit d86ff3333cb1 ("efivarfs: expose used and total size") the
statfs syscall was broken for such firmware.

If QueryVariableInfo() does not exist or returns an error, just report the
file-system size as 0 as statfs_simple() previously did.

Fixes: d86ff3333cb1 ("efivarfs: expose used and total size")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
---
Tested on riscv64 StarFive VisionFive 2 with
Linux 6.5 and U-Boot v2023.10-rc4.
---
 fs/efivarfs/super.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

Hi Heinrich,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.5 next-20230908]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Heinrich-Schuchardt/efivarfs-fix-statfs-on-efivarfs/20230910-020949
base:   linus/master
patch link:    https://lore.kernel.org/r/20230909180812.10904-1-heinrich.schuchardt%40canonical.com
patch subject: [PATCH 1/1] efivarfs: fix statfs() on efivarfs
config: riscv-randconfig-r003-20230910 (https://download.01.org/0day-ci/archive/20230910/202309100610.zLYrHmqr-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project.git f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230910/202309100610.zLYrHmqr-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309100610.zLYrHmqr-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> fs/efivarfs/super.c:45:6: warning: variable 'remaining_space' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
           if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   fs/efivarfs/super.c:60:6: note: uninitialized use occurs here
           if (remaining_space > efivar_reserved_space())
               ^~~~~~~~~~~~~~~
   fs/efivarfs/super.c:45:2: note: remove the 'if' if its condition is always true
           if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   fs/efivarfs/super.c:32:36: note: initialize the variable 'remaining_space' to silence this warning
           u64 storage_space, remaining_space, max_variable_size;
                                             ^
                                              = 0
   1 warning generated.


vim +45 fs/efivarfs/super.c

    26	
    27	static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
    28	{
    29		const u32 attr = EFI_VARIABLE_NON_VOLATILE |
    30				 EFI_VARIABLE_BOOTSERVICE_ACCESS |
    31				 EFI_VARIABLE_RUNTIME_ACCESS;
    32		u64 storage_space, remaining_space, max_variable_size;
    33		efi_status_t status;
    34	
    35		/*
    36		 * This is not a normal filesystem, so no point in pretending it has a block
    37		 * size; we declare f_bsize to 1, so that we can then report the exact value
    38		 * sent by EFI QueryVariableInfo in f_blocks and f_bfree
    39		 */
    40		buf->f_bsize	= 1;
    41		buf->f_namelen	= NAME_MAX;
    42		buf->f_type	= dentry->d_sb->s_magic;
    43	
    44		/* Some UEFI firmware does not implement QueryVariable() */
  > 45		if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
    46			status = efivar_query_variable_info(attr, &storage_space,
    47							    &remaining_space,
    48							    &max_variable_size);
    49			if (status == EFI_SUCCESS) {
    50				buf->f_blocks	= storage_space;
    51				buf->f_bfree	= remaining_space;
    52			}
    53		}
    54	
    55		/*
    56		 * In f_bavail we declare the free space that the kernel will allow writing
    57		 * when the storage_paranoia x86 quirk is active. To use more, users
    58		 * should boot the kernel with efi_no_storage_paranoia.
    59		 */
    60		if (remaining_space > efivar_reserved_space())
    61			buf->f_bavail = remaining_space - efivar_reserved_space();
    62		else
    63			buf->f_bavail = 0;
    64	
    65		return 0;
    66	}
    67	static const struct super_operations efivarfs_ops = {
    68		.statfs = efivarfs_statfs,
    69		.drop_inode = generic_delete_inode,
    70		.evict_inode = efivarfs_evict_inode,
    71	};
    72