Messages in this thread | | | Date | Sun, 10 Sep 2023 22:43:50 +0200 | Subject | Re: [PATCH v2 1/1] efivarfs: fix statfs() on efivarfs | From | Heinrich Schuchardt <> |
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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.
> > 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@mail.gmail.com/
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.
Best regards
Heinrich
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