Re: [edk2-devel] [PATCH 12/13] OvmfPkg/QemuKernelLoaderFsDxe: add support for new Linux initrd device path

["Laszlo Ersek" <lersek@redhat.com>]

On 03/02/20 08:29, Ard Biesheuvel wrote:
> Linux v5.7 will introduce a new method to load the initial ramdisk
> (initrd) from the loader, using the LoadFile2 protocol installed on a
> special vendor GUIDed media device path.
> 
> Add support for this to our QEMU command line kernel/initrd loader.
> 
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2566
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c   | 79 ++++++++++++++++++++
>  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf |  2 +
>  2 files changed, 81 insertions(+)
> 
> diff --git a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> index 77d8fedb738a..415946edf22a 100644
> --- a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> +++ b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> @@ -13,15 +13,18 @@
>  #include <Guid/FileInfo.h>
>  #include <Guid/FileSystemInfo.h>
>  #include <Guid/FileSystemVolumeLabelInfo.h>
> +#include <Guid/LinuxEfiInitrdMedia.h>
>  #include <Guid/QemuKernelLoaderFsMedia.h>
>  #include <Library/BaseLib.h>
>  #include <Library/BaseMemoryLib.h>
>  #include <Library/DebugLib.h>
> +#include <Library/DevicePathLib.h>
>  #include <Library/MemoryAllocationLib.h>
>  #include <Library/QemuFwCfgLib.h>
>  #include <Library/UefiBootServicesTableLib.h>
>  #include <Library/UefiRuntimeServicesTableLib.h>
>  #include <Protocol/DevicePath.h>
> +#include <Protocol/LoadFile2.h>
>  #include <Protocol/SimpleFileSystem.h>
>  
>  //
> @@ -84,6 +87,19 @@ STATIC CONST SINGLE_VENMEDIA_NODE_DEVPATH mFileSystemDevicePath = {
>    }
>  };
>  
> +STATIC CONST SINGLE_VENMEDIA_NODE_DEVPATH mInitrdDevicePath = {
> +  {
> +    {
> +      MEDIA_DEVICE_PATH, MEDIA_VENDOR_DP,
> +      { sizeof (VENDOR_DEVICE_PATH) }
> +    },
> +    LINUX_EFI_INITRD_MEDIA_GUID
> +  }, {
> +    END_DEVICE_PATH_TYPE, END_ENTIRE_DEVICE_PATH_SUBTYPE,
> +    { sizeof (EFI_DEVICE_PATH_PROTOCOL) }
> +  }
> +};
> +
>  //
>  // The "file in the EFI stub filesystem" abstraction.
>  //
> @@ -839,6 +855,48 @@ STATIC CONST EFI_SIMPLE_FILE_SYSTEM_PROTOCOL mFileSystem = {
>    StubFileSystemOpenVolume
>  };
>  
> +STATIC
> +EFI_STATUS
> +EFIAPI
> +InitrdLoadFile2 (
> +  IN EFI_LOAD_FILE2_PROTOCOL          *This,
> +  IN EFI_DEVICE_PATH_PROTOCOL         *FilePath,
> +  IN BOOLEAN                          BootPolicy,
> +  IN OUT UINTN                        *BufferSize,
> +  IN VOID                             *Buffer OPTIONAL
> +  )
> +{
> +  CONST KERNEL_BLOB   *InitrdBlob = &mKernelBlob[KernelBlobTypeInitrd];
> +
> +  ASSERT (InitrdBlob->Size > 0);
> +
> +  if (BootPolicy) {
> +    return EFI_UNSUPPORTED;
> +  }
> +
> +  if (BufferSize == NULL || !IsDevicePathValid (FilePath, 0)) {
> +    return EFI_INVALID_PARAMETER;
> +  }
> +
> +  if (FilePath->Type != END_DEVICE_PATH_TYPE ||
> +      FilePath->SubType != END_ENTIRE_DEVICE_PATH_SUBTYPE) {
> +    return EFI_NOT_FOUND;
> +  }
> +
> +  if (Buffer == NULL || *BufferSize < InitrdBlob->Size) {
> +    *BufferSize = InitrdBlob->Size;
> +    return EFI_BUFFER_TOO_SMALL;
> +  }
> +
> +  CopyMem (Buffer, InitrdBlob->Data, InitrdBlob->Size);
> +
> +  *BufferSize = InitrdBlob->Size;
> +  return EFI_SUCCESS;
> +}
> +
> +STATIC CONST EFI_LOAD_FILE2_PROTOCOL     mInitrdLoadFile2 = {
> +  InitrdLoadFile2,
> +};
>  
>  //
>  // Utility functions.
> @@ -945,6 +1003,7 @@ QemuKernelLoaderFsDxeEntrypoint (
>    KERNEL_BLOB               *KernelBlob;
>    EFI_STATUS                Status;
>    EFI_HANDLE                FileSystemHandle;
> +  EFI_HANDLE                InitrdLoadFile2Handle;
>  
>    if (!QemuFwCfgIsAvailable ()) {
>      return EFI_NOT_FOUND;
> @@ -989,8 +1048,28 @@ QemuKernelLoaderFsDxeEntrypoint (
>      goto FreeBlobs;
>    }
>  
> +  if (KernelBlob[KernelBlobTypeInitrd].Size > 0) {
> +    InitrdLoadFile2Handle = NULL;
> +    Status = gBS->InstallMultipleProtocolInterfaces (&InitrdLoadFile2Handle,
> +                    &gEfiDevicePathProtocolGuid,  &mInitrdDevicePath,
> +                    &gEfiLoadFile2ProtocolGuid,   &mInitrdLoadFile2,
> +                    NULL);
> +    if (EFI_ERROR (Status)) {
> +      DEBUG ((DEBUG_ERROR, "%a: InstallMultipleProtocolInterfaces(): %r\n",
> +        __FUNCTION__, Status));
> +      goto UninstallFileSystemHandle;
> +    }
> +  }
> +
>    return EFI_SUCCESS;
>  
> +UninstallFileSystemHandle:
> +  Status = gBS->UninstallMultipleProtocolInterfaces (FileSystemHandle,
> +                  &gEfiDevicePathProtocolGuid,       &mFileSystemDevicePath,
> +                  &gEfiSimpleFileSystemProtocolGuid, &mFileSystem,
> +                  NULL);
> +  ASSERT_EFI_ERROR (Status);
> +
>  FreeBlobs:
>    while (BlobType > 0) {
>      CurrentBlob = &mKernelBlob[--BlobType];
> diff --git a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf
> index f4b50c265027..737f9b87a7c7 100644
> --- a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf
> +++ b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.inf
> @@ -28,6 +28,7 @@ [LibraryClasses]
>    BaseLib
>    BaseMemoryLib
>    DebugLib
> +  DevicePathLib
>    MemoryAllocationLib
>    UefiBootServicesTableLib
>    QemuFwCfgLib
> @@ -42,6 +43,7 @@ [Guids]
>  
>  [Protocols]
>    gEfiDevicePathProtocolGuid                ## PRODUCES
> +  gEfiLoadFile2ProtocolGuid                 ## PRODUCES
>    gEfiSimpleFileSystemProtocolGuid          ## PRODUCES
>  
>  [Depex]
> 

I think this patch conflicts with your other patch:

  [edk2-devel] [PATCH v3 2/6] OvmfPkg: add 'initrd' shell command to
                              expose Linux initrd via device path

There should not be two different handles in the handle database that
carry the same device path (I mean "same device path" by contents, not
by reference).

I believe that it's possible that the command-line specified -kernel /
-initrd are attempted first, but the kernel's stub returns for some
reason. Then the user can still go to the UEFI shell, and use the new
dynamic shell command. In that case I think the device path will cease
being unique (by contents).

I think you can solve this as follows:

- in both modules (this driver, and the dynamic shell command driver),
install a NULL protocol interface with GUID = gEfiCallerIdGuid on the
same handle that carries the device path and LoadFile2

- in both modules, before you touch the handle that carries the device
path, try to locate it first. If it exists but doesn't carry the subject
module's FILE_GUID as a NULL protocol interface, we know the device path
was created by the "other" module, and we can bail.

Just an idea.

Thanks,
Laszlo

Thanks
Laszlo