lib/sg_split.c

   1 /*
   2  * Copyright (C) 2015 Robert Jarzmik <robert.jarzmik@free.fr>
   3  *
   4  * Scatterlist splitting helpers.
   5  *
   6  * This source code is licensed under the GNU General Public License,
   7  * Version 2. See the file COPYING for more details.
   8  */
   9
  10 #include <linux/scatterlist.h>
  11 #include <linux/slab.h>
  12
  13 struct sg_splitter {
  14         struct scatterlist *in_sg0;
  15         int nents;
  16         off_t skip_sg0;
  17         unsigned int length_last_sg;
  18
  19         struct scatterlist *out_sg;
  20 };
  21
  22 static int sg_calculate_split(struct scatterlist *in, int nents, int nb_splits,
  23                               off_t skip, const size_t *sizes,
  24                               struct sg_splitter *splitters, bool mapped)
  25 {
  26         int i;
  27         unsigned int sglen;
  28         size_t size = sizes[0], len;
  29         struct sg_splitter *curr = splitters;
  30         struct scatterlist *sg;
  31
  32         for (i = 0; i < nb_splits; i++) {
  33                 splitters[i].in_sg0 = NULL;
  34                 splitters[i].nents = 0;
  35         }
  36
  37         for_each_sg(in, sg, nents, i) {
  38                 sglen = mapped ? sg_dma_len(sg) : sg->length;
  39                 if (skip > sglen) {
  40                         skip -= sglen;
  41                         continue;
  42                 }
  43
  44                 len = min_t(size_t, size, sglen - skip);
  45                 if (!curr->in_sg0) {
  46                         curr->in_sg0 = sg;
  47                         curr->skip_sg0 = skip;
  48                 }
  49                 size -= len;
  50                 curr->nents++;
  51                 curr->length_last_sg = len;
  52
  53                 while (!size && (skip + len < sglen) && (--nb_splits > 0)) {
  54                         curr++;
  55                         size = *(++sizes);
  56                         skip += len;
  57                         len = min_t(size_t, size, sglen - skip);
  58
  59                         curr->in_sg0 = sg;
  60                         curr->skip_sg0 = skip;
  61                         curr->nents = 1;
  62                         curr->length_last_sg = len;
  63                         size -= len;
  64                 }
  65                 skip = 0;
  66
  67                 if (!size && --nb_splits > 0) {
  68                         curr++;
  69                         size = *(++sizes);
  70                 }
  71
  72                 if (!nb_splits)
  73                         break;
  74         }
  75
  76         return (size || !splitters[0].in_sg0) ? -EINVAL : 0;
  77 }
  78
  79 static void sg_split_phys(struct sg_splitter *splitters, const int nb_splits)
  80 {
  81         int i, j;
  82         struct scatterlist *in_sg, *out_sg;
  83         struct sg_splitter *split;
  84
  85         for (i = 0, split = splitters; i < nb_splits; i++, split++) {
  86                 in_sg = split->in_sg0;
  87                 out_sg = split->out_sg;
  88                 for (j = 0; j < split->nents; j++, out_sg++) {
  89                         *out_sg = *in_sg;
  90                         if (!j) {
  91                                 out_sg->offset += split->skip_sg0;
  92                                 out_sg->length -= split->skip_sg0;
  93                         } else {
  94                                 out_sg->offset = 0;
  95                         }
  96                         sg_dma_address(out_sg) = 0;
  97                         sg_dma_len(out_sg) = 0;
  98                         in_sg = sg_next(in_sg);
  99                 }
 100                 out_sg[-1].length = split->length_last_sg;
 101                 sg_mark_end(out_sg - 1);
 102         }
 103 }
 104
 105 static void sg_split_mapped(struct sg_splitter *splitters, const int nb_splits)
 106 {
 107         int i, j;
 108         struct scatterlist *in_sg, *out_sg;
 109         struct sg_splitter *split;
 110
 111         for (i = 0, split = splitters; i < nb_splits; i++, split++) {
 112                 in_sg = split->in_sg0;
 113                 out_sg = split->out_sg;
 114                 for (j = 0; j < split->nents; j++, out_sg++) {
 115                         sg_dma_address(out_sg) = sg_dma_address(in_sg);
 116                         sg_dma_len(out_sg) = sg_dma_len(in_sg);
 117                         if (!j) {
 118                                 sg_dma_address(out_sg) += split->skip_sg0;
 119                                 sg_dma_len(out_sg) -= split->skip_sg0;
 120                         }
 121                         in_sg = sg_next(in_sg);
 122                 }
 123                 sg_dma_len(--out_sg) = split->length_last_sg;
 124         }
 125 }
 126
 127 /**
 128  * sg_split - split a scatterlist into several scatterlists
 129  * @in: the input sg list
 130  * @in_mapped_nents: the result of a dma_map_sg(in, ...), or 0 if not mapped.
 131  * @skip: the number of bytes to skip in the input sg list
 132  * @nb_splits: the number of desired sg outputs
 133  * @split_sizes: the respective size of each output sg list in bytes
 134  * @out: an array where to store the allocated output sg lists
 135  * @out_mapped_nents: the resulting sg lists mapped number of sg entries. Might
 136  *                    be NULL if sglist not already mapped (in_mapped_nents = 0)
 137  * @gfp_mask: the allocation flag
 138  *
 139  * This function splits the input sg list into nb_splits sg lists, which are
 140  * allocated and stored into out.
 141  * The @in is split into :
 142  *  - @out[0], which covers bytes [@skip .. @skip + @split_sizes[0] - 1] of @in
 143  *  - @out[1], which covers bytes [@skip + split_sizes[0] ..
 144  *                                 @skip + @split_sizes[0] + @split_sizes[1] -1]
 145  * etc ...
 146  * It will be the caller's duty to kfree() out array members.
 147  *
 148  * Returns 0 upon success, or error code
 149  */
 150 int sg_split(struct scatterlist *in, const int in_mapped_nents,
 151              const off_t skip, const int nb_splits,
 152              const size_t *split_sizes,
 153              struct scatterlist **out, int *out_mapped_nents,
 154              gfp_t gfp_mask)
 155 {
 156         int i, ret;
 157         struct sg_splitter *splitters;
 158
 159         splitters = kcalloc(nb_splits, sizeof(*splitters), gfp_mask);
 160         if (!splitters)
 161                 return -ENOMEM;
 162
 163         ret = sg_calculate_split(in, sg_nents(in), nb_splits, skip, split_sizes,
 164                            splitters, false);
 165         if (ret < 0)
 166                 goto err;
 167
 168         ret = -ENOMEM;
 169         for (i = 0; i < nb_splits; i++) {
 170                 splitters[i].out_sg = kmalloc_array(splitters[i].nents,
 171                                                     sizeof(struct scatterlist),
 172                                                     gfp_mask);
 173                 if (!splitters[i].out_sg)
 174                         goto err;
 175         }
 176
 177         /*
 178          * The order of these 3 calls is important and should be kept.
 179          */
 180         sg_split_phys(splitters, nb_splits);
 181         ret = sg_calculate_split(in, in_mapped_nents, nb_splits, skip,
 182                                  split_sizes, splitters, true);
 183         if (ret < 0)
 184                 goto err;
 185         sg_split_mapped(splitters, nb_splits);
 186
 187         for (i = 0; i < nb_splits; i++) {
 188                 out[i] = splitters[i].out_sg;
 189                 if (out_mapped_nents)
 190                         out_mapped_nents[i] = splitters[i].nents;
 191         }
 192
 193         kfree(splitters);
 194         return 0;
 195
 196 err:
 197         for (i = 0; i < nb_splits; i++)
 198                 kfree(splitters[i].out_sg);
 199         kfree(splitters);
 200         return ret;
 201 }
 202 EXPORT_SYMBOL(sg_split);