mm/filemap.h

   1 /*
   2  *      linux/mm/filemap.h
   3  *
   4  * Copyright (C) 1994-1999  Linus Torvalds
   5  */
   6
   7 #ifndef __FILEMAP_H
   8 #define __FILEMAP_H
   9
  10 #include <linux/types.h>
  11 #include <linux/fs.h>
  12 #include <linux/mm.h>
  13 #include <linux/highmem.h>
  14 #include <linux/uio.h>
  15 #include <linux/uaccess.h>
  16
  17 size_t
  18 __filemap_copy_from_user_iovec_inatomic(char *vaddr,
  19                                         const struct iovec *iov,
  20                                         size_t base,
  21                                         size_t bytes);
  22
  23 /*
  24  * Copy as much as we can into the page and return the number of bytes which
  25  * were sucessfully copied.  If a fault is encountered then clear the page
  26  * out to (offset+bytes) and return the number of bytes which were copied.
  27  *
  28  * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache
  29  * to *NOT* zero any tail of the buffer that it failed to copy.  If it does,
  30  * and if the following non-atomic copy succeeds, then there is a small window
  31  * where the target page contains neither the data before the write, nor the
  32  * data after the write (it contains zero).  A read at this time will see
  33  * data that is inconsistent with any ordering of the read and the write.
  34  * (This has been detected in practice).
  35  */
  36 static inline size_t
  37 filemap_copy_from_user(struct page *page, unsigned long offset,
  38                         const char __user *buf, unsigned bytes)
  39 {
  40         char *kaddr;
  41         int left;
  42
  43         kaddr = kmap_atomic(page, KM_USER0);
  44         left = __copy_from_user_inatomic_nocache(kaddr + offset, buf, bytes);
  45         kunmap_atomic(kaddr, KM_USER0);
  46
  47         if (left != 0) {
  48                 /* Do it the slow way */
  49                 kaddr = kmap(page);
  50                 left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
  51                 kunmap(page);
  52         }
  53         return bytes - left;
  54 }
  55
  56 /*
  57  * This has the same sideeffects and return value as filemap_copy_from_user().
  58  * The difference is that on a fault we need to memset the remainder of the
  59  * page (out to offset+bytes), to emulate filemap_copy_from_user()'s
  60  * single-segment behaviour.
  61  */
  62 static inline size_t
  63 filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
  64                         const struct iovec *iov, size_t base, size_t bytes)
  65 {
  66         char *kaddr;
  67         size_t copied;
  68
  69         kaddr = kmap_atomic(page, KM_USER0);
  70         copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
  71                                                          base, bytes);
  72         kunmap_atomic(kaddr, KM_USER0);
  73         if (copied != bytes) {
  74                 kaddr = kmap(page);
  75                 copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
  76                                                                  base, bytes);
  77                 if (bytes - copied)
  78                         memset(kaddr + offset + copied, 0, bytes - copied);
  79                 kunmap(page);
  80         }
  81         return copied;
  82 }
  83
  84 static inline void
  85 filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes)
  86 {
  87         const struct iovec *iov = *iovp;
  88         size_t base = *basep;
  89
  90         do {
  91                 int copy = min(bytes, iov->iov_len - base);
  92
  93                 bytes -= copy;
  94                 base += copy;
  95                 if (iov->iov_len == base) {
  96                         iov++;
  97                         base = 0;
  98                 }
  99         } while (bytes);
 100         *iovp = iov;
 101         *basep = base;
 102 }
 103 #endif