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_bvec_done;   /* number of bytes completed in
  44                                                    current bvec */
  45 };
  46
  47 /*
  48  * various member access, note that bio_data should of course not be used
  49  * on highmem page vectors
  50  */
  51 #define __bvec_iter_bvec(bvec, iter)    (&(bvec)[(iter).bi_idx])
  52
  53 #define bvec_iter_page(bvec, iter)                              \
  54         (__bvec_iter_bvec((bvec), (iter))->bv_page)
  55
  56 #define bvec_iter_len(bvec, iter)                               \
  57         min((iter).bi_size,                                     \
  58             __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)
  59
  60 #define bvec_iter_offset(bvec, iter)                            \
  61         (__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)
  62
  63 #define bvec_iter_bvec(bvec, iter)                              \
  64 ((struct bio_vec) {                                             \
  65         .bv_page        = bvec_iter_page((bvec), (iter)),       \
  66         .bv_len         = bvec_iter_len((bvec), (iter)),        \
  67         .bv_offset      = bvec_iter_offset((bvec), (iter)),     \
  68 })
  69
  70 static inline bool bvec_iter_advance(const struct bio_vec *bv,
  71                 struct bvec_iter *iter, unsigned bytes)
  72 {
  73         if (WARN_ONCE(bytes > iter->bi_size,
  74                      "Attempted to advance past end of bvec iter\n")) {
  75                 iter->bi_size = 0;
  76                 return false;
  77         }
  78
  79         while (bytes) {
  80                 unsigned iter_len = bvec_iter_len(bv, *iter);
  81                 unsigned len = min(bytes, iter_len);
  82
  83                 bytes -= len;
  84                 iter->bi_size -= len;
  85                 iter->bi_bvec_done += len;
  86
  87                 if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
  88                         iter->bi_bvec_done = 0;
  89                         iter->bi_idx++;
  90                 }
  91         }
  92         return true;
  93 }
  94
  95 static inline bool bvec_iter_rewind(const struct bio_vec *bv,
  96                                      struct bvec_iter *iter,
  97                                      unsigned int bytes)
  98 {
  99         while (bytes) {
 100                 unsigned len = min(bytes, iter->bi_bvec_done);
 101
 102                 if (iter->bi_bvec_done == 0) {
 103                         if (WARN_ONCE(iter->bi_idx == 0,
 104                                       "Attempted to rewind iter beyond "
 105                                       "bvec's boundaries\n")) {
 106                                 return false;
 107                         }
 108                         iter->bi_idx--;
 109                         iter->bi_bvec_done = __bvec_iter_bvec(bv, *iter)->bv_len;
 110                         continue;
 111                 }
 112                 bytes -= len;
 113                 iter->bi_size += len;
 114                 iter->bi_bvec_done -= len;
 115         }
 116         return true;
 117 }
 118
 119 #define for_each_bvec(bvl, bio_vec, iter, start)                        \
 120         for (iter = (start);                                            \
 121              (iter).bi_size &&                                          \
 122                 ((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
 123              bvec_iter_advance((bio_vec), &(iter), (bvl).bv_len))
 124
 125 /* for iterating one bio from start to end */
 126 #define BVEC_ITER_ALL_INIT (struct bvec_iter)                           \
 127 {                                                                       \
 128         .bi_sector      = 0,                                            \
 129         .bi_size        = UINT_MAX,                                     \
 130         .bi_idx         = 0,                                            \
 131         .bi_bvec_done   = 0,                                            \
 132 }
 133
 134 #endif /* __LINUX_BVEC_ITER_H */