tun/tap: add IFF_BACKPRESSURE flag

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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 <simon.schippers@tu-dortmund.de>
Link: https://patch.msgid.link/20260803183641.96882-2-simon.schippers@tu-dortmund.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Simon Schippers 2026-08-03 20:36:37 +02:00 • committed by Jakub Kicinski

parent d4e359b360

commit 485e38995c

2 changed files with 8 additions and 0 deletions

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4

include/uapi/linux/if_tun.h

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4

tools/include/uapi/linux/if_tun.h

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