diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/scatterlist.c | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/lib/scatterlist.c b/lib/scatterlist.c index 6096e89bee55..e719adf695bf 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -319,6 +319,70 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask) EXPORT_SYMBOL(sg_alloc_table); /** + * sg_alloc_table_from_pages - Allocate and initialize an sg table from + * an array of pages + * @sgt: The sg table header to use + * @pages: Pointer to an array of page pointers + * @n_pages: Number of pages in the pages array + * @offset: Offset from start of the first page to the start of a buffer + * @size: Number of valid bytes in the buffer (after offset) + * @gfp_mask: GFP allocation mask + * + * Description: + * Allocate and initialize an sg table from a list of pages. Contiguous + * ranges of the pages are squashed into a single scatterlist node. A user + * may provide an offset at a start and a size of valid data in a buffer + * specified by the page array. The returned sg table is released by + * sg_free_table. + * + * Returns: + * 0 on success, negative error on failure + */ +int sg_alloc_table_from_pages(struct sg_table *sgt, + struct page **pages, unsigned int n_pages, + unsigned long offset, unsigned long size, + gfp_t gfp_mask) +{ + unsigned int chunks; + unsigned int i; + unsigned int cur_page; + int ret; + struct scatterlist *s; + + /* compute number of contiguous chunks */ + chunks = 1; + for (i = 1; i < n_pages; ++i) + if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) + ++chunks; + + ret = sg_alloc_table(sgt, chunks, gfp_mask); + if (unlikely(ret)) + return ret; + + /* merging chunks and putting them into the scatterlist */ + cur_page = 0; + for_each_sg(sgt->sgl, s, sgt->orig_nents, i) { + unsigned long chunk_size; + unsigned int j; + + /* look for the end of the current chunk */ + for (j = cur_page + 1; j < n_pages; ++j) + if (page_to_pfn(pages[j]) != + page_to_pfn(pages[j - 1]) + 1) + break; + + chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset; + sg_set_page(s, pages[cur_page], min(size, chunk_size), offset); + size -= chunk_size; + offset = 0; + cur_page = j; + } + + return 0; +} +EXPORT_SYMBOL(sg_alloc_table_from_pages); + +/** * sg_miter_start - start mapping iteration over a sg list * @miter: sg mapping iter to be started * @sgl: sg list to iterate over |