[efi] Add our own EFI_LOAD_FILE_PROTOCOL implementation

When iPXE is used as a UEFI driver, the UEFI PXE base code currently
provides the TCP/IP stack, network protocols, and user interface.
This represents a substantial downgrade from the standard BIOS iPXE
user experience.

Fix by installing our own EFI_LOAD_FILE_PROTOCOL implementation which
initiates the standard iPXE boot procedure.  This upgrades the UEFI
iPXE user experience to match the standard BIOS iPXE user experience.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/efi/efi_snp.h

 #include <ipxe/efi/Protocol/DevicePath.h>
 #include <ipxe/efi/Protocol/HiiConfigAccess.h>
 #include <ipxe/efi/Protocol/HiiDatabase.h>
+#include <ipxe/efi/Protocol/LoadFile.h>
 
 /** An SNP device */
 struct efi_snp_device {
 	EFI_NETWORK_INTERFACE_IDENTIFIER_PROTOCOL nii;
 	/** Component name protocol */
 	EFI_COMPONENT_NAME2_PROTOCOL name2;
+	/** Load file protocol handle */
+	EFI_LOAD_FILE_PROTOCOL load_file;
 	/** HII configuration access protocol */
 	EFI_HII_CONFIG_ACCESS_PROTOCOL hii;
 	/** HII package list */

src/interface/efi/efi_snp.c

 #include <ipxe/efi/efi_strings.h>
 #include <ipxe/efi/efi_snp.h>
 #include <config/general.h>
+#include <usr/autoboot.h>
 
 /** EFI simple network protocol GUID */
 static EFI_GUID efi_simple_network_protocol_guid
 	{ 0xBC, 0x81, 0x76, 0x7F, 0x1F, 0x97, 0x7A, 0x89 }
 };
 
-/** EFI component name protocol */
+/** EFI component name protocol GUID */
 static EFI_GUID efi_component_name2_protocol_guid
 	= EFI_COMPONENT_NAME2_PROTOCOL_GUID;
 
+/** EFI load file protocol GUID */
+static EFI_GUID efi_load_file_protocol_guid
+	= EFI_LOAD_FILE_PROTOCOL_GUID;
+
 /** List of SNP devices */
 static LIST_HEAD ( efi_snp_devices );
 
 	return 0;
 }
 
+/******************************************************************************
+ *
+ * Load file protocol
+ *
+ ******************************************************************************
+ */
+
+/**
+ * Load file
+ *
+ * @v loadfile		Load file protocol
+ * @v path		File path
+ * @v booting		Loading as part of a boot attempt
+ * @ret efirc		EFI status code
+ */
+static EFI_STATUS EFIAPI
+efi_snp_load_file ( EFI_LOAD_FILE_PROTOCOL *load_file,
+		    EFI_DEVICE_PATH_PROTOCOL *path __unused,
+		    BOOLEAN booting, UINTN *len __unused,
+		    VOID *data __unused ) {
+	struct efi_snp_device *snpdev =
+		container_of ( load_file, struct efi_snp_device, load_file );
+	struct net_device *netdev = snpdev->netdev;
+
+	/* Fail unless this is a boot attempt */
+	if ( ! booting ) {
+		DBGC ( snpdev, "SNPDEV %p cannot load non-boot file\n",
+		       snpdev );
+		return EFI_UNSUPPORTED;
+	}
+
+	/* Boot from network device */
+	ipxe ( netdev );
+
+	/* Assume boot process was aborted */
+	return EFI_ABORTED;
+}
+
+/** Load file protocol */
+static EFI_LOAD_FILE_PROTOCOL efi_snp_load_file_protocol = {
+	.LoadFile	= efi_snp_load_file,
+};
+
 /******************************************************************************
  *
  * iPXE network driver
 	snpdev->name2.GetControllerName = efi_snp_get_controller_name;
 	snpdev->name2.SupportedLanguages = "en";
 
+	/* Populate the load file protocol structure */
+	memcpy ( &snpdev->load_file, &efi_snp_load_file_protocol,
+		 sizeof ( snpdev->load_file ) );
+
 	/* Populate the device name */
 	efi_snprintf ( snpdev->name, ( sizeof ( snpdev->name ) /
 				       sizeof ( snpdev->name[0] ) ),
 			&efi_nii_protocol_guid, &snpdev->nii,
 			&efi_nii31_protocol_guid, &snpdev->nii,
 			&efi_component_name2_protocol_guid, &snpdev->name2,
+			&efi_load_file_protocol_guid, &snpdev->load_file,
 			NULL ) ) != 0 ) {
 		DBGC ( snpdev, "SNPDEV %p could not install protocols: "
 		       "%s\n", snpdev, efi_strerror ( efirc ) );
 			&efi_nii_protocol_guid, &snpdev->nii,
 			&efi_nii31_protocol_guid, &snpdev->nii,
 			&efi_component_name2_protocol_guid, &snpdev->name2,
+			&efi_load_file_protocol_guid, &snpdev->load_file,
 			NULL );
  err_install_protocol_interface:
 	bs->CloseEvent ( snpdev->snp.WaitForPacket );
 			&efi_nii_protocol_guid, &snpdev->nii,
 			&efi_nii31_protocol_guid, &snpdev->nii,
 			&efi_component_name2_protocol_guid, &snpdev->name2,
+			&efi_load_file_protocol_guid, &snpdev->load_file,
 			NULL );
 	bs->CloseEvent ( snpdev->snp.WaitForPacket );
 	netdev_put ( snpdev->netdev );