On 11/8/22 9:00 PM, Michał Mirosław wrote:
- @start: Starting address of the region
- @len: Length of the region (All the pages in this length are included)
- @vec: Address of page_region struct array for output
- @vec_len: Length of the page_region struct array
- @max_pages: Optional max return pages (It must be less than vec_len if specified)
I think we discussed that this is not counting the same things as vec_len, so there should not be a reference between the two. The limit is whatever fits under both conditions (IOW: n_vecs <= vec_len && (!max_pages || n_pages <= max_pages).
In worse case when pages cannot be folded into the page_region, the one page_region may have information of only one page. This is why I've compared them. I want to communicate to the user that if max_pages is used, the vec_len should be of equal or greater size (to cater worse case which can happen at any time). Otherwise in worse case, the api can return without finding the max_pages number of pages. I don't know how should I put this in the comment.
I'm not sure you need to, as this conclusion follows from the range vs page distinction. A user who wants to cater for the worst case will provide big-enough `vec` array, but another, who might be memory-constrained, could instead just retry the call with `start` updated to just after the last returned page until the ioctl() returns less ranges than `vec_len` allows.
Makes sense. I'll update and send next revision.
Thanks, Usama
Best Regards Michał Mirosław