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    A Serexp & FGL Production..................................................

Cross-platform NVRAM (UEFI) variable access library.

===================================================================
						THE WHAT
===================================================================

nvwrite is a lightweight utility to read, write, and delete NVRAM variables
from user space.

- Primary target: Linux (via sysfs efivars)
- Secondary: Windows (via GetFirmwareEnvironmentVariable)

It is designed for low-level system tools and embedded-like
environments where full CRT may not be available. On Linux, it only relies
on these functions:
    close, closedir, open, opendir, read, readdir, unlink, write
These can eventually be swapped for their syscalls equivalent, but it
was not done. On Windows, we rely on {Set/Get}FirmwareEnvironmentVariable.

===================================================================
						THE HOW
===================================================================

- Minimal, self-contained C API
- Symmetric error codes across platforms
- Optional debug logging (enabled with debug builds)
- Supports reading/writing raw binary UEFI variable data

===================================================================
						THE WHAT. AGAIN.
===================================================================
---
	/* nvwrite.h */
	#define nvwrite_OK                    0
	#define nvwrite_ERR_INVALID          -1
	#define nvwrite_ERR_NOTFOUND         -2
	#define nvwrite_ERR_ACCESS           -3
	#define nvwrite_ERR_BUFFER           -4
	#define nvwrite_ERR_PLATFORM         -5

	int nvwrite_read(const char *name, void *buffer, uint32_t *size);
	int nvwrite_write(const char *name, const void *data, uint32_t size);
	int nvwrite_delete(const char *name);
	int nvwrite_list(void (*callback)(const char *name, void *ctx), void *ctx);
---

nvwrite_read: Read an NVRAM variable into buffer. On input, *size = buffer capacity;
    on output, *size = bytes read.
nvwrite_write: Write data (size bytes) to an NVRAM variable.
nvwrite_delete: Delete the specified variable.
nvwrite_list: Enumerate all variable names (Linux only; Windows returns
    nvwrite_ERR_PLATFORM). Calls callback(name, ctx) for each.

All functions return 0 (nvwrite_OK) on success, or a negative error code.

===================================================================
	Platform=specific stuff aka why we can't have nice things
===================================================================
---
	Linux

    Uses /sys/firmware/efi/efivars (requires efivarfs mounted, usually done by
        systemd or kernel).

    Requires root privileges (or CAP_SYS_ADMIN) for write/delete.

    Variable names appear as "VariableName-GUID". You must pass the full name as
        shown in the filesystem.

---
	Windows

    Uses {Set/Get}FirmwareEnvironmentVariableA.

    The GUID is hard‑coded to {00000000-0000-0000-0000-000000000000}
        (EFI_GLOBAL_VARIABLE namespace per the UEFI spec).
    For vendor‑specific variables, you would need to extend the API.

    Write/delete requires SeSystemEnvironmentPrivilege, not available to
        normal users by default.

    nvwrite_list is not implemented on Windows. For now!

===================================================================
						BUILDING
===================================================================

Release (freestanding, no libc)
	make
The object file can be linked into your project without standard libraries.

Debug (with libc, printf logging)
	make debug

===================================================================
						HOW 2 USE
===================================================================
    Check the cli.c code.

    Error Codes
nvwrite_OK (0): Success
nvwrite_ERR_INVALID: Null pointer or zero size
nvwrite_ERR_NOTFOUND: Variable does not exist
nvwrite_ERR_ACCESS: Permission denied, or kernel/OS error
nvwrite_ERR_BUFFER: Output path buffer too small (Linux only)
nvwrite_ERR_PLATFORM: Operation not supported on this OS (e.g., list on Windows)

===================================================================
						ENGINEERING NOTES
===================================================================

    Freestanding:
    In release builds (NDEBUG defined), no standard library functions are used.
    This is to support other (FGL and non-FGL) projects where using libc just isn't possible.

    Attributes:
    Linux writes the standard EFI variable attributes 0x07 (Non‑volatile + BootService
        + Runtime). Windows uses the default attributes from SetFirmwareEnvironmentVariable.

    Endianness: The Linux code assumes little‑endian for the attributes header
        (the common case for x86/ARM). For big‑endian platforms, add le32toh/htole32
            conversions.

    Security: Variable names are NOT validated for path components (.., /). This is
        deliberate. It is caller's responsibility to do so.

    Windows enumeration: Not provided due to lack of a stable public API. Soon though...!


===================================================================
                        CREDITS
===================================================================

    Serexp @ Futuristic Gadgets Laboratory.

    Words from the author:
    Another FGL classic. Only thing I did wrong was not writing it sooner.

    Come say hi, contact @ https://serexp.lain.la


===================================================================
                        License
===================================================================
    Check license.txt