Re: [v2,4/7] scatterlist: add sg_alloc_table_from_buf() helper

Vignesh R
2016-03-31T04:58:30Z

Hi,

On 03/30/2016 09:09 PM, Boris BREZILLON wrote:

[...]

> +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t len,
> + const struct sg_constraints *constraints,
> + gfp_t gfp_mask)
> +{
> + struct sg_constraints cons = { };
> + size_t remaining, chunk_len;
> + const void *sg_buf;
> + int i, ret;
> +
> + if (constraints)
> + cons = *constraints;
> +
> + ret = sg_check_constraints(&cons, buf, len);
> + if (ret)
> + return ret;
> +
> + sg_buf = buf;
> + remaining = len;
> + i = 0;
> + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons)
> + i++;
> +
> + ret = sg_alloc_table(sgt, i, gfp_mask);
> + if (ret)
> + return ret;
> +
> + sg_buf = buf;
> + remaining = len;
> + i = 0;
> + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) {
> + if (is_vmalloc_addr(sg_buf)) {
> + struct page *vm_page;
> +
> + vm_page = vmalloc_to_page(sg_buf);
> + if (!vm_page) {
> + ret = -ENOMEM;
> + goto err_free_table;
> + }
> +
> + sg_set_page(&sgt->sgl[i], vm_page, chunk_len,
> + offset_in_page(sg_buf));
> + } else {
> + sg_set_buf(&sgt->sgl[i], sg_buf, chunk_len);
> + }
> +

If the buf address is in PKMAP_BASE - PAGE_OFFSET-1 region (I have
observed that JFFS2 FS provides buffers in above region to MTD layer),
if CONFIG_DEBUG_SG is set then sg_set_buf() will throw a BUG_ON() as
virt_addr_is_valid() will return false. Is there a sane way to handle
buffers of PKMAP_BASE region with sg_* APIs?
Or, is the function sg_alloc_table_from_buf() not to be used with such
buffers?

--
Regards
Vignesh