aboutsummaryrefslogtreecommitdiff
path: root/lib/sg_split.c
blob: 60a0babebf2efca4f94ebcf3bf160be8715c2a30 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2015 Robert Jarzmik <robert.jarzmik@free.fr>
 *
 * Scatterlist splitting helpers.
 */

#include <linux/scatterlist.h>
#include <linux/slab.h>

struct sg_splitter {
	struct scatterlist *in_sg0;
	int nents;
	off_t skip_sg0;
	unsigned int length_last_sg;

	struct scatterlist *out_sg;
};

static int sg_calculate_split(struct scatterlist *in, int nents, int nb_splits,
			      off_t skip, const size_t *sizes,
			      struct sg_splitter *splitters, bool mapped)
{
	int i;
	unsigned int sglen;
	size_t size = sizes[0], len;
	struct sg_splitter *curr = splitters;
	struct scatterlist *sg;

	for (i = 0; i < nb_splits; i++) {
		splitters[i].in_sg0 = NULL;
		splitters[i].nents = 0;
	}

	for_each_sg(in, sg, nents, i) {
		sglen = mapped ? sg_dma_len(sg) : sg->length;
		if (skip > sglen) {
			skip -= sglen;
			continue;
		}

		len = min_t(size_t, size, sglen - skip);
		if (!curr->in_sg0) {
			curr->in_sg0 = sg;
			curr->skip_sg0 = skip;
		}
		size -= len;
		curr->nents++;
		curr->length_last_sg = len;

		while (!size && (skip + len < sglen) && (--nb_splits > 0)) {
			curr++;
			size = *(++sizes);
			skip += len;
			len = min_t(size_t, size, sglen - skip);

			curr->in_sg0 = sg;
			curr->skip_sg0 = skip;
			curr->nents = 1;
			curr->length_last_sg = len;
			size -= len;
		}
		skip = 0;

		if (!size && --nb_splits > 0) {
			curr++;
			size = *(++sizes);
		}

		if (!nb_splits)
			break;
	}

	return (size || !splitters[0].in_sg0) ? -EINVAL : 0;
}

static void sg_split_phys(struct sg_splitter *splitters, const int nb_splits)
{
	int i, j;
	struct scatterlist *in_sg, *out_sg;
	struct sg_splitter *split;

	for (i = 0, split = splitters; i < nb_splits; i++, split++) {
		in_sg = split->in_sg0;
		out_sg = split->out_sg;
		for (j = 0; j < split->nents; j++, out_sg++) {
			*out_sg = *in_sg;
			if (!j) {
				out_sg->offset += split->skip_sg0;
				out_sg->length -= split->skip_sg0;
			} else {
				out_sg->offset = 0;
			}
			sg_dma_address(out_sg) = 0;
			sg_dma_len(out_sg) = 0;
			in_sg = sg_next(in_sg);
		}
		out_sg[-1].length = split->length_last_sg;
		sg_mark_end(out_sg - 1);
	}
}

static void sg_split_mapped(struct sg_splitter *splitters, const int nb_splits)
{
	int i, j;
	struct scatterlist *in_sg, *out_sg;
	struct sg_splitter *split;

	for (i = 0, split = splitters; i < nb_splits; i++, split++) {
		in_sg = split->in_sg0;
		out_sg = split->out_sg;
		for (j = 0; j < split->nents; j++, out_sg++) {
			sg_dma_address(out_sg) = sg_dma_address(in_sg);
			sg_dma_len(out_sg) = sg_dma_len(in_sg);
			if (!j) {
				sg_dma_address(out_sg) += split->skip_sg0;
				sg_dma_len(out_sg) -= split->skip_sg0;
			}
			in_sg = sg_next(in_sg);
		}
		sg_dma_len(--out_sg) = split->length_last_sg;
	}
}

/**
 * sg_split - split a scatterlist into several scatterlists
 * @in: the input sg list
 * @in_mapped_nents: the result of a dma_map_sg(in, ...), or 0 if not mapped.
 * @skip: the number of bytes to skip in the input sg list
 * @nb_splits: the number of desired sg outputs
 * @split_sizes: the respective size of each output sg list in bytes
 * @out: an array where to store the allocated output sg lists
 * @out_mapped_nents: the resulting sg lists mapped number of sg entries. Might
 *                    be NULL if sglist not already mapped (in_mapped_nents = 0)
 * @gfp_mask: the allocation flag
 *
 * This function splits the input sg list into nb_splits sg lists, which are
 * allocated and stored into out.
 * The @in is split into :
 *  - @out[0], which covers bytes [@skip .. @skip + @split_sizes[0] - 1] of @in
 *  - @out[1], which covers bytes [@skip + split_sizes[0] ..
 *                                 @skip + @split_sizes[0] + @split_sizes[1] -1]
 * etc ...
 * It will be the caller's duty to kfree() out array members.
 *
 * Returns 0 upon success, or error code
 */
int sg_split(struct scatterlist *in, const int in_mapped_nents,
	     const off_t skip, const int nb_splits,
	     const size_t *split_sizes,
	     struct scatterlist **out, int *out_mapped_nents,
	     gfp_t gfp_mask)
{
	int i, ret;
	struct sg_splitter *splitters;

	splitters = kcalloc(nb_splits, sizeof(*splitters), gfp_mask);
	if (!splitters)
		return -ENOMEM;

	ret = sg_calculate_split(in, sg_nents(in), nb_splits, skip, split_sizes,
			   splitters, false);
	if (ret < 0)
		goto err;

	ret = -ENOMEM;
	for (i = 0; i < nb_splits; i++) {
		splitters[i].out_sg = kmalloc_array(splitters[i].nents,
						    sizeof(struct scatterlist),
						    gfp_mask);
		if (!splitters[i].out_sg)
			goto err;
	}

	/*
	 * The order of these 3 calls is important and should be kept.
	 */
	sg_split_phys(splitters, nb_splits);
	if (in_mapped_nents) {
		ret = sg_calculate_split(in, in_mapped_nents, nb_splits, skip,
					 split_sizes, splitters, true);
		if (ret < 0)
			goto err;
		sg_split_mapped(splitters, nb_splits);
	}

	for (i = 0; i < nb_splits; i++) {
		out[i] = splitters[i].out_sg;
		if (out_mapped_nents)
			out_mapped_nents[i] = splitters[i].nents;
	}

	kfree(splitters);
	return 0;

err:
	for (i = 0; i < nb_splits; i++)
		kfree(splitters[i].out_sg);
	kfree(splitters);
	return ret;
}
EXPORT_SYMBOL(sg_split);