linux/lib/sg_split.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2015 Robert Jarzmik <[email protected]>
 *
 * Scatterlist splitting helpers.
 */

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

struct sg_splitter { … };

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)
{ … }

static void sg_split_phys(struct sg_splitter *splitters, const int nb_splits)
{ … }

static void sg_split_mapped(struct sg_splitter *splitters, const int nb_splits)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);