block: properly wind back iovec iterator now

kernel-src/io/block/nvme.c

@@ -514,10 +514,7 @@ static int rwblocks(nvmenamespace_t *namespace, iovec_iterator_t *iovec_iterator
 	while (done < count) {
 		void *page;
 		size_t page_offset, page_remaining;
-		// XXX this takes an entire page from the iovec, though it may not be used fully.
-		// ATM this does not really matter but it could at one point in the future
 		err = iovec_iterator_next_page(iovec_iterator, &page_offset, &page_remaining, &page);
-
 		if (err)
 			break;
 
@@ -537,6 +534,13 @@ static int rwblocks(nvmenamespace_t *namespace, iovec_iterator_t *iovec_iterator
 
 		pmm_release((void *)prp[0]);
 
+		// if we didnt use the whole space in the page, set the iterator back a bit
+		size_t diff_between_available_and_used = page_remaining - docount * namespace->blocksize;
+		if (diff_between_available_and_used) {
+			size_t iterator_offset = iovec_iterator_total_offset(iovec_iterator);
+			iovec_iterator_set(iovec_iterator, iterator_offset - diff_between_available_and_used);
+		}
+
 		if (err)
 			break;
 

kernel-src/io/block/vioblk.c

@@ -135,6 +135,13 @@ static int vioblk_rw(vioblkdev_t *blkdev, iovec_iterator_t *iovec_iterator, uint
 
 		pmm_release(page);
 
+		// if we didnt use the whole space in the page, set the iterator back a bit
+		size_t diff_between_available_and_used = page_remaining - docount * 512;
+		if (diff_between_available_and_used) {
+			size_t iterator_offset = iovec_iterator_total_offset(iovec_iterator);
+			iovec_iterator_set(iovec_iterator, iterator_offset - diff_between_available_and_used);
+		}
+
 		if (*statushhdm) {
 			err = EIO;
 			break;