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  */
  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 /*
  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  */
  46 static 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  */
 112 asmlinkage 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 }