Move lessons to separate folder

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>

1 files changed, 0 insertions, 359 deletions

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-Let's print content of variables that define boot options in UEFI.
-
-To do it, we need to use `GetVariable()` API function from the EFI Runtime Services:
-```
-GetVariable()
-
-Summary:
-Returns the value of a variable.
-
-Prototype:
-typedef
-EFI_STATUS
-GetVariable (
- IN CHAR16 *VariableName,
- IN EFI_GUID *VendorGuid,
- OUT UINT32 *Attributes OPTIONAL,
- IN OUT UINTN *DataSize,
- OUT VOID *Data OPTIONAL
- );
-
-Parameters:
-VariableName    A Null-terminated string that is the name of the vendor’s variable.
-VendorGuid      A unique identifier for the vendor
-Attributes      If not NULL, a pointer to the memory location to return the
-                attributes bitmask for the variable.
-                If not NULL, then Attributes is set on output both when
-                EFI_SUCCESS and when EFI_BUFFER_TOO_SMALL is returned.
-DataSize        On input, the size in bytes of the return Data buffer.
-                On output the size of data returned in Data.
-Data            The buffer to return the contents of the variable. May be NULL
-                with a zero DataSize in order to determine the size buffer needed.
-
-Description:
-Each vendor may create and manage its own variables without the risk of name conflicts by using a
-unique VendorGuid. When a variable is set its Attributes are supplied to indicate how the data variable
-should be stored and maintained by the system. The attributes affect when the variable may be accessed
-and volatility of the data
-
-If the Data buffer is too small to hold the contents of the variable, the error EFI_BUFFER_TOO_SMALL is
-returned and DataSize is set to the required buffer size to obtain the data.
-
-Status Codes Returned:
-EFI_SUCCESS 		The function completed successfully.
-EFI_NOT_FOUND 		The variable was not found.
-EFI_BUFFER_TOO_SMALL 	The DataSize is too small for the result. DataSize has been
-			updated with the size needed to complete the request. If
-			Attributes is not NULL, then the attributes bitmask for the
-			variable has been stored to the memory location pointed-to by
-			Attributes.
-...
-
-```
-
-In previous lesson we've discovered that these options are present in our environment under GUID `EFI_GLOBAL_VARIABLE` (gEfiGlobalVariableGuid):
-```
-Boot0000
-Boot0001
-Boot0002
-Boot0003
-Boot0004
-BootCurrent
-BootOrder
-```
-
-If we look at the UEFI spec for these options description we would find:
-```
-Each Boot#### variable contains an EFI_LOAD_OPTION. Each Boot#### variable is the name “Boot”
-appended with a unique four digit hexadecimal number. For example, Boot0001, Boot0002, Boot0A02,
-etc.
-
-...
-
-The BootOrder variable contains an array of UINT16’s that make up an ordered list of the Boot####
-options. The first element in the array is the value for the first logical boot option, the second element is
-the value for the second logical boot option, etc. The BootOrder order list is used by the firmware’s
-boot manager as the default boot order.
-
-...
-
-The BootCurrent variable is a single UINT16 that defines the Boot#### option that was selected on
-the current boot.
-```
-
-Create `ShowBootVariables` for this lesson.
-
-First let's try to get simple `UINT16 BootCurrent` option.
-
-We would be getting variables a lot in this program, so it is best to create a function that abstracts all the necessities of the `GetVariable` API calls:
-```
-EFI_STATUS
-GetNvramVariable( CHAR16   *VariableName,
-                  EFI_GUID *VariableOwnerGuid,
-                  VOID     **Buffer,
-                  UINTN    *BufferSize)
-{
-    UINTN Size = 0;
-    *BufferSize = 0;
-
-    EFI_STATUS Status = gRT->GetVariable(VariableName, VariableOwnerGuid, NULL, &Size, NULL);
-    if (Status != EFI_BUFFER_TOO_SMALL) {
-        Print(L"Error! 'gRT->GetVariable' call returned %r\n", Status);
-        return Status;
-    }
-
-    *Buffer = AllocateZeroPool(Size);
-    if (!Buffer) {
-        Print(L"Error! 'AllocateZeroPool' call returned %r\n", Status);
-        return EFI_OUT_OF_RESOURCES;
-    }
-
-    Status = gRT->GetVariable(VariableName, VariableOwnerGuid, NULL, &Size, *Buffer);
-    if (Status == EFI_SUCCESS) {
-        *BufferSize = Size;
-    } else {
-        FreePool( *Buffer );
-        *Buffer = NULL;
-    }
-
-    return Status;
-}
-```
-
-As with many other different UEFI APIs first `GetVariable` call gives us `EFI_BUFFER_TOO_SMALL` error, but fills `Size` variable with the size of the array that we need to allocate and pass to this function for the correct execution.
-We allocate necessary size with the `AllocateZeroPool` edk2 library call, like we did it in previous lesson. After that we call `GetVariable` function for the second time, expecting `EFI_SUCCESS` status.
-
-
-The main function would look like this:
-```
-#include <Library/UefiRuntimeServicesTableLib.h>
-#include <Library/UefiBootServicesTableLib.h>
-#include <Library/UefiLib.h>
-#include <Library/MemoryAllocationLib.h>
-
-EFI_STATUS
-GetNvramVariable( CHAR16   *VariableName,
-                  EFI_GUID *VariableOwnerGuid,
-                  VOID     **Buffer,
-                  UINTN    *BufferSize)
-{
-  ...
-}
-
-INTN EFIAPI ShellAppMain(IN UINTN Argc, IN CHAR16 **Argv)
-{
-  UINTN OptionSize;
-  EFI_STATUS Status;
-
-  UINT16* BootCurrent;
-  Status = GetNvramVariable(L"BootCurrent", &gEfiGlobalVariableGuid, (VOID**)&BootCurrent, &OptionSize);
-  if (Status == EFI_SUCCESS) {
-    Print(L"BootCurrent=%d\n", *BootCurrent);
-  } else {
-    Print(L"Can't get BootCurrent variable\n");
-  }
-
-  return EFI_SUCCESS;
-}
-```
-
-If we execute this code under OVMF we would get:
-```
-FS0:\> ShowBootVariables.efi
-3
-```
-This means that `Boot0003` is active.
-
-
-Now let's get `UINT16 BootOrder[]` variable. It is an array of XXXX numbers that describe Boot option priority.
-So `{0,2,4,1,3}` for example would mean this order:
-```
-Boot0000
-Boot0002
-Boot0004
-Boot0001
-Boot0003
-```
-
-This is the code to get and print this array:
-```
-UINT16* BootOrderArray;
-Status = GetNvramVariable(L"BootOrder", &gEfiGlobalVariableGuid, (VOID**)&BootOrderArray, &OptionSize);
-if (Status == EFI_SUCCESS) {
-  for (UINTN i=0; i<(OptionSize/sizeof(UINT16)); i++) {
-    Print(L"Boot%04d%s\n", BootOrderArray[i], (BootOrderArray[i] == *BootCurrent)? L"*" : L"" );
-  }
-} else {
-  Print(L"Can't get BootOrder variable\n");
-}
-```
-
-If we execute this code under OVMF we would get:
-```
-Boot0000
-Boot0001
-Boot0002
-Boot0003*
-Boot0004
-```
-
-
-Now let's print information about every `Boot####` option.
-
-According to the UEFI the spec these options are stored in a `EFI_LOAD_OPTION` structure:
-```
-typedef struct _EFI_LOAD_OPTION {
- UINT32 Attributes;
- UINT16 FilePathListLength;
- // CHAR16 Description[];
- // EFI_DEVICE_PATH_PROTOCOL FilePathList[];
- // UINT8 OptionalData[];
-} EFI_LOAD_OPTION;
-
-Parameters
-Attributes 		The attributes for this load option entry. All unused bits must be zero
-			and are reserved by the UEFI specification for future growth.
-FilePathListLength	Length in bytes of the FilePathList. OptionalData starts at
-			offset sizeof(UINT32) + sizeof(UINT16) +
-			StrSize(Description) + FilePathListLength of the
-			EFI_LOAD_OPTION descriptor.
-Description 		The user readable description for the load option. This field ends
-			with a Null character.
-FilePathList 		A packed array of UEFI device paths. The first element of the array is
-			a device path that describes the device and location of the Image for
-			this load option. The FilePathList[0] is specific to the device
-			type. Other device paths may optionally exist in the FilePathList,
-			but their usage is OSV specific. Each element in the array is variable
-			length, and ends at the device path end structure. Because the size
-			of Description is arbitrary, this data structure is not guaranteed
-			to be aligned on a natural boundary. This data structure may have to
-			be copied to an aligned natural boundary before it is used.
-OptionalData 		The remaining bytes in the load option descriptor are a binary data
-			buffer that is passed to the loaded image. If the field is zero bytes
-			long, a NULL pointer is passed to the loaded image. The number of
-			bytes in OptionalData can be computed by subtracting the
-			starting offset of OptionalData from total size in bytes of the
-			EFI_LOAD_OPTION. 
-```
-In edk2 it is defined in a file https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Uefi/UefiSpec.h
-
-Pay attention to the fact that some fields in this structure are commented:
-```
-// CHAR16 Description[];
-// EFI_DEVICE_PATH_PROTOCOL FilePathList[];
-// UINT8 OptionalData[];
-```
-It is because these fields are variable size arrays, so we need to calculate offsets to them dynamically.
-
-Create a function that accepts names of a Boot variable (such as "Boot0003") and outputs all the needed information about it:
-```
-VOID PrintBootOption(CHAR16* BootOptionName)
-{
-  UINTN OptionSize;
-  UINT8* Buffer;
-
-  EFI_STATUS Status = GetNvramVariable(BootOptionName, &gEfiGlobalVariableGuid, (VOID**)&Buffer, &OptionSize);
-  if (Status == EFI_SUCCESS) {
-      EFI_LOAD_OPTION* LoadOption = (EFI_LOAD_OPTION*) Buffer;
-      CHAR16* Description = (CHAR16*)(Buffer + sizeof (EFI_LOAD_OPTION));
-      UINTN DescriptionSize = StrSize(Description);
-
-      Print(L"%s\n", Description);
-      if (LoadOption->FilePathListLength != 0) {
-        VOID* FilePathList = (UINT8 *)Description + DescriptionSize;
-        CHAR16* DevPathString = ConvertDevicePathToText(FilePathList, TRUE, FALSE);
-        Print(L"%s\n", DevPathString);
-      }
-  } else {
-    Print(L"Can't get %s variable\n", BootOptionName);
-  }
-}
-```
-
-This code uses pointer arithmetics that we've discussed above. To get `Description` field size we simply use `StrSize(Description)` call as `Description` field always ends with Null.
-
-To print DevicePath as a string we use `ConvertDevicePathToText` call (we've used it earlier in our `ImageInfo` application). To use it we need to add `#include <Library/DevicePathLib.h>` to our program.
-
-Now we need to construct "BootXXXX" variables from a `BootOrder` numbers.
-
-To do so we would use `UnicodeSPrint` function from the https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Library/PrintLib.h
-```
-/**
-  Produces a Null-terminated Unicode string in an output buffer based on a Null-terminated
-  Unicode format string and variable argument list.
-  This function is similar as snprintf_s defined in C11.
-
-  ...
-
-  @param  StartOfBuffer   A pointer to the output buffer for the produced Null-terminated
-                          Unicode string.
-  @param  BufferSize      The size, in bytes, of the output buffer specified by StartOfBuffer.
-  @param  FormatString    A Null-terminated Unicode format string.
-  @param  ...             Variable argument list whose contents are accessed based on the
-                          format string specified by FormatString.
-  @return The number of Unicode characters in the produced output buffer not including the
-          Null-terminator.
-**/
-
-UINTN
-EFIAPI
-UnicodeSPrint (
-  OUT CHAR16        *StartOfBuffer,
-  IN  UINTN         BufferSize,
-  IN  CONST CHAR16  *FormatString,
-  ...
-  );
-```
-
-Just in case in the same file there is a similar function for ASCII:
-```
-UINTN
-EFIAPI
-AsciiSPrint (
-  OUT CHAR8        *StartOfBuffer,
-  IN  UINTN        BufferSize,
-  IN  CONST CHAR8  *FormatString,
-  ...
-  );
-```
-
-
-So the code inside BootOrder loop now would look like this:
-```
-CHAR16 BootOptionStr[sizeof("Boot####")+1];
-UnicodeSPrint(BootOptionStr, (sizeof("Boot####")+1)*sizeof(CHAR16), L"Boot%04x", BootOrderArray[i]);
-Print(L"%s%s\n", BootOptionStr, (BootOrderArray[i] == *BootCurrent)? L"*" : L"" );
-PrintBootOption(BootOptionStr);
-Print(L"\n");
-```
-
-Don't forget to add `#include <Library/PrintLib.h>` to the start of the file.
-
-
-If we compile our app and execute it under OVMF we would get:
-```
-FS0:\> ShowBootVariables.efi
-Boot0000
-UiApp
-Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331)
-
-Boot0001
-UEFI QEMU DVD-ROM QM00003
-PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)
-
-Boot0002
-UEFI QEMU HARDDISK QM00001
-PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)
-
-Boot0003*
-EFI Internal Shell
-Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(7C04A583-9E3E-4F1C-AD65-E05268D0B4D1)
-
-Boot0004
-UEFI PXEv4 (MAC:525400123456)
-PciRoot(0x0)/Pci(0x3,0x0)/MAC(525400123456,0x1)/IPv4(0.0.0.0)
-```
-
-We are definitely in the UEFI shell, so the `BootCurrent`(="*") is placed correctly.
-
-