Add tun_ring_unconsume() and tap_ring_unconsume() wrappers to allow
external modules (e.g. vhost-net) to return previously consumed entries
back to the ring. This complements tun_ring_consume_batched() and
tap_ring_consume_batched() and enables proper error handling when
consumed packets need to be rolled back.

The functions delegate to ptr_ring_unconsume() and take a destroy
callback for entries that cannot be returned to the ring.

Co-developed-by: Tim Gebauer <tim.gebauer@tu-dortmund.de>
Signed-off-by: Tim Gebauer <tim.gebauer@tu-dortmund.de>
Co-developed by: Jon Kohler <jon@nutanix.com>
Signed-off-by: Jon Kohler <jon@nutanix.com>
Signed-off-by: Simon Schippers <simon.schippers@tu-dortmund.de>
---
 drivers/net/tap.c      | 10 ++++++++++
 drivers/net/tun.c      | 10 ++++++++++
 include/linux/if_tap.h |  4 ++++
 include/linux/if_tun.h |  5 +++++
 4 files changed, 29 insertions(+)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 01717c8fd284..0069e2f177f4 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -837,6 +837,16 @@ int tap_ring_consume_batched(struct file *file, void **array, int n)
 }
 EXPORT_SYMBOL_GPL(tap_ring_consume_batched);
 
+void tap_ring_unconsume(struct file *file, void **batch, int n,
+			void (*destroy)(void *))
+{
+	struct tap_queue *q = file->private_data;
+	struct ptr_ring *ring = &q->ring;
+
+	ptr_ring_unconsume(ring, batch, n, destroy);
+}
+EXPORT_SYMBOL_GPL(tap_ring_unconsume);
+
 static ssize_t tap_do_read(struct tap_queue *q,
 			   struct iov_iter *to,
 			   int noblock, struct sk_buff *skb)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 42df185341ad..bf109440d2c7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3837,6 +3837,16 @@ int tun_ring_consume_batched(struct file *file, void **array, int n)
 }
 EXPORT_SYMBOL_GPL(tun_ring_consume_batched);
 
+void tun_ring_unconsume(struct file *file, void **batch, int n,
+			void (*destroy)(void *))
+{
+	struct tun_file *tfile = file->private_data;
+	struct ptr_ring *ring = &tfile->tx_ring;
+
+	ptr_ring_unconsume(ring, batch, n, destroy);
+}
+EXPORT_SYMBOL_GPL(tun_ring_unconsume);
+
 struct ptr_ring *tun_get_tx_ring(struct file *file)
 {
 	struct tun_file *tfile;
diff --git a/include/linux/if_tap.h b/include/linux/if_tap.h
index cf8b90320b8d..28326a69745a 100644
--- a/include/linux/if_tap.h
+++ b/include/linux/if_tap.h
@@ -12,6 +12,8 @@ struct socket;
 struct socket *tap_get_socket(struct file *);
 struct ptr_ring *tap_get_ptr_ring(struct file *file);
 int tap_ring_consume_batched(struct file *file, void **array, int n);
+void tap_ring_unconsume(struct file *file, void **batch, int n,
+			void (*destroy)(void *));
 #else
 #include <linux/err.h>
 #include <linux/errno.h>
@@ -28,6 +30,8 @@ static inline int tap_ring_consume_batched(struct file *f,
 {
 	return 0;
 }
+static inline void tap_ring_unconsume(struct file *file, void **batch,
+				      int n, void (*destroy)(void *)) {}
 #endif /* CONFIG_TAP */
 
 /*
diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
index 444dda75a372..1274c6b34eb6 100644
--- a/include/linux/if_tun.h
+++ b/include/linux/if_tun.h
@@ -23,6 +23,8 @@ struct tun_msg_ctl {
 struct socket *tun_get_socket(struct file *);
 struct ptr_ring *tun_get_tx_ring(struct file *file);
 int tun_ring_consume_batched(struct file *file, void **array, int n);
+void tun_ring_unconsume(struct file *file, void **batch, int n,
+			void (*destroy)(void *));
 
 static inline bool tun_is_xdp_frame(void *ptr)
 {
@@ -62,6 +64,9 @@ static inline int tun_ring_consume_batched(struct file *file,
 	return 0;
 }
 
+static inline void tun_ring_unconsume(struct file *file, void **batch,
+				      int n, void (*destroy)(void *)) {}
+
 static inline bool tun_is_xdp_frame(void *ptr)
 {
 	return false;
-- 
2.43.0