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 #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  */
  25 static 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 static long mincore_vma(struct vm_area_struct * vma,
  42         unsigned long start, unsigned long end, unsigned char __user * vec)
  43 {
  44         long error, i, remaining;
  45         unsigned char * tmp;
  46
  47         error = -ENOMEM;
  48         if (!vma->vm_file)
  49                 return error;
  50
  51         start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  52         if (end > vma->vm_end)
  53                 end = vma->vm_end;
  54         end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  55
  56         error = -EAGAIN;
  57         tmp = (unsigned char *) __get_free_page(GFP_KERNEL);
  58         if (!tmp)
  59                 return error;
  60
  61         /* (end - start) is # of pages, and also # of bytes in "vec */
  62         remaining = (end - start),
  63
  64         error = 0;
  65         for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) {
  66                 int j = 0;
  67                 long thispiece = (remaining < PAGE_SIZE) ?
  68                                                 remaining : PAGE_SIZE;
  69
  70                 while (j < thispiece)
  71                         tmp[j++] = mincore_page(vma, start++);
  72
  73                 if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) {
  74                         error = -EFAULT;
  75                         break;
  76                 }
  77         }
  78
  79         free_page((unsigned long) tmp);
  80         return error;
  81 }
  82
  83 /*
  84  * The mincore(2) system call.
  85  *
  86  * mincore() returns the memory residency status of the pages in the
  87  * current process's address space specified by [addr, addr + len).
  88  * The status is returned in a vector of bytes.  The least significant
  89  * bit of each byte is 1 if the referenced page is in memory, otherwise
  90  * it is zero.
  91  *
  92  * Because the status of a page can change after mincore() checks it
  93  * but before it returns to the application, the returned vector may
  94  * contain stale information.  Only locked pages are guaranteed to
  95  * remain in memory.
  96  *
  97  * return values:
  98  *  zero    - success
  99  *  -EFAULT - vec points to an illegal address
 100  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
 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, limit;
 112         struct vm_area_struct * vma;
 113         size_t max;
 114         int unmapped_error = 0;
 115         long error;
 116
 117         /* check the arguments */
 118         if (start & ~PAGE_CACHE_MASK)
 119                 goto einval;
 120
 121         if (start < FIRST_USER_PGD_NR * PGDIR_SIZE)
 122                 goto enomem;
 123
 124         limit = TASK_SIZE;
 125         if (start >= limit)
 126                 goto enomem;
 127
 128         if (!len)
 129                 return 0;
 130
 131         max = limit - start;
 132         len = PAGE_CACHE_ALIGN(len);
 133         if (len > max || !len)
 134                 goto enomem;
 135
 136         end = start + len;
 137
 138         /* check the output buffer whilst holding the lock */
 139         error = -EFAULT;
 140         down_read(&current->mm->mmap_sem);
 141
 142         if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
 143                 goto out;
 144
 145         /*
 146          * If the interval [start,end) covers some unmapped address
 147          * ranges, just ignore them, but return -ENOMEM at the end.
 148          */
 149         error = 0;
 150
 151         vma = find_vma(current->mm, start);
 152         while (vma) {
 153                 /* Here start < vma->vm_end. */
 154                 if (start < vma->vm_start) {
 155                         unmapped_error = -ENOMEM;
 156                         start = vma->vm_start;
 157                 }
 158
 159                 /* Here vma->vm_start <= start < vma->vm_end. */
 160                 if (end <= vma->vm_end) {
 161                         if (start < end) {
 162                                 error = mincore_vma(vma, start, end,
 163                                                         &vec[index]);
 164                                 if (error)
 165                                         goto out;
 166                         }
 167                         error = unmapped_error;
 168                         goto out;
 169                 }
 170
 171                 /* Here vma->vm_start <= start < vma->vm_end < end. */
 172                 error = mincore_vma(vma, start, vma->vm_end, &vec[index]);
 173                 if (error)
 174                         goto out;
 175                 index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT;
 176                 start = vma->vm_end;
 177                 vma = vma->vm_next;
 178         }
 179
 180         /* we found a hole in the area queried if we arrive here */
 181         error = -ENOMEM;
 182
 183 out:
 184         up_read(&current->mm->mmap_sem);
 185         return error;
 186
 187 einval:
 188         return -EINVAL;
 189 enomem:
 190         return -ENOMEM;
 191 }