How can I get input in POSIX-UEFI?

Question

I want to make a DOS-inspired UEFI operating system, simple, a good place to start. Take in commands and run those commands, but I don't quite get the "Take in commands" part. In POSIX-UEFI, uefi.h has a custom printf, so I'm assuming it needs a custom scanf, given a different I/O system (educated guess).

I've tried quite a few things. I blatantly tried putting scanf in my code, and I got an implicit function declaration warning, so no scanf in uefi.h, it appears. I searched up loads of things and I didn't get anything back that was relevant to my problem, so I have came here.

Thanks in advance :).

Answer 1

From the looks of things, you end up using uefi services (fairly) directly. During startup, it initializes a global variable named ST to point to the UEFI system table, which looks like this (uefi.h, line 846):

typedef struct {
    efi_table_header_t              Hdr;

    wchar_t                         *FirmwareVendor;
    uint32_t                        FirmwareRevision;

    efi_handle_t                    ConsoleInHandle;
    simple_input_interface_t        *ConIn;

    efi_handle_t                    ConsoleOutHandle;
    simple_text_output_interface_t  *ConOut;

    efi_handle_t                    ConsoleErrorHandle;
    simple_text_output_interface_t  *StdErr;

    efi_runtime_services_t          *RuntimeServices;
    efi_boot_services_t             *BootServices;

    uintn_t                         NumberOfTableEntries;
    efi_configuration_table_t       *ConfigurationTable;
} efi_system_table_t;

To read from the keyboard, you'll use the ConIn, which is a pointer to a simple_input_interface_t, which is defined as follows (uefi.h, line 576):

typedef struct {
    efi_input_reset_t           Reset;
    efi_input_read_key_t        ReadKeyStroke;
    efi_event_t                 WaitForKey;
} simple_input_interface_t;

At a guess, you'll probably want to allocate a buffer of reasonable size. Then use WaitForKey/ReadKeyStroke to read keys and save them to the buffer until you get a carriage return.

Then you can use something like sscanf to parse the content of the buffer.

Reference

uefi.h

Answer 2

In POSIX-UEFI, handling user input can differ due to its I/O system. As scanf isn't explicitly supported in uefi.h, you'll likely need to implement a custom input function for your DOS-inspired OS. Consider exploring alternatives like parsing input buffers or creating a custom input handler using available UEFI functionalities to achieve command intake.