Baolin Wang <baolin.wang@xxxxxxxxxx> writes:
> @@ -212,6 +212,37 @@ static inline void sg_unmark_end(struct scatterlist *sg)
> }
>
> /**
> + * sg_is_contiguous - Check if the scatterlists are contiguous
> + * @sga: SG entry
> + * @sgb: SG entry
> + *
> + * Description:
> + * If the sga scatterlist is contiguous with the sgb scatterlist,
> + * that means they can be merged together.
> + *
> + **/
> +static inline bool sg_is_contiguous(struct scatterlist *sga,
> + struct scatterlist *sgb)
> +{
> + return ((sga->page_link & ~0x3UL) + sga->offset + sga->length ==
> + (sgb->page_link & ~0x3UL));
> +}
I don't understand that one.
sga->page_link is a pointer to a "struct page *". How can it be added to an
offset within a page ???
> @@ -370,6 +370,65 @@ int sg_alloc_table(struct sg_table *table, unsigned int
> nents, gfp_t gfp_mask)
...
> /**
> + * sg_add_sg_to_table - Add one scatterlist into sg table
> + * @sgt: The sg table header to use
> + * @src: The sg need to be added into sg table
> + *
> + * Description:
> + * The 'nents' member indicates how many scatterlists added in the sg table.
> + * Copy the @src@ scatterlist into sg table and increase 'nents' member.
> + *
> + **/
> +int sg_add_sg_to_table(struct sg_table *sgt, struct scatterlist *src)
> +{
> + unsigned int i = 0, orig_nents = sgt->orig_nents;
> + struct scatterlist *sgl = sgt->sgl;
> + struct scatterlist *sg;
> +
> + /* Check if there are enough space for the new sg to be added */
> + if (sgt->nents >= sgt->orig_nents)
> + return -EINVAL;
I must admit I don't understand that one either : how do comparing the number of
"mapped" entries against the number of "allocated" entries determines if there
is enough room ?
> +/**
> + * sg_alloc_empty_table - Allocate one empty sg table
> + * @sgt: The sg table header to use
> + * @nents: Number of entries in sg list
> + * @gfp_mask: GFP allocation mask
> + *
> + * Description:
> + * Allocate and initialize an sg table. The 'nents' member of sg_table
> + * indicates how many scatterlists added in the sg table. It should set
> + * 0 which means there are no scatterlists added in this sg table now.
> + *
> + **/
> +int sg_alloc_empty_table(struct sg_table *sgt, unsigned int nents,
> + gfp_t gfp_mask)
As for this one, there has to be a purpose for it I fail to see. From far away
it looks exactly like sg_alloc_table(), excepting it "works around" the nents >
0 protection of __sg_alloc_table().
What is exactly the need for this one, and if it's usefull why not simply
changing the __sg_alloc_table() "nents > 0" test and see what the outcome of the
review will be ?
Cheers.
--
Robert
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