From 485e38995cc3b39f1aa91c1d340cc66affcea39a Mon Sep 17 00:00:00 2001 From: Simon Schippers Date: Mon, 3 Aug 2026 20:36:37 +0200 Subject: tun/tap: add IFF_BACKPRESSURE flag 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 Link: https://patch.msgid.link/20260803183641.96882-2-simon.schippers@tu-dortmund.de Signed-off-by: Jakub Kicinski --- include/uapi/linux/if_tun.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/uapi/linux') 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 -- cgit v1.2.3