#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
#include <linux/sched.h>

/**
 * get_vaddr_frames() - map virtual addresses to pfns
 * @start:      starting user address
 * @nr_frames:  number of pages / pfns from start to map
 * @write:      whether pages will be written to by the caller
 * @force:      whether to force write access even if user mapping is
 *              readonly. See description of the same argument of
                get_user_pages().
 * @vec:        structure which receives pages / pfns of the addresses mapped.
 *              It should have space for at least nr_frames entries.
 *
 * This function maps virtual addresses from @start and fills @vec structure
 * with page frame numbers or page pointers to corresponding pages (choice
 * depends on the type of the vma underlying the virtual address). If @start
 * belongs to a normal vma, the function grabs reference to each of the pages
 * to pin them in memory. If @start belongs to VM_IO | VM_PFNMAP vma, we don't
 * touch page structures and the caller must make sure pfns aren't reused for
 * anything else while he is using them.
 *
 * The function returns number of pages mapped which may be less than
 * @nr_frames. In particular we stop mapping if there are more vmas of
 * different type underlying the specified range of virtual addresses.
 * When the function isn't able to map a single page, it returns error.
 *
 * This function takes care of grabbing mmap_sem as necessary.
 */
int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
                     bool write, bool force, struct frame_vector *vec)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        int ret = 0;
        int err;
        int locked;

        if (nr_frames == 0)
                return 0;

        if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
                nr_frames = vec->nr_allocated;

        down_read(&mm->mmap_sem);
        locked = 1;
        vma = find_vma_intersection(mm, start, start + 1);
        if (!vma) {
                ret = -EFAULT;
                goto out;
        }
        if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
                vec->got_ref = true;
                vec->is_pfns = false;
                ret = get_user_pages_locked(start, nr_frames,
                        write, force, (struct page **)(vec->ptrs), &locked);
                goto out;
        }

        vec->got_ref = false;
        vec->is_pfns = true;
        do {
                unsigned long *nums = frame_vector_pfns(vec);

                while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
                        err = follow_pfn(vma, start, &nums[ret]);
                        if (err) {
                                if (ret == 0)
                                        ret = err;
                                goto out;
                        }
                        start += PAGE_SIZE;
                        ret++;
                }
                /*
                 * We stop if we have enough pages or if VMA doesn't completely
                 * cover the tail page.
                 */
                if (ret >= nr_frames || start < vma->vm_end)
                        break;
                vma = find_vma_intersection(mm, start, start + 1);
        } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
out:
        if (locked)
                up_read(&mm->mmap_sem);
        if (!ret)
                ret = -EFAULT;
        if (ret > 0)
                vec->nr_frames = ret;
        return ret;
}
EXPORT_SYMBOL(get_vaddr_frames);

/**
 * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 *                      them
 * @vec:        frame vector to put
 *
 * Drop references to pages if get_vaddr_frames() acquired them. We also
 * invalidate the frame vector so that it is prepared for the next call into
 * get_vaddr_frames().
 */
void put_vaddr_frames(struct frame_vector *vec)
{
        int i;
        struct page **pages;

        if (!vec->got_ref)
                goto out;
        pages = frame_vector_pages(vec);
        /*
         * frame_vector_pages() might needed to do a conversion when
         * get_vaddr_frames() got pages but vec was later converted to pfns.
         * But it shouldn't really fail to convert pfns back...
         */
        if (WARN_ON(IS_ERR(pages)))
                goto out;
        for (i = 0; i < vec->nr_frames; i++)
                put_page(pages[i]);
        vec->got_ref = false;
out:
        vec->nr_frames = 0;
}
EXPORT_SYMBOL(put_vaddr_frames);

/**
 * frame_vector_to_pages - convert frame vector to contain page pointers
 * @vec:        frame vector to convert
 *
 * Convert @vec to contain array of page pointers.  If the conversion is
 * successful, return 0. Otherwise return an error. Note that we do not grab
 * page references for the page structures.
 */
int frame_vector_to_pages(struct frame_vector *vec)
{
        int i;
        unsigned long *nums;
        struct page **pages;

        if (!vec->is_pfns)
                return 0;
        nums = frame_vector_pfns(vec);
        for (i = 0; i < vec->nr_frames; i++)
                if (!pfn_valid(nums[i]))
                        return -EINVAL;
        pages = (struct page **)nums;
        for (i = 0; i < vec->nr_frames; i++)
                pages[i] = pfn_to_page(nums[i]);
        vec->is_pfns = false;
        return 0;
}
EXPORT_SYMBOL(frame_vector_to_pages);

/**
 * frame_vector_to_pfns - convert frame vector to contain pfns
 * @vec:        frame vector to convert
 *
 * Convert @vec to contain array of pfns.
 */
void frame_vector_to_pfns(struct frame_vector *vec)
{
        int i;
        unsigned long *nums;
        struct page **pages;

        if (vec->is_pfns)
                return;
        pages = (struct page **)(vec->ptrs);
        nums = (unsigned long *)pages;
        for (i = 0; i < vec->nr_frames; i++)
                nums[i] = page_to_pfn(pages[i]);
        vec->is_pfns = true;
}
EXPORT_SYMBOL(frame_vector_to_pfns);

/**
 * frame_vector_create() - allocate & initialize structure for pinned pfns
 * @nr_frames:  number of pfns slots we should reserve
 *
 * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
 * pfns.
 */
struct frame_vector *frame_vector_create(unsigned int nr_frames)
{
        struct frame_vector *vec;
        int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;

        if (WARN_ON_ONCE(nr_frames == 0))
                return NULL;
        /*
         * This is absurdly high. It's here just to avoid strange effects when
         * arithmetics overflows.
         */
        if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
                return NULL;
        /*
         * Avoid higher order allocations, use vmalloc instead. It should
         * be rare anyway.
         */
        if (size <= PAGE_SIZE)
                vec = kmalloc(size, GFP_KERNEL);
        else
                vec = vmalloc(size);
        if (!vec)
                return NULL;
        vec->nr_allocated = nr_frames;
        vec->nr_frames = 0;
        return vec;
}
EXPORT_SYMBOL(frame_vector_create);

/**
 * frame_vector_destroy() - free memory allocated to carry frame vector
 * @vec:        Frame vector to free
 *
 * Free structure allocated by frame_vector_create() to carry frames.
 */
void frame_vector_destroy(struct frame_vector *vec)
{
        /* Make sure put_vaddr_frames() got called properly... */
        VM_BUG_ON(vec->nr_frames > 0);
        kvfree(vec);
}
EXPORT_SYMBOL(frame_vector_destroy);