1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Copyright (C) 2015 Robert Jarzmik <robert.jarzmik@free.fr> 4 * 5 * Scatterlist splitting helpers. 6 */ 7 8 #include <linux/scatterlist.h> 9 #include <linux/slab.h> 10 11 struct sg_splitter { 12 struct scatterlist *in_sg0; 13 int nents; 14 off_t skip_sg0; 15 unsigned int length_last_sg; 16 17 struct scatterlist *out_sg; 18 }; 19 20 static int sg_calculate_split(struct scatterlist *in, int nents, int nb_splits, 21 off_t skip, const size_t *sizes, 22 struct sg_splitter *splitters, bool mapped) 23 { 24 int i; 25 unsigned int sglen; 26 size_t size = sizes[0], len; 27 struct sg_splitter *curr = splitters; 28 struct scatterlist *sg; 29 30 for (i = 0; i < nb_splits; i++) { 31 splitters[i].in_sg0 = NULL; 32 splitters[i].nents = 0; 33 } 34 35 for_each_sg(in, sg, nents, i) { 36 sglen = mapped ? sg_dma_len(sg) : sg->length; 37 if (skip > sglen) { 38 skip -= sglen; 39 continue; 40 } 41 42 len = min_t(size_t, size, sglen - skip); 43 if (!curr->in_sg0) { 44 curr->in_sg0 = sg; 45 curr->skip_sg0 = skip; 46 } 47 size -= len; 48 curr->nents++; 49 curr->length_last_sg = len; 50 51 while (!size && (skip + len < sglen) && (--nb_splits > 0)) { 52 curr++; 53 size = *(++sizes); 54 skip += len; 55 len = min_t(size_t, size, sglen - skip); 56 57 curr->in_sg0 = sg; 58 curr->skip_sg0 = skip; 59 curr->nents = 1; 60 curr->length_last_sg = len; 61 size -= len; 62 } 63 skip = 0; 64 65 if (!size && --nb_splits > 0) { 66 curr++; 67 size = *(++sizes); 68 } 69 70 if (!nb_splits) 71 break; 72 } 73 74 return (size || !splitters[0].in_sg0) ? -EINVAL : 0; 75 } 76 77 static void sg_split_phys(struct sg_splitter *splitters, const int nb_splits) 78 { 79 int i, j; 80 struct scatterlist *in_sg, *out_sg; 81 struct sg_splitter *split; 82 83 for (i = 0, split = splitters; i < nb_splits; i++, split++) { 84 in_sg = split->in_sg0; 85 out_sg = split->out_sg; 86 for (j = 0; j < split->nents; j++, out_sg++) { 87 *out_sg = *in_sg; 88 if (!j) { 89 out_sg->offset += split->skip_sg0; 90 out_sg->length -= split->skip_sg0; 91 } else { 92 out_sg->offset = 0; 93 } 94 sg_dma_address(out_sg) = 0; 95 sg_dma_len(out_sg) = 0; 96 in_sg = sg_next(in_sg); 97 } 98 out_sg[-1].length = split->length_last_sg; 99 sg_mark_end(out_sg - 1); 100 } 101 } 102 103 static void sg_split_mapped(struct sg_splitter *splitters, const int nb_splits) 104 { 105 int i, j; 106 struct scatterlist *in_sg, *out_sg; 107 struct sg_splitter *split; 108 109 for (i = 0, split = splitters; i < nb_splits; i++, split++) { 110 in_sg = split->in_sg0; 111 out_sg = split->out_sg; 112 for (j = 0; j < split->nents; j++, out_sg++) { 113 sg_dma_address(out_sg) = sg_dma_address(in_sg); 114 sg_dma_len(out_sg) = sg_dma_len(in_sg); 115 if (!j) { 116 sg_dma_address(out_sg) += split->skip_sg0; 117 sg_dma_len(out_sg) -= split->skip_sg0; 118 } 119 in_sg = sg_next(in_sg); 120 } 121 sg_dma_len(--out_sg) = split->length_last_sg; 122 } 123 } 124 125 /** 126 * sg_split - split a scatterlist into several scatterlists 127 * @in: the input sg list 128 * @in_mapped_nents: the result of a dma_map_sg(in, ...), or 0 if not mapped. 129 * @skip: the number of bytes to skip in the input sg list 130 * @nb_splits: the number of desired sg outputs 131 * @split_sizes: the respective size of each output sg list in bytes 132 * @out: an array where to store the allocated output sg lists 133 * @out_mapped_nents: the resulting sg lists mapped number of sg entries. Might 134 * be NULL if sglist not already mapped (in_mapped_nents = 0) 135 * @gfp_mask: the allocation flag 136 * 137 * This function splits the input sg list into nb_splits sg lists, which are 138 * allocated and stored into out. 139 * The @in is split into : 140 * - @out[0], which covers bytes [@skip .. @skip + @split_sizes[0] - 1] of @in 141 * - @out[1], which covers bytes [@skip + split_sizes[0] .. 142 * @skip + @split_sizes[0] + @split_sizes[1] -1] 143 * etc ... 144 * It will be the caller's duty to kfree() out array members. 145 * 146 * Returns 0 upon success, or error code 147 */ 148 int sg_split(struct scatterlist *in, const int in_mapped_nents, 149 const off_t skip, const int nb_splits, 150 const size_t *split_sizes, 151 struct scatterlist **out, int *out_mapped_nents, 152 gfp_t gfp_mask) 153 { 154 int i, ret; 155 struct sg_splitter *splitters; 156 157 splitters = kcalloc(nb_splits, sizeof(*splitters), gfp_mask); 158 if (!splitters) 159 return -ENOMEM; 160 161 ret = sg_calculate_split(in, sg_nents(in), nb_splits, skip, split_sizes, 162 splitters, false); 163 if (ret < 0) 164 goto err; 165 166 ret = -ENOMEM; 167 for (i = 0; i < nb_splits; i++) { 168 splitters[i].out_sg = kmalloc_array(splitters[i].nents, 169 sizeof(struct scatterlist), 170 gfp_mask); 171 if (!splitters[i].out_sg) 172 goto err; 173 } 174 175 /* 176 * The order of these 3 calls is important and should be kept. 177 */ 178 sg_split_phys(splitters, nb_splits); 179 ret = sg_calculate_split(in, in_mapped_nents, nb_splits, skip, 180 split_sizes, splitters, true); 181 if (ret < 0) 182 goto err; 183 sg_split_mapped(splitters, nb_splits); 184 185 for (i = 0; i < nb_splits; i++) { 186 out[i] = splitters[i].out_sg; 187 if (out_mapped_nents) 188 out_mapped_nents[i] = splitters[i].nents; 189 } 190 191 kfree(splitters); 192 return 0; 193 194 err: 195 for (i = 0; i < nb_splits; i++) 196 kfree(splitters[i].out_sg); 197 kfree(splitters); 198 return ret; 199 } 200 EXPORT_SYMBOL(sg_split); 201