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 if (in_mapped_nents) {
180 ret = sg_calculate_split(in, in_mapped_nents, nb_splits, skip,
181 split_sizes, splitters, true);
182 if (ret < 0)
183 goto err;
184 sg_split_mapped(splitters, nb_splits);
185 }
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);
203
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