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