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
13struct 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
22static 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
79static 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
105static 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 */
150int 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
196err:
197 for (i = 0; i < nb_splits; i++)
198 kfree(splitters[i].out_sg);
199 kfree(splitters);
200 return ret;
201}
202EXPORT_SYMBOL(sg_split);
203