nt-lite/code/kernel/ke_system_root.c

// System root volume selection. This file keeps boot-volume identity in one place so loaders do not guess.

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <kernel/ke_system_root.h>
#include <kernel/ke_debug.h>
#include <kernel/io_file.h>

static uint8_t gSystemRootDrive;
static bool gSystemRootReady;

// Builds a drive-qualified path without depending on any process CWD.
static bool KiBuildDrivePath(uint8_t drive, const char* relative, char* out, size_t outSize) {
    if (!relative || !out || drive >= KE_SYSTEM_ROOT_MAX_DRIVES)
        return false;

    size_t relLen = strlen(relative);
    if (relLen + 4 > outSize)
        return false;

    out[0] = (char)('0' + drive);
    out[1] = ':';
    out[2] = '/';
    memcpy(out + 3, relative, relLen + 1);
    return true;
}

// Returns true when the candidate volume looks like the volume that booted the kernel.
static bool KiDriveLooksLikeSystemRoot(uint8_t drive) {
    static const char* required[] = {
        "system/colonel.exe",
        "system/hal.dll",
        "drivers/drivers.ini",
    };

    char path[1024];
    for (size_t i = 0; i < sizeof(required) / sizeof(required[0]); i++) {
        if (!KiBuildDrivePath(drive, required[i], path, sizeof(path)))
            return false;

        FILE_OBJECT* file = NULL;
        KSTATUS s = IoOpenFile(SysSvFromCstr(path), &file);
        if (!KSUCCESS(s))
            return false;
        IoCloseFile(file);
    }

    return true;
}

// Selects the mounted volume that contains the kernel/system tree.
KSTATUS KeInitializeSystemRootVolume(void) {
    for (uint8_t drive = 0; drive < KE_SYSTEM_ROOT_MAX_DRIVES; drive++) {
        if (!IoFilesystemPresent(drive))
            continue;
        if (!KiDriveLooksLikeSystemRoot(drive))
            continue;

        gSystemRootDrive = drive;
        gSystemRootReady = true;
        DbgPrint("System root: drive=%u\n", drive);
        return STATUS_SUCCESS;
    }

    return STATUS_NOT_FOUND;
}

// Returns whether the system root volume has been selected.
bool KeSystemRootReady(void) {
    return gSystemRootReady;
}

// Returns the selected system root drive, or zero before discovery.
uint8_t KeGetSystemRootDrive(void) {
    return gSystemRootReady ? gSystemRootDrive : 0;
}

// Builds an absolute path rooted at the selected system volume.
bool KeBuildSystemRootPath(const char* relative, char* out, size_t outSize) {
    if (!gSystemRootReady)
        return false;
    return KiBuildDrivePath(gSystemRootDrive, relative, out, outSize);
}

// Opens a file rooted at the selected system volume.
KSTATUS KeOpenSystemRootFile(const char* relative, FILE_OBJECT** out) {
    if (!out)
        return STATUS_INVALID_PARAMETER;
    *out = NULL;

    char path[1024];
    if (!KeBuildSystemRootPath(relative, path, sizeof(path)))
        return STATUS_NOT_FOUND;
    return IoOpenFile(SysSvFromCstr(path), out);
}