/*
 *      linux/mm/madvise.c
 *
 * Copyright (C) 1999  Linus Torvalds
 * Copyright (C) 2002  Christoph Hellwig
 */

#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>

/*
 * We can potentially split a vm area into separate
 * areas, each area with its own behavior.
 */
static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
                             unsigned long end, int behavior)
{
        struct mm_struct * mm = vma->vm_mm;
        int error = 0;

        if (start != vma->vm_start) {
                error = split_vma(mm, vma, start, 1);
                if (error)
                        goto out;
        }

        if (end != vma->vm_end) {
                error = split_vma(mm, vma, end, 0);
                if (error)
                        goto out;
        }

        /*
         * vm_flags is protected by the mmap_sem held in write mode.
         */
        VM_ClearReadHint(vma);

        switch (behavior) {
        case MADV_SEQUENTIAL:
                vma->vm_flags |= VM_SEQ_READ;
                break;
        case MADV_RANDOM:
                vma->vm_flags |= VM_RAND_READ;
                break;
        default:
                break;
        }

out:
        if (error == -ENOMEM)
                error = -EAGAIN;
        return error;
}

/*
 * Schedule all required I/O operations.  Do not wait for completion.
 */
static long madvise_willneed(struct vm_area_struct * vma,
                             unsigned long start, unsigned long end)
{
        struct file *file = vma->vm_file;

        if (!file)
                return -EBADF;

        start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
        if (end > vma->vm_end)
                end = vma->vm_end;
        end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

        force_page_cache_readahead(file->f_mapping,
                        file, start, max_sane_readahead(end - start));
        return 0;
}

/*
 * Application no longer needs these pages.  If the pages are dirty,
 * it's OK to just throw them away.  The app will be more careful about
 * data it wants to keep.  Be sure to free swap resources too.  The
 * zap_page_range call sets things up for refill_inactive to actually free
 * these pages later if no one else has touched them in the meantime,
 * although we could add these pages to a global reuse list for
 * refill_inactive to pick up before reclaiming other pages.
 *
 * NB: This interface discards data rather than pushes it out to swap,
 * as some implementations do.  This has performance implications for
 * applications like large transactional databases which want to discard
 * pages in anonymous maps after committing to backing store the data
 * that was kept in them.  There is no reason to write this data out to
 * the swap area if the application is discarding it.
 *
 * An interface that causes the system to free clean pages and flush
 * dirty pages is already available as msync(MS_INVALIDATE).
 */
static long madvise_dontneed(struct vm_area_struct * vma,
                             unsigned long start, unsigned long end)
{
        if ((vma->vm_flags & VM_LOCKED) || is_vm_hugetlb_page(vma))
                return -EINVAL;

        if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
                struct zap_details details = {
                        .nonlinear_vma = vma,
                        .last_index = ULONG_MAX,
                };
                zap_page_range(vma, start, end - start, &details);
        } else
                zap_page_range(vma, start, end - start, NULL);
        return 0;
}

static long madvise_vma(struct vm_area_struct * vma, unsigned long start,
                        unsigned long end, int behavior)
{
        long error = -EBADF;

        switch (behavior) {
        case MADV_NORMAL:
        case MADV_SEQUENTIAL:
        case MADV_RANDOM:
                error = madvise_behavior(vma, start, end, behavior);
                break;

        case MADV_WILLNEED:
                error = madvise_willneed(vma, start, end);
                break;

        case MADV_DONTNEED:
                error = madvise_dontneed(vma, start, end);
                break;

        default:
                error = -EINVAL;
                break;
        }
                
        return error;
}

/*
 * The madvise(2) system call.
 *
 * Applications can use madvise() to advise the kernel how it should
 * handle paging I/O in this VM area.  The idea is to help the kernel
 * use appropriate read-ahead and caching techniques.  The information
 * provided is advisory only, and can be safely disregarded by the
 * kernel without affecting the correct operation of the application.
 *
 * behavior values:
 *  MADV_NORMAL - the default behavior is to read clusters.  This
 *              results in some read-ahead and read-behind.
 *  MADV_RANDOM - the system should read the minimum amount of data
 *              on any access, since it is unlikely that the appli-
 *              cation will need more than what it asks for.
 *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 *              once, so they can be aggressively read ahead, and
 *              can be freed soon after they are accessed.
 *  MADV_WILLNEED - the application is notifying the system to read
 *              some pages ahead.
 *  MADV_DONTNEED - the application is finished with the given range,
 *              so the kernel can free resources associated with it.
 *
 * return values:
 *  zero    - success
 *  -EINVAL - start + len < 0, start is not page-aligned,
 *              "behavior" is not a valid value, or application
 *              is attempting to release locked or shared pages.
 *  -ENOMEM - addresses in the specified range are not currently
 *              mapped, or are outside the AS of the process.
 *  -EIO    - an I/O error occurred while paging in data.
 *  -EBADF  - map exists, but area maps something that isn't a file.
 *  -EAGAIN - a kernel resource was temporarily unavailable.
 */
asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
{
        unsigned long end;
        struct vm_area_struct * vma;
        int unmapped_error = 0;
        int error = -EINVAL;
        size_t len;

        down_write(&current->mm->mmap_sem);

        if (start & ~PAGE_MASK)
                goto out;
        len = (len_in + ~PAGE_MASK) & PAGE_MASK;

        /* Check to see whether len was rounded up from small -ve to zero */
        if (len_in && !len)
                goto out;

        end = start + len;
        if (end < start)
                goto out;

        error = 0;
        if (end == start)
                goto out;

        /*
         * If the interval [start,end) covers some unmapped address
         * ranges, just ignore them, but return -ENOMEM at the end.
         */
        vma = find_vma(current->mm, start);
        for (;;) {
                /* Still start < end. */
                error = -ENOMEM;
                if (!vma)
                        goto out;

                /* Here start < vma->vm_end. */
                if (start < vma->vm_start) {
                        unmapped_error = -ENOMEM;
                        start = vma->vm_start;
                }

                /* Here vma->vm_start <= start < vma->vm_end. */
                if (end <= vma->vm_end) {
                        if (start < end) {
                                error = madvise_vma(vma, start, end,
                                                        behavior);
                                if (error)
                                        goto out;
                        }
                        error = unmapped_error;
                        goto out;
                }

                /* Here vma->vm_start <= start < vma->vm_end < end. */
                error = madvise_vma(vma, start, vma->vm_end, behavior);
                if (error)
                        goto out;
                start = vma->vm_end;
                vma = vma->vm_next;
        }

out:
        up_write(&current->mm->mmap_sem);
        return error;
}