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/*
* Copyright (C) 2015 Robert Jarzmik <robert.jarzmik@free.fr>
*
* Scatterlist splitting helpers.
*
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
*/
#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);
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);
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