include/linux/bvec.h

   1 /*
   2  * bvec iterator
   3  *
   4  * Copyright (C) 2001 Ming Lei <ming.lei@canonical.com>
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public Licens
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
  19  */
  20 #ifndef __LINUX_BVEC_ITER_H
  21 #define __LINUX_BVEC_ITER_H
  22
  23 #include <linux/kernel.h>
  24 #include <linux/bug.h>
  25 #include <linux/errno.h>
  26
  27 /*
  28  * was unsigned short, but we might as well be ready for > 64kB I/O pages
  29  */
  30 struct bio_vec {
  31         struct page     *bv_page;
  32         unsigned int    bv_len;
  33         unsigned int    bv_offset;
  34 };
  35
  36 struct bvec_iter {
  37         sector_t                bi_sector;      /* device address in 512 byte
  38                                                    sectors */
  39         unsigned int            bi_size;        /* residual I/O count */
  40
  41         unsigned int            bi_idx;         /* current index into bvl_vec */
  42
  43         unsigned int            bi_done;        /* number of bytes completed */
  44
  45         unsigned int            bi_bvec_done;   /* number of bytes completed in
  46                                                    current bvec */
  47 };
  48
  49 /*
  50  * various member access, note that bio_data should of course not be used
  51  * on highmem page vectors
  52  */
  53 #define __bvec_iter_bvec(bvec, iter)    (&(bvec)[(iter).bi_idx])
  54
  55 #define bvec_iter_page(bvec, iter)                              \
  56         (__bvec_iter_bvec((bvec), (iter))->bv_page)
  57
  58 #define bvec_iter_len(bvec, iter)                               \
  59         min((iter).bi_size,                                     \
  60             __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)
  61
  62 #define bvec_iter_offset(bvec, iter)                            \
  63         (__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)
  64
  65 #define bvec_iter_bvec(bvec, iter)                              \
  66 ((struct bio_vec) {                                             \
  67         .bv_page        = bvec_iter_page((bvec), (iter)),       \
  68         .bv_len         = bvec_iter_len((bvec), (iter)),        \
  69         .bv_offset      = bvec_iter_offset((bvec), (iter)),     \
  70 })
  71
  72 static inline bool bvec_iter_advance(const struct bio_vec *bv,
  73                 struct bvec_iter *iter, unsigned bytes)
  74 {
  75         if (WARN_ONCE(bytes > iter->bi_size,
  76                      "Attempted to advance past end of bvec iter\n")) {
  77                 iter->bi_size = 0;
  78                 return false;
  79         }
  80
  81         while (bytes) {
  82                 unsigned iter_len = bvec_iter_len(bv, *iter);
  83                 unsigned len = min(bytes, iter_len);
  84
  85                 bytes -= len;
  86                 iter->bi_size -= len;
  87                 iter->bi_bvec_done += len;
  88                 iter->bi_done += len;
  89
  90                 if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
  91                         iter->bi_bvec_done = 0;
  92                         iter->bi_idx++;
  93                 }
  94         }
  95         return true;
  96 }
  97
  98 static inline bool bvec_iter_rewind(const struct bio_vec *bv,
  99                                      struct bvec_iter *iter,
 100                                      unsigned int bytes)
 101 {
 102         while (bytes) {
 103                 unsigned len = min(bytes, iter->bi_bvec_done);
 104
 105                 if (iter->bi_bvec_done == 0) {
 106                         if (WARN_ONCE(iter->bi_idx == 0,
 107                                       "Attempted to rewind iter beyond "
 108                                       "bvec's boundaries\n")) {
 109                                 return false;
 110                         }
 111                         iter->bi_idx--;
 112                         iter->bi_bvec_done = __bvec_iter_bvec(bv, *iter)->bv_len;
 113                         continue;
 114                 }
 115                 bytes -= len;
 116                 iter->bi_size += len;
 117                 iter->bi_bvec_done -= len;
 118         }
 119         return true;
 120 }
 121
 122 #define for_each_bvec(bvl, bio_vec, iter, start)                        \
 123         for (iter = (start);                                            \
 124              (iter).bi_size &&                                          \
 125                 ((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
 126              bvec_iter_advance((bio_vec), &(iter), (bvl).bv_len))
 127
 128 #endif /* __LINUX_BVEC_ITER_H */