[RFC PATCH v2 05/13] io_uring: create page freelist for the ifq region

[Jonathan Lemon <jonathan.lemon@gmail.com>]

Create a freelist where the driver can obtain pages for the packet
backing store.  Use the page's page_private field to record lookup
information.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
---
 io_uring/zctap.c | 61 ++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 56 insertions(+), 5 deletions(-)

diff --git a/io_uring/zctap.c b/io_uring/zctap.c
index f8a5702f93f4..af2e871b1b62 100644
--- a/io_uring/zctap.c
+++ b/io_uring/zctap.c
@@ -27,18 +27,68 @@ struct ifq_region {
 
 typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf *bpf);
 
+static void zctap_set_page_info(struct page *page, u64 info)
+{
+	set_page_private(page, info);
+}
+
+static u64 zctap_mk_page_info(u16 region_id, u16 pgid)
+{
+	return (u64)0xface << 48 | (u64)region_id << 16 | (u64)pgid;
+}
+
 static void io_remove_ifq_region(struct ifq_region *ifr)
 {
+	struct io_mapped_ubuf *imu;
+	struct page *page;
+	int i;
+
+	imu = ifr->imu;
+	for (i = 0; i < ifr->nr_pages; i++) {
+		page = imu->bvec[i].bv_page;
+
+		ClearPagePrivate(page);
+		set_page_private(page, 0);
+	}
+
 	kvfree(ifr);
 }
 
+static int io_zctap_map_region(struct ifq_region *ifr)
+{
+	struct io_mapped_ubuf *imu;
+	struct page *page;
+	u64 info;
+	int i;
+
+	imu = ifr->imu;
+	for (i = 0; i < ifr->nr_pages; i++) {
+		page = imu->bvec[i].bv_page;
+		if (PagePrivate(page))
+			goto out;
+		SetPagePrivate(page);
+		info = zctap_mk_page_info(ifr->id, i);
+		zctap_set_page_info(page, info);
+		ifr->freelist[i] = page;
+	}
+	return 0;
+
+out:
+	while (i--) {
+		page = imu->bvec[i].bv_page;
+		ClearPagePrivate(page);
+		set_page_private(page, 0);
+	}
+	return -EEXIST;
+}
+
 int io_provide_ifq_region(struct io_zctap_ifq *ifq, u16 id)
 {
 	struct io_ring_ctx *ctx = ifq->ctx;
 	struct io_mapped_ubuf *imu;
 	struct ifq_region *ifr;
-	int i, nr_pages;
-	struct page *page;
+	int nr_pages;
+	int err;
 
 	/* XXX for now, only allow one region per ifq. */
 	if (ifq->region)
@@ -63,9 +113,10 @@ int io_provide_ifq_region(struct io_zctap_ifq *ifq, u16 id)
 	ifr->count = nr_pages;
 	ifr->id = id;
 
-	for (i = 0; i < nr_pages; i++) {
-		page = imu->bvec[i].bv_page;
-		ifr->freelist[i] = page;
+	err = io_zctap_map_region(ifr);
+	if (err) {
+		kvfree(ifr);
+		return err;
 	}
 
 	ifq->region = ifr;
-- 
2.30.2