[PATCH net-next v14 1/5] tun/tap: add IFF_BACKPRESSURE flag
From: Simon Schippers <hidden>
Date: 2026-08-04 01:53:47
Also in:
kvm, linux-doc, lkml, virtualization
Subsystem:
networking drivers, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Add the IFF_BACKPRESSURE flag to the UAPI header and to its tools/ copy. The flag has no effect yet, it is the opt-in switch for the qdisc backpressure logic added by the following patches. It is added to TUN_FEATURES only in the last patch of the series, once the implementation is complete. Until then TUNSETIFF silently masks it off, as it does for any flag outside TUN_FEATURES. Keeping the flag and its users in separate patches would either leave a window where backpressure is unconditional, or make the opt-in a later add-on. Adding the flag first lets every following patch be a no-op unless it is set. Signed-off-by: Simon Schippers <redacted> --- include/uapi/linux/if_tun.h | 4 ++++ tools/include/uapi/linux/if_tun.h | 4 ++++ 2 files changed, 8 insertions(+)
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 79d53c7a1ebd..a0ddc50a7534 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h@@ -69,6 +69,10 @@ #define IFF_NAPI_FRAGS 0x0020 /* Used in TUNSETIFF to bring up tun/tap without carrier */ #define IFF_NO_CARRIER 0x0040 +/* Stop the queue instead of dropping when the internal ring is full, so an + * attached qdisc applies backpressure instead of being bypassed. + */ +#define IFF_BACKPRESSURE 0x0080 #define IFF_NO_PI 0x1000 /* This flag has no real effect */ #define IFF_ONE_QUEUE 0x2000
diff --git a/tools/include/uapi/linux/if_tun.h b/tools/include/uapi/linux/if_tun.h
index 2ec07de1d73b..2c85525704c1 100644
--- a/tools/include/uapi/linux/if_tun.h
+++ b/tools/include/uapi/linux/if_tun.h@@ -67,6 +67,10 @@ #define IFF_TAP 0x0002 #define IFF_NAPI 0x0010 #define IFF_NAPI_FRAGS 0x0020 +/* Stop the queue instead of dropping when the internal ring is full, so an + * attached qdisc applies backpressure instead of being bypassed. + */ +#define IFF_BACKPRESSURE 0x0080 #define IFF_NO_PI 0x1000 /* This flag has no real effect */ #define IFF_ONE_QUEUE 0x2000
--
2.43.0