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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next v2] tap: report IFF_DETACH_QUEUE in TUNGETIFF Date: Sun, 4 Oct 2026 23:17:38 +0530 Message-ID: <20261004174739.36179-1-umangpokhriyall@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit tun sets IFF_DETACH_QUEUE in the flags returned by TUNGETIFF when the queue is detached, since commit 3d407a80b62f ("tun: Report whether the queue is attached or not"). tap does not, so userspace cannot tell a detached macvtap or ipvtap queue from an attached one. Cloud Hypervisor ran into this when checking queue state on macvtap. Report the flag from q->enabled, as tun does. Unlike tun, tap accepts TUNSETIFF on a bound fd, so ignore IFF_DETACH_QUEUE there to keep writing the TUNGETIFF flags back working. Assisted-by: LLM Signed-off-by: Umang Pokhriyal --- Notes: v2: - ignore IFF_DETACH_QUEUE in TUNSETIFF so the TUNGETIFF flags can be written back, and describe the change as parity with tun (Sashiko) - drop Willem's Reviewed-by because of the new TUNSETIFF hunk v1: https://lore.kernel.org/netdev/20260929142238.41742-1-umangpokhriyall@gmail.com/ drivers/net/tap.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/tap.c b/drivers/net/tap.c index ff67d99deb39e..832439b8a8988 100644 --- a/drivers/net/tap.c +++ b/drivers/net/tap.c @@ -932,6 +932,9 @@ static long tap_ioctl(struct file *file, unsigned int cmd, if (get_user(u, &ifr->ifr_flags)) return -EFAULT; + /* TUNGETIFF may report IFF_DETACH_QUEUE, ignore it here */ + u &= ~IFF_DETACH_QUEUE; + ret = 0; if ((u & ~TAP_IFFEATURES) != (IFF_NO_PI | IFF_TAP)) ret = -EINVAL; @@ -950,6 +953,8 @@ static long tap_ioctl(struct file *file, unsigned int cmd, ret = 0; u = q->flags; + if (!q->enabled) + u |= IFF_DETACH_QUEUE; if (copy_to_user(&ifr->ifr_name, tap->dev->name, IFNAMSIZ) || put_user(u, &ifr->ifr_flags)) ret = -EFAULT; base-commit: cfb7793d1bc0f7d90571611979654cf1b3886b29 -- 2.53.0