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/*

 *      linux/mm/mincore.c

 *

 * Copyright (C) 1994-2006  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 <linux/swap.h>

#include <linux/swapops.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 address_space *mapping, pgoff_t pgoff)

{

        unsigned char present = 0;

        struct page *page;

        /*

         * When tmpfs swaps out a page from a file, any process mapping that

         * file will not get a swp_entry_t in its pte, but rather it is like

         * any other file mapping (ie. marked !present and faulted in with

         * tmpfs's .nopage). So swapped out tmpfs mappings are tested here.

         *

         * However when tmpfs moves the page from pagecache and into swapcache,

         * it is still in core, but the find_get_page below won't find it.

         * No big deal, but make a note of it.

         */

        page = find_get_page(mapping, pgoff);

        if (page) {

                present = PageUptodate(page);

                page_cache_release(page);

        }

        return present;

}

/*

 * Do a chunk of "sys_mincore()". We've already checked

 * all the arguments, we hold the mmap semaphore: we should

 * just return the amount of info we're asked for.

 */

static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)

{

        pgd_t *pgd;

        pud_t *pud;

        pmd_t *pmd;

        pte_t *ptep;

        spinlock_t *ptl;

        unsigned long nr;

        int i;

        pgoff_t pgoff;

        struct vm_area_struct *vma = find_vma(current->mm, addr);

        /*

         * find_vma() didn't find anything above us, or we're

         * in an unmapped hole in the address space: ENOMEM.

         */

        if (!vma || addr < vma->vm_start)

                return -ENOMEM;

        /*

         * Calculate how many pages there are left in the last level of the

         * PTE array for our address.

         */

        nr = PTRS_PER_PTE - ((addr >> PAGE_SHIFT) & (PTRS_PER_PTE-1));

        /*

         * Don't overrun this vma

         */

        nr = min(nr, (vma->vm_end - addr) >> PAGE_SHIFT);

        /*

         * Don't return more than the caller asked for

         */

        nr = min(nr, pages);

        pgd = pgd_offset(vma->vm_mm, addr);

        if (pgd_none_or_clear_bad(pgd))

                goto none_mapped;

        pud = pud_offset(pgd, addr);

        if (pud_none_or_clear_bad(pud))

                goto none_mapped;

        pmd = pmd_offset(pud, addr);

        if (pmd_none_or_clear_bad(pmd))

                goto none_mapped;

        ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);

        for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) {

                unsigned char present;

                pte_t pte = *ptep;

                if (pte_present(pte)) {

                        present = 1;

                } else if (pte_none(pte)) {

                        if (vma->vm_file) {

                                pgoff = linear_page_index(vma, addr);

                                present = mincore_page(vma->vm_file->f_mapping,

                                                        pgoff);

                        } else

                                present = 0;

                } else if (pte_file(pte)) {

                        pgoff = pte_to_pgoff(pte);

                        present = mincore_page(vma->vm_file->f_mapping, pgoff);

                } else { /* pte is a swap entry */

                        swp_entry_t entry = pte_to_swp_entry(pte);

                        if (is_migration_entry(entry)) {

                                /* migration entries are always uptodate */

                                present = 1;

                        } else {

#ifdef CONFIG_SWAP

                                pgoff = entry.val;

                                present = mincore_page(&swapper_space, pgoff);

#else

                                WARN_ON(1);

                                present = 1;

#endif

                        }

                }

                vec[i] = present;

        }

        pte_unmap_unlock(ptep-1, ptl);

        return nr;

none_mapped:

        if (vma->vm_file) {

                pgoff = linear_page_index(vma, addr);

                for (i = 0; i < nr; i++, pgoff++)

                        vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);

        } else {

                for (i = 0; i < nr; i++)

                        vec[i] = 0;

        }

        return nr;

}

/*

 * 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

 *  -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)

{

        long retval;

        unsigned long pages;

        unsigned char *tmp;

        /* Check the start address: needs to be page-aligned.. */

        if (start & ~PAGE_CACHE_MASK)

                return -EINVAL;

        /* ..and we need to be passed a valid user-space range */

        if (!access_ok(VERIFY_READ, (void __user *) start, len))

                return -ENOMEM;

        /* This also avoids any overflows on PAGE_CACHE_ALIGN */

        pages = len >> PAGE_SHIFT;

        pages += (len & ~PAGE_MASK) != 0;

        if (!access_ok(VERIFY_WRITE, vec, pages))

                return -EFAULT;

        tmp = (void *) __get_free_page(GFP_USER);

        if (!tmp)

                return -EAGAIN;

        retval = 0;

        while (pages) {

                /*

                 * Do at most PAGE_SIZE entries per iteration, due to

                 * the temporary buffer size.

                 */

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

                retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));

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

                if (retval <= 0)

                        break;

                if (copy_to_user(vec, tmp, retval)) {

                        retval = -EFAULT;

                        break;

                }

                pages -= retval;

                vec += retval;

                start += retval << PAGE_SHIFT;

                retval = 0;

        }

        free_page((unsigned long) tmp);

        return retval;

}