[PATCH 2/5] io_uring/zcrx: notify user on frag copy fallback

Clément Léger
2026-04-22T11:29:30Z

Add a ZCRX_NOTIF_COPY notification type to signal userspace when a
received fragment could not be delivered using zero-copy and was
instead copied into a buffer.

Signed-off-by: Clément Léger <cleger@meta.com>
---
include/uapi/linux/io_uring/zcrx.h | 1 +
io_uring/zcrx.c | 7 ++++++-
io_uring/zcrx.h | 3 ++-
3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/io_uring/zcrx.h b/include/uapi/linux/io_uring/zcrx.h
index b8596d7d47b6..e0c0079626c8 100644
--- a/include/uapi/linux/io_uring/zcrx.h
+++ b/include/uapi/linux/io_uring/zcrx.h
@@ -70,6 +70,7 @@ enum zcrx_features {

enum zcrx_notification_type {
ZCRX_NOTIF_NO_BUFFERS = 1 << 0,
+ ZCRX_NOTIF_COPY = 1 << 1
};

struct zcrx_notification_desc {
diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 35ca28cb6583..732e585aa13a 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -1510,8 +1510,13 @@ static int io_zcrx_copy_frag(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
const skb_frag_t *frag, int off, int len)
{
struct page *page = skb_frag_page(frag);
+ int ret;
+
+ ret = io_zcrx_copy_chunk(req, ifq, page, off + skb_frag_off(frag), len);
+ if (ret > 0)
+ zcrx_send_notif(ifq, ZCRX_NOTIF_COPY);

- return io_zcrx_copy_chunk(req, ifq, page, off + skb_frag_off(frag), len);
+ return ret;
}

static int io_zcrx_recv_frag(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
diff --git a/io_uring/zcrx.h b/io_uring/zcrx.h
index 3ddebed06d57..1bd63adaa711 100644
--- a/io_uring/zcrx.h
+++ b/io_uring/zcrx.h
@@ -11,7 +11,8 @@
#define ZCRX_SUPPORTED_REG_FLAGS (ZCRX_REG_IMPORT | ZCRX_REG_NODEV)
#define ZCRX_FEATURES (ZCRX_FEATURE_RX_PAGE_SIZE |\
ZCRX_FEATURE_NOTIFICATION)
-#define ZCRX_NOTIF_TYPE_MASK (ZCRX_NOTIF_NO_BUFFERS)
+#define ZCRX_NOTIF_TYPE_MASK (ZCRX_NOTIF_NO_BUFFERS |\
+ ZCRX_NOTIF_COPY)

struct io_zcrx_mem {
unsigned long size;
--
2.52.0