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References: <20230426195853.633233-1-anisse@astier.eu>
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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Wed, 10 May 2023 17:13:36 +0200
Message-ID: <CAMj1kXE2-76KZDxpHBPcZgbB8vGDmLEbiRGmw_5o-rsNzT9oQw@mail.gmail.com>
Subject: Re: [PATCH] efivarfs: expose used and total size
To:     Anisse Astier <anisse@astier.eu>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christian Brauner <brauner@kernel.org>
Cc:     linux-efi@vger.kernel.org, Johan Hovold <johan+linaro@kernel.org>,
        Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Jeremy Kerr <jk@ozlabs.org>,
        platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org,
        Anisse Astier <an.astier@criteo.com>
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On Wed, 26 Apr 2023 at 21:59, Anisse Astier <anisse@astier.eu> wrote:
>
> From: Anisse Astier <an.astier@criteo.com>
>
> When writing 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 conventionnal filesystem, block size is
> intentionnally set to 1 instead of PAGE_SIZE.
>
> x86 quirks of reserved size are taken into account and available and
> free size can be different, further helping debugging space issues.
>

I have no objections to this, but I'm not much of a user space/ VFS
person, so adding some other folks that can chime in if they want.

The point of this patch is that user space can query this information
using statvfs(), right?


> Signed-off-by: Anisse Astier <an.astier@criteo.com>
> ---
> Notes:
> Patch isn't split per subsystem intentionally, for better understanding
> of intent; split could be trivial in a later version.
>
> I'm not sure whether statfs(2) should return an error if the efi request
> fails; I think it could be ignored with maybe a WARN_ONCE; which would
> be close to the current behaviour.
>
> Regards,
>
> Anisse
>
> ---
>  arch/x86/platform/efi/quirks.c |  8 ++++++++
>  drivers/firmware/efi/efi.c     |  1 +
>  drivers/firmware/efi/vars.c    | 12 ++++++++++++
>  fs/efivarfs/super.c            | 26 +++++++++++++++++++++++++-
>  include/linux/efi.h            | 10 ++++++++++
>  5 files changed, 56 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index b0b848d6933a..587fa51230e2 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 efi_reserved_space(void)
> +{
> +       if (efi_no_storage_paranoia)
> +               return 0;
> +       return EFI_MIN_RESERVE;
> +}
> +EXPORT_SYMBOL_GPL(efi_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
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index abeff7dc0b58..d0dfa007bffc 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -211,6 +211,7 @@ static int generic_ops_register(void)
>         generic_ops.get_variable = efi.get_variable;
>         generic_ops.get_next_variable = efi.get_next_variable;
>         generic_ops.query_variable_store = efi_query_variable_store;
> +       generic_ops.query_variable_info = efi.query_variable_info;
>
>         if (efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE)) {
>                 generic_ops.set_variable = efi.set_variable;
> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index bd75b87f5fc1..c5382d5c3073 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -245,3 +245,15 @@ efi_status_t efivar_set_variable(efi_char16_t *name, efi_guid_t *vendor,
>         return status;
>  }
>  EXPORT_SYMBOL_NS_GPL(efivar_set_variable, EFIVAR);
> +
> +efi_status_t efivar_query_variable_info(u32 attr,
> +                                       u64 *storage_space,
> +                                       u64 *remaining_space,
> +                                       u64 *max_variable_size)
> +{
> +       if (!__efivars->ops->query_variable_info)
> +               return EFI_UNSUPPORTED;
> +       return __efivars->ops->query_variable_info(attr, storage_space,
> +                       remaining_space, max_variable_size);
> +}
> +EXPORT_SYMBOL_NS_GPL(efivar_query_variable_info, EFIVAR);
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index 482d612b716b..064bfc0243c9 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -13,6 +13,7 @@
>  #include <linux/ucs2_string.h>
>  #include <linux/slab.h>
>  #include <linux/magic.h>
> +#include <linux/statfs.h>
>
>  #include "internal.h"
>
> @@ -23,8 +24,31 @@ static void efivarfs_evict_inode(struct inode *inode)
>         clear_inode(inode);
>  }
>
> +static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
> +{
> +       u64 storage_space, remaining_space, max_variable_size;
> +       efi_status_t status;
> +       const u32 attr = (EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
> +        EFI_VARIABLE_RUNTIME_ACCESS);
> +
> +       buf->f_type = dentry->d_sb->s_magic;
> +       buf->f_bsize = 1;
> +       buf->f_namelen = NAME_MAX;
> +
> +       status = efivar_query_variable_info(attr, &storage_space, &remaining_space,
> +                                           &max_variable_size);
> +       if (status != EFI_SUCCESS)
> +               return efi_status_to_err(status);
> +       buf->f_blocks = storage_space;
> +       buf->f_bfree = remaining_space;
> +       if (remaining_space > efi_reserved_space())
> +               buf->f_bavail = remaining_space - efi_reserved_space();
> +       else
> +               buf->f_bavail = 0;
> +       return 0;
> +}
>  static const struct super_operations efivarfs_ops = {
> -       .statfs = simple_statfs,
> +       .statfs = efivarfs_statfs,
>         .drop_inode = generic_delete_inode,
>         .evict_inode = efivarfs_evict_inode,
>  };
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 7aa62c92185f..d2b686191870 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -703,6 +703,7 @@ static inline void efi_enter_virtual_mode (void) {}
>  extern efi_status_t efi_query_variable_store(u32 attributes,
>                                              unsigned long size,
>                                              bool nonblocking);
> +extern u64 efi_reserved_space(void);
>  #else
>
>  static inline efi_status_t efi_query_variable_store(u32 attributes,
> @@ -711,6 +712,10 @@ static inline efi_status_t efi_query_variable_store(u32 attributes,
>  {
>         return EFI_SUCCESS;
>  }
> +static inline u64 efi_reserved_space(void)
> +{
> +       return 0;
> +}
>  #endif
>  extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
>
> @@ -1042,6 +1047,7 @@ 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 {
> @@ -1087,6 +1093,10 @@ 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);
>
> --
> 2.34.1
>