mm/mincore.c

   1 /*
   2  *      linux/mm/mincore.c
   3  *
   4  * Copyright (C) 1994-1999  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
  15 #include <asm/uaccess.h>
  16 #include <asm/pgtable.h>
  17
  18 /*
  19  * Later we can get more picky about what "in core" means precisely.
  20  * For now, simply check to see if the page is in the page cache,
  21  * and is up to date; i.e. that no page-in operation would be required
  22  * at this time if an application were to map and access this page.
  23  */
  24 static unsigned char mincore_page(struct vm_area_struct * vma,
  25         unsigned long pgoff)
  26 {
  27         unsigned char present = 0;
  28         struct address_space * as = vma->vm_file->f_mapping;
  29         struct page * page;
  30
  31         page = find_get_page(as, pgoff);
  32         if (page) {
  33                 present = PageUptodate(page);
  34                 page_cache_release(page);
  35         }
  36
  37         return present;
  38 }
  39
  40 static long mincore_vma(struct vm_area_struct * vma,
  41         unsigned long start, unsigned long end, unsigned char __user * vec)
  42 {
  43         long error, i, remaining;
  44         unsigned char * tmp;
  45
  46         error = -ENOMEM;
  47         if (!vma->vm_file)
  48                 return error;
  49
  50         start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  51         if (end > vma->vm_end)
  52                 end = vma->vm_end;
  53         end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  54
  55         error = -EAGAIN;
  56         tmp = (unsigned char *) __get_free_page(GFP_KERNEL);
  57         if (!tmp)
  58                 return error;
  59
  60         /* (end - start) is # of pages, and also # of bytes in "vec */
  61         remaining = (end - start),
  62
  63         error = 0;
  64         for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) {
  65                 int j = 0;
  66                 long thispiece = (remaining < PAGE_SIZE) ?
  67                                                 remaining : PAGE_SIZE;
  68
  69                 while (j < thispiece)
  70                         tmp[j++] = mincore_page(vma, start++);
  71
  72                 if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) {
  73                         error = -EFAULT;
  74                         break;
  75                 }
  76         }
  77
  78         free_page((unsigned long) tmp);
  79         return error;
  80 }
  81
  82 /*
  83  * The mincore(2) system call.
  84  *
  85  * mincore() returns the memory residency status of the pages in the
  86  * current process's address space specified by [addr, addr + len).
  87  * The status is returned in a vector of bytes.  The least significant
  88  * bit of each byte is 1 if the referenced page is in memory, otherwise
  89  * it is zero.
  90  *
  91  * Because the status of a page can change after mincore() checks it
  92  * but before it returns to the application, the returned vector may
  93  * contain stale information.  Only locked pages are guaranteed to
  94  * remain in memory.
  95  *
  96  * return values:
  97  *  zero    - success
  98  *  -EFAULT - vec points to an illegal address
  99  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE,
 100  *              or len has a nonpositive value
 101  *  -ENOMEM - Addresses in the range [addr, addr + len] are
 102  *              invalid for the address space of this process, or
 103  *              specify one or more pages which are not currently
 104  *              mapped
 105  *  -EAGAIN - A kernel resource was temporarily unavailable.
 106  */
 107 asmlinkage long sys_mincore(unsigned long start, size_t len,
 108         unsigned char __user * vec)
 109 {
 110         int index = 0;
 111         unsigned long end;
 112         struct vm_area_struct * vma;
 113         int unmapped_error = 0;
 114         long error = -EINVAL;
 115
 116         down_read(&current->mm->mmap_sem);
 117
 118         if (start & ~PAGE_CACHE_MASK)
 119                 goto out;
 120         len = (len + ~PAGE_CACHE_MASK) & PAGE_CACHE_MASK;
 121         end = start + len;
 122         if (end < start)
 123                 goto out;
 124
 125         error = -EFAULT;
 126         if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
 127                 goto out;
 128
 129         error = 0;
 130         if (end == start)
 131                 goto out;
 132
 133         /*
 134          * If the interval [start,end) covers some unmapped address
 135          * ranges, just ignore them, but return -ENOMEM at the end.
 136          */
 137         vma = find_vma(current->mm, start);
 138         for (;;) {
 139                 /* Still start < end. */
 140                 error = -ENOMEM;
 141                 if (!vma)
 142                         goto out;
 143
 144                 /* Here start < vma->vm_end. */
 145                 if (start < vma->vm_start) {
 146                         unmapped_error = -ENOMEM;
 147                         start = vma->vm_start;
 148                 }
 149
 150                 /* Here vma->vm_start <= start < vma->vm_end. */
 151                 if (end <= vma->vm_end) {
 152                         if (start < end) {
 153                                 error = mincore_vma(vma, start, end,
 154                                                         &vec[index]);
 155                                 if (error)
 156                                         goto out;
 157                         }
 158                         error = unmapped_error;
 159                         goto out;
 160                 }
 161
 162                 /* Here vma->vm_start <= start < vma->vm_end < end. */
 163                 error = mincore_vma(vma, start, vma->vm_end, &vec[index]);
 164                 if (error)
 165                         goto out;
 166                 index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT;
 167                 start = vma->vm_end;
 168                 vma = vma->vm_next;
 169         }
 170
 171 out:
 172         up_read(&current->mm->mmap_sem);
 173         return error;
 174 }