LXR linux/mm/mincore.c

   1/*
   2 *      linux/mm/mincore.c
   3 *
   4 * Copyright (C) 1994-2006  Linus Torvalds
   5 */
   6
   7/*
   8 * The mincore() system call.
   9 */
  10#include <linux/slab.h>
  11#include <linux/pagemap.h>
  12#include <linux/mm.h>
  13#include <linux/mman.h>
  14#include <linux/syscalls.h>
  15
  16#include <asm/uaccess.h>
  17#include <asm/pgtable.h>
  18
  19/*
  20 * Later we can get more picky about what "in core" means precisely.
  21 * For now, simply check to see if the page is in the page cache,
  22 * and is up to date; i.e. that no page-in operation would be required
  23 * at this time if an application were to map and access this page.
  24 */
  25static unsigned char mincore_page(struct vm_area_struct * vma,
  26        unsigned long pgoff)
  27{
  28        unsigned char present = 0;
  29        struct address_space * as = vma->vm_file->f_mapping;
  30        struct page * page;
  31
  32        page = find_get_page(as, pgoff);
  33        if (page) {
  34                present = PageUptodate(page);
  35                page_cache_release(page);
  36        }
  37
  38        return present;
  39}
  40
  41/*
  42 * Do a chunk of "sys_mincore()". We've already checked
  43 * all the arguments, we hold the mmap semaphore: we should
  44 * just return the amount of info we're asked for.
  45 */
  46static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
  47{
  48        unsigned long i, nr, pgoff;
  49        struct vm_area_struct *vma = find_vma(current->mm, addr);
  50
  51        /*
  52         * find_vma() didn't find anything above us, or we're
  53         * in an unmapped hole in the address space: ENOMEM.
  54         */
  55        if (!vma || addr < vma->vm_start)
  56                return -ENOMEM;
  57
  58        /*
  59         * Ok, got it. But check whether it's a segment we support
  60         * mincore() on. Right now, we don't do any anonymous mappings.
  61         *
  62         * FIXME: This is just stupid. And returning ENOMEM is 
  63         * stupid too. We should just look at the page tables. But
  64         * this is what we've traditionally done, so we'll just
  65         * continue doing it.
  66         */
  67        if (!vma->vm_file)
  68                return -ENOMEM;
  69
  70        /*
  71         * Calculate how many pages there are left in the vma, and
  72         * what the pgoff is for our address.
  73         */
  74        nr = (vma->vm_end - addr) >> PAGE_SHIFT;
  75        if (nr > pages)
  76                nr = pages;
  77
  78        pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
  79        pgoff += vma->vm_pgoff;
  80
  81        /* And then we just fill the sucker in.. */
  82        for (i = 0 ; i < nr; i++, pgoff++)
  83                vec[i] = mincore_page(vma, pgoff);
  84
  85        return nr;
  86}
  87
  88/*
  89 * The mincore(2) system call.
  90 *
  91 * mincore() returns the memory residency status of the pages in the
  92 * current process's address space specified by [addr, addr + len).
  93 * The status is returned in a vector of bytes.  The least significant
  94 * bit of each byte is 1 if the referenced page is in memory, otherwise
  95 * it is zero.
  96 *
  97 * Because the status of a page can change after mincore() checks it
  98 * but before it returns to the application, the returned vector may
  99 * contain stale information.  Only locked pages are guaranteed to
 100 * remain in memory.
 101 *
 102 * return values:
 103 *  zero    - success
 104 *  -EFAULT - vec points to an illegal address
 105 *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 106 *  -ENOMEM - Addresses in the range [addr, addr + len] are
 107 *              invalid for the address space of this process, or
 108 *              specify one or more pages which are not currently
 109 *              mapped
 110 *  -EAGAIN - A kernel resource was temporarily unavailable.
 111 */
 112asmlinkage long sys_mincore(unsigned long start, size_t len,
 113        unsigned char __user * vec)
 114{
 115        long retval;
 116        unsigned long pages;
 117        unsigned char *tmp;
 118
 119        /* Check the start address: needs to be page-aligned.. */
 120        if (start & ~PAGE_CACHE_MASK)
 121                return -EINVAL;
 122
 123        /* ..and we need to be passed a valid user-space range */
 124        if (!access_ok(VERIFY_READ, (void __user *) start, len))
 125                return -ENOMEM;
 126
 127        /* This also avoids any overflows on PAGE_CACHE_ALIGN */
 128        pages = len >> PAGE_SHIFT;
 129        pages += (len & ~PAGE_MASK) != 0;
 130
 131        if (!access_ok(VERIFY_WRITE, vec, pages))
 132                return -EFAULT;
 133
 134        tmp = (void *) __get_free_page(GFP_USER);
 135        if (!tmp)
 136                return -EAGAIN;
 137
 138        retval = 0;
 139        while (pages) {
 140                /*
 141                 * Do at most PAGE_SIZE entries per iteration, due to
 142                 * the temporary buffer size.
 143                 */
 144                down_read(&current->mm->mmap_sem);
 145                retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
 146                up_read(&current->mm->mmap_sem);
 147
 148                if (retval <= 0)
 149                        break;
 150                if (copy_to_user(vec, tmp, retval)) {
 151                        retval = -EFAULT;
 152                        break;
 153                }
 154                pages -= retval;
 155                vec += retval;
 156                start += retval << PAGE_SHIFT;
 157                retval = 0;
 158        }
 159        free_page((unsigned long) tmp);
 160        return retval;
 161}
 162