On Mon, 11 Sept 2023 at 09:46, Heinrich Schuchardt <heinrich.schuchardt@xxxxxxxxxxxxx> wrote: > > On 9/11/23 08:45, Ard Biesheuvel wrote: > > On Sun, 10 Sept 2023 at 22:42, Heinrich Schuchardt > > <heinrich.schuchardt@xxxxxxxxxxxxx> wrote: > >> > >> On 9/10/23 20:53, Anisse Astier wrote: > >>> Hi Heinrich, > >>> > >>> On Sun, Sep 10, 2023 at 06:54:45AM +0200, Heinrich Schuchardt wrote: > >>>> Some firmware (notably U-Boot) provides GetVariable() and > >>>> GetNextVariableName() but not QueryVariableInfo(). > >>> > >>> From a quick search, it seems u-boot, does support QueryVariableInfo, is > >>> it on a given version ? > >>> > >>> https://elixir.bootlin.com/u-boot/v2023.07.02/source/lib/efi_loader/efi_variable.c#L391 > >> > >> QueryVariableInfo() and SetVariable() are available before > >> ExitBootServices(), i.e. in Linux' EFI stub. > >> > >> ExitBootServices() results in calling efi_variables_boot_exit_notify() > >> which disables these services during the UEFI runtime. > >> > >>> > >>>> > >>>> With commit d86ff3333cb1 ("efivarfs: expose used and total size") the > >>>> statfs syscall was broken for such firmware. > >>> > >>> Could you be more specific ? What breaks, and what regressed ? I imagine > >>> it could be some scripts running df, but maybe you had something else in > >>> mind ? > >> > >> Some more details can be found in > >> https://bugs.launchpad.net/ubuntu/+source/linux-meta-riscv/+bug/2034705. > >> > >> Though EFI variables are exposed via GetVariable() and > >> GetNextVariableName() the efivar command refuses to display variables > >> when statfs() reports an error. > >> > >>> > >>>> > >>>> If QueryVariableInfo() does not exist or returns an error, just report the > >>>> file-system size as 0 as statfs_simple() previously did. > >>> > >>> I considered doing this [2] , but we settled on returning an error > >>> instead for clarity: > >>> https://lore.kernel.org/linux-efi/20230515-vorgaben-portrait-bb1b4255d31a@brauner/ > >>> > >>> I still think it would be a good idea if necessary. > >> > >> We should never break user APIs. > >> > > > > Indeed. > > > >>> > >>> On the approach, I prefer what Ard proposed, to fall back to the old > >>> approach. I think the difference in block size could also be a good > >>> marker that something wrong is happening: > >>> https://lore.kernel.org/linux-efi/CAMj1kXEkNSoqG4zWfCZ8Ytte5b2SzwXggZp21Xt17Pszd-q0dg@xxxxxxxxxxxxxx/ > >> > >> This will allow user code making assumptions based on block size: > >> If block size > 1, assume setting variables is possible. > >> > >> We should really avoid this. > >> > > > > I agree that having different block sizes depending on which code path > > is taken is not great. But that is the situation we are already in, > > given that older kernels will always report PAGE_SIZE. And actually, > > PAGE_SIZE does not make sense either - PAGE_SIZE could be larger than > > 4k on ARM for instance, so the efivarfs block size will be dependent > > on the page size of the kernel you happened to boot. > > > > So I think we should go with the below: > > > > --- a/fs/efivarfs/super.c > > +++ b/fs/efivarfs/super.c > > @@ -32,10 +32,16 @@ static int efivarfs_statfs(struct dentry *dentry, > > struct kstatfs *buf) > > u64 storage_space, remaining_space, max_variable_size; > > efi_status_t status; > > > > - status = efivar_query_variable_info(attr, &storage_space, > > &remaining_space, > > - &max_variable_size); > > - if (status != EFI_SUCCESS) > > - return efi_status_to_err(status); > > + /* Some UEFI firmware does not implement QueryVariableInfo() */ > > + storage_space = remaining_space = 0; > > + if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) { > > + status = efivar_query_variable_info(attr, &storage_space, > > + &remaining_space, > > + &max_variable_size); > > + if (status != EFI_SUCCESS && status != EFI_UNSUPPORTED) > > + pr_warn_ratelimited("query_variable_info() > > failed: 0x%lx\n", > > + status); > > Adding a warning here is helpful. The else branch would be: > > + } else { > + buf->f_blocks = storage_space; > + buf->f_bfree = remaining_space; > + } > The else branch is redundant if we leave the assignments of f_blocks and f_bfree where they were before.
