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 #include <linux/mm.h>
  27
  28 /*
  29  * was unsigned short, but we might as well be ready for > 64kB I/O pages
  30  */
  31 struct bio_vec {
  32         struct page     *bv_page;
  33         unsigned int    bv_len;
  34         unsigned int    bv_offset;
  35 };
  36
  37 struct bvec_iter {
  38         sector_t                bi_sector;      /* device address in 512 byte
  39                                                    sectors */
  40         unsigned int            bi_size;        /* residual I/O count */
  41
  42         unsigned int            bi_idx;         /* current index into bvl_vec */
  43
  44         unsigned int            bi_done;        /* number of bytes completed */
  45
  46         unsigned int            bi_bvec_done;   /* number of bytes completed in
  47                                                    current bvec */
  48 };
  49
  50 /*
  51  * various member access, note that bio_data should of course not be used
  52  * on highmem page vectors
  53  */
  54 #define __bvec_iter_bvec(bvec, iter)    (&(bvec)[(iter).bi_idx])
  55
  56 /* multi-page (mp_bvec) helpers */
  57 #define mp_bvec_iter_page(bvec, iter)                           \
  58         (__bvec_iter_bvec((bvec), (iter))->bv_page)
  59
  60 #define mp_bvec_iter_len(bvec, iter)                            \
  61         min((iter).bi_size,                                     \
  62             __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)
  63
  64 #define mp_bvec_iter_offset(bvec, iter)                         \
  65         (__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)
  66
  67 #define mp_bvec_iter_page_idx(bvec, iter)                       \
  68         (mp_bvec_iter_offset((bvec), (iter)) / PAGE_SIZE)
  69
  70 #define mp_bvec_iter_bvec(bvec, iter)                           \
  71 ((struct bio_vec) {                                             \
  72         .bv_page        = mp_bvec_iter_page((bvec), (iter)),    \
  73         .bv_len         = mp_bvec_iter_len((bvec), (iter)),     \
  74         .bv_offset      = mp_bvec_iter_offset((bvec), (iter)),  \
  75 })
  76
  77 /* For building single-page bvec in flight */
  78  #define bvec_iter_offset(bvec, iter)                           \
  79         (mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)
  80
  81 #define bvec_iter_len(bvec, iter)                               \
  82         min_t(unsigned, mp_bvec_iter_len((bvec), (iter)),               \
  83               PAGE_SIZE - bvec_iter_offset((bvec), (iter)))
  84
  85 #define bvec_iter_page(bvec, iter)                              \
  86         nth_page(mp_bvec_iter_page((bvec), (iter)),             \
  87                  mp_bvec_iter_page_idx((bvec), (iter)))
  88
  89 #define bvec_iter_bvec(bvec, iter)                              \
  90 ((struct bio_vec) {                                             \
  91         .bv_page        = bvec_iter_page((bvec), (iter)),       \
  92         .bv_len         = bvec_iter_len((bvec), (iter)),        \
  93         .bv_offset      = bvec_iter_offset((bvec), (iter)),     \
  94 })
  95
  96 static inline bool bvec_iter_advance(const struct bio_vec *bv,
  97                 struct bvec_iter *iter, unsigned bytes)
  98 {
  99         if (WARN_ONCE(bytes > iter->bi_size,
 100                      "Attempted to advance past end of bvec iter\n")) {
 101                 iter->bi_size = 0;
 102                 return false;
 103         }
 104
 105         while (bytes) {
 106                 unsigned iter_len = bvec_iter_len(bv, *iter);
 107                 unsigned len = min(bytes, iter_len);
 108
 109                 bytes -= len;
 110                 iter->bi_size -= len;
 111                 iter->bi_bvec_done += len;
 112                 iter->bi_done += len;
 113
 114                 if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
 115                         iter->bi_bvec_done = 0;
 116                         iter->bi_idx++;
 117                 }
 118         }
 119         return true;
 120 }
 121
 122 static inline bool bvec_iter_rewind(const struct bio_vec *bv,
 123                                      struct bvec_iter *iter,
 124                                      unsigned int bytes)
 125 {
 126         while (bytes) {
 127                 unsigned len = min(bytes, iter->bi_bvec_done);
 128
 129                 if (iter->bi_bvec_done == 0) {
 130                         if (WARN_ONCE(iter->bi_idx == 0,
 131                                       "Attempted to rewind iter beyond "
 132                                       "bvec's boundaries\n")) {
 133                                 return false;
 134                         }
 135                         iter->bi_idx--;
 136                         iter->bi_bvec_done = __bvec_iter_bvec(bv, *iter)->bv_len;
 137                         continue;
 138                 }
 139                 bytes -= len;
 140                 iter->bi_size += len;
 141                 iter->bi_bvec_done -= len;
 142         }
 143         return true;
 144 }
 145
 146 static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
 147 {
 148         iter->bi_bvec_done = 0;
 149         iter->bi_idx++;
 150 }
 151
 152 #define for_each_bvec(bvl, bio_vec, iter, start)                        \
 153         for (iter = (start);                                            \
 154              (iter).bi_size &&                                          \
 155                 ((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
 156              (bvl).bv_len ? (void)bvec_iter_advance((bio_vec), &(iter), \
 157                      (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
 158
 159 #endif /* __LINUX_BVEC_ITER_H */