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static as_area_t *find_area_and_lock(as_t *, uintptr_t);

#ifdef CONFIG_UDEBUG

/** Write directly into a page, bypassing area flags.

 *

 * This allows a debugger to write into a page that is mapped read-only

 * (such as the text segment). Naturally, this can only be done if the

 * correspoinding area is private (not shared) and anonymous.

 *

 * If this is not the case, this function calls as_area_make_writeable()

 * first.

 */

static int debug_write_inside_page(uintptr_t va, void *data, size_t n)

{

    uintptr_t page;

    pte_t *pte;

    as_area_t *area;

    uintptr_t frame;

    ipl_t ipl;

    int rc;

    page = ALIGN_DOWN(va, PAGE_SIZE);

    ASSERT(ALIGN_DOWN(va + n - 1, PAGE_SIZE) == page);

restart:

    mutex_lock(&AS->lock);

    ipl = interrupts_disable();

    area = find_area_and_lock(AS, page);

    if (area->backend != &anon_backend || area->sh_info != NULL) {

        mutex_unlock(&area->lock);

        mutex_unlock(&AS->lock);

        interrupts_restore(ipl);

        rc = as_area_make_writeable(area->base);

        if (rc != 0) return rc;

        goto restart;

    }

    pte = page_mapping_find(AS, page);

    if (! (pte && PTE_VALID(pte) && PTE_PRESENT(pte)) ) {

        mutex_unlock(&area->lock);

        mutex_unlock(&AS->lock);

        interrupts_restore(ipl);

        rc = as_page_fault(page, PF_ACCESS_WRITE, NULL);

        if (rc == AS_PF_FAULT) return EINVAL;

        goto restart;

    }

    frame = PTE_GET_FRAME(pte);

    memcpy((void *)(PA2KA(frame) + (va - page)), data, n);

    mutex_unlock(&area->lock);

    mutex_unlock(&AS->lock);

    interrupts_restore(ipl);

    return EOK;

}

/** Write data bypassing area flags.

 *

 * See debug_write_inside_page().

 */

int as_debug_write(uintptr_t va, void *data, size_t n)

{

    size_t now;

    int rc;

    while (n > 0) {

        /* Number of bytes until the end of page */

        now = ALIGN_DOWN(va, PAGE_SIZE) + PAGE_SIZE - va;

        if (now > n) now = n;

        rc = debug_write_inside_page(va, data, now);

        if (rc != EOK) return rc;

        va += now;

        data += now;

        n -= now;

    }

    return EOK;

}

/** Make sure area is private and anonymous.

 *

 * Not atomic atm.

 * @param address   Virtual address in AS.

 */

int as_area_make_writeable(uintptr_t address)

{

    ipl_t ipl;

    as_area_t *area;

    uintptr_t base, page;

    uintptr_t old_frame, frame;

    size_t size;

    int flags;

    int page_flags;

    pte_t *pte;

    int rc;

    uintptr_t *pagemap;

    ipl = interrupts_disable();

    mutex_lock(&AS->lock);

    area = find_area_and_lock(AS, address);

    if (!area) {

        /*

         * Could not find the address space area.

         */

        mutex_unlock(&AS->lock);

        interrupts_restore(ipl);

        return ENOENT;

    }

    if (area->backend == &anon_backend && !area->sh_info) {

        /* Nothing to do */

        mutex_unlock(&area->lock);

        mutex_unlock(&AS->lock);

        interrupts_restore(ipl);

        return EOK;

    }

    base = area->base;

    size = area->pages * PAGE_SIZE;

    flags = area->flags;

    page_flags = as_area_get_flags(area);

    pagemap = malloc(area->pages * sizeof(uintptr_t), 0);

    page_table_lock(AS, false);

    for (page = base; page < base + size; page += PAGE_SIZE) {

        pte = page_mapping_find(AS, page);

        if (!pte || !PTE_PRESENT(pte) || !PTE_READABLE(pte)) {

            /* Fetch the missing page */

            if (!area->backend || !area->backend->page_fault) {

                page_table_unlock(AS, false);

                mutex_unlock(&area->lock);

                mutex_unlock(&AS->lock);

                interrupts_restore(ipl);

                return EINVAL;

            }

            if (area->backend->page_fault(area, page, PF_ACCESS_READ) != AS_PF_OK) {

                page_table_unlock(AS, false);

                mutex_unlock(&area->lock);

                mutex_unlock(&AS->lock);

                interrupts_restore(ipl);

                return EINVAL;

            }

        }

        ASSERT(PTE_VALID(pte));

        old_frame = PTE_GET_FRAME(pte);

        frame = (uintptr_t)frame_alloc(ONE_FRAME, 0);

        memcpy((void *) PA2KA(frame), (void *)PA2KA(old_frame),

            FRAME_SIZE);

        pagemap[(page - base) / PAGE_SIZE] = frame;

    }

    page_table_unlock(AS, false);

    mutex_unlock(&area->lock);

    mutex_unlock(&AS->lock);

    interrupts_restore(ipl);

    rc = as_area_destroy(AS, address);

    if (rc < 0) {

        free(pagemap);

        return rc;

    }

    area = as_area_create(AS, flags, size, base, AS_AREA_ATTR_PARTIAL,

        &anon_backend, NULL);

    if (area == NULL) {

        free(pagemap);

        return rc;

    }

    mutex_lock(&AS->lock);

    mutex_lock(&area->lock);

    page_table_lock(AS, false);

    for (page = base; page < base + size; page += PAGE_SIZE) {

        frame = pagemap[(page - base) / PAGE_SIZE];

        page_mapping_insert(AS, page, frame, page_flags);

        if (!used_space_insert(area, page, 1))

            panic("Could not insert used space.\n");

    }

    page_table_unlock(AS, false);

    area->attributes &= ~AS_AREA_ATTR_PARTIAL;

    mutex_unlock(&area->lock);

    mutex_unlock(&AS->lock);

    free(pagemap);

    return EOK;

}

#endif /* defined(CONFIG_UDEBUG) */