/*
 *      linux/mm/mincore.c
 *
 * Copyright (C) 1994-1999  Linus Torvalds
 */

/*
 * The mincore() system call.
 */
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/syscalls.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>

/*
 * Later we can get more picky about what "in core" means precisely.
 * For now, simply check to see if the page is in the page cache,
 * and is up to date; i.e. that no page-in operation would be required
 * at this time if an application were to map and access this page.
 */
static unsigned char mincore_page(struct vm_area_struct * vma,
        unsigned long pgoff)
{
        unsigned char present = 0;
        struct address_space * as = vma->vm_file->f_mapping;
        struct page * page;

        page = find_get_page(as, pgoff);
        if (page) {
                present = PageUptodate(page);
                page_cache_release(page);
        }

        return present;
}

static long mincore_vma(struct vm_area_struct * vma,
        unsigned long start, unsigned long end, unsigned char __user * vec)
{
        long error, i, remaining;
        unsigned char * tmp;

        error = -ENOMEM;
        if (!vma->vm_file)
                return error;

        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;

        error = -EAGAIN;
        tmp = (unsigned char *) __get_free_page(GFP_KERNEL);
        if (!tmp)
                return error;

        /* (end - start) is # of pages, and also # of bytes in "vec */
        remaining = (end - start),

        error = 0;
        for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) {
                int j = 0;
                long thispiece = (remaining < PAGE_SIZE) ?
                                                remaining : PAGE_SIZE;

                while (j < thispiece)
                        tmp[j++] = mincore_page(vma, start++);

                if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) {
                        error = -EFAULT;
                        break;
                }
        }

        free_page((unsigned long) tmp);
        return error;
}

/*
 * The mincore(2) system call.
 *
 * mincore() returns the memory residency status of the pages in the
 * current process's address space specified by [addr, addr + len).
 * The status is returned in a vector of bytes.  The least significant
 * bit of each byte is 1 if the referenced page is in memory, otherwise
 * it is zero.
 *
 * Because the status of a page can change after mincore() checks it
 * but before it returns to the application, the returned vector may
 * contain stale information.  Only locked pages are guaranteed to
 * remain in memory.
 *
 * return values:
 *  zero    - success
 *  -EFAULT - vec points to an illegal address
 *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE,
 *              or len has a nonpositive value
 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 *              invalid for the address space of this process, or
 *              specify one or more pages which are not currently
 *              mapped
 *  -EAGAIN - A kernel resource was temporarily unavailable.
 */
asmlinkage long sys_mincore(unsigned long start, size_t len,
        unsigned char __user * vec)
{
        int index = 0;
        unsigned long end, limit;
        struct vm_area_struct * vma;
        size_t max;
        int unmapped_error = 0;
        long error;

        /* check the arguments */
        if (start & ~PAGE_CACHE_MASK)
                goto einval;

        if (start < FIRST_USER_PGD_NR * PGDIR_SIZE)
                goto enomem;

        limit = TASK_SIZE;
        if (start >= limit)
                goto enomem;

        max = limit - start;
        len = PAGE_CACHE_ALIGN(len);
        if (len > max)
                goto einval;

        end = start + len;

        /* check the output buffer whilst holding the lock */
        error = -EFAULT;
        down_read(&current->mm->mmap_sem);

        if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
                goto out;

        /*
         * If the interval [start,end) covers some unmapped address
         * ranges, just ignore them, but return -ENOMEM at the end.
         */
        error = 0;

        vma = find_vma(current->mm, start);
        while (vma) {
                /* 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 = mincore_vma(vma, start, end,
                                                        &vec[index]);
                                if (error)
                                        goto out;
                        }
                        error = unmapped_error;
                        goto out;
                }

                /* Here vma->vm_start <= start < vma->vm_end < end. */
                error = mincore_vma(vma, start, vma->vm_end, &vec[index]);
                if (error)
                        goto out;
                index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT;
                start = vma->vm_end;
                vma = vma->vm_next;
        }

        /* we found a hole in the area queried if we arrive here */
        error = -ENOMEM;

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

einval:
        return -EINVAL;
enomem:
        return -ENOMEM;
}