aya: add netlink_clsact_qdisc_exists function

This function is used to check if the clasct qdisc exists on a given interface.
This check should be performed before adding the mentioned qdisc.

aya/src/programs/tc.rs

@@ -14,8 +14,8 @@ use crate::{
     },
     programs::{define_link_wrapper, load_program, Link, ProgramData, ProgramError},
     sys::{
-        netlink_find_filter_with_name, netlink_qdisc_add_clsact, netlink_qdisc_attach,
+        netlink_clsact_qdisc_exists, netlink_find_filter_with_name, netlink_qdisc_add_clsact,
-        netlink_qdisc_detach,
+        netlink_qdisc_attach, netlink_qdisc_detach,
     },
     util::{ifindex_from_ifname, tc_handler_make},
     VerifierLogLevel,
@@ -314,6 +314,12 @@ pub fn qdisc_add_clsact(if_name: &str) -> Result<(), io::Error> {
     unsafe { netlink_qdisc_add_clsact(if_index as i32) }
 }
 
+/// Check if the `clasct` qdisc exists on the given interface.
+pub fn clsact_qdisc_exists(if_name: &str) -> Result<bool, io::Error> {
+    let if_index = ifindex_from_ifname(if_name)?;
+    unsafe { netlink_clsact_qdisc_exists(if_index as i32) }
+}
+
 /// Detaches the programs with the given name.
 ///
 /// # Errors

aya/src/sys/netlink.rs

@@ -1,12 +1,19 @@
-use std::{collections::HashMap, ffi::CStr, io, mem, os::fd::RawFd, ptr, slice};
+use std::{
+    collections::HashMap,
+    ffi::CStr,
+    io,
+    mem::{self},
+    os::fd::RawFd,
+    ptr, slice,
+};
 use thiserror::Error;
 
 use libc::{
     close, getsockname, nlattr, nlmsgerr, nlmsghdr, recv, send, setsockopt, sockaddr_nl, socket,
     AF_NETLINK, AF_UNSPEC, ETH_P_ALL, IFF_UP, IFLA_XDP, NETLINK_EXT_ACK, NETLINK_ROUTE,
     NLA_ALIGNTO, NLA_F_NESTED, NLA_TYPE_MASK, NLMSG_DONE, NLMSG_ERROR, NLM_F_ACK, NLM_F_CREATE,
-    NLM_F_DUMP, NLM_F_ECHO, NLM_F_EXCL, NLM_F_MULTI, NLM_F_REQUEST, RTM_DELTFILTER, RTM_GETTFILTER,
+    NLM_F_DUMP, NLM_F_ECHO, NLM_F_EXCL, NLM_F_MULTI, NLM_F_REQUEST, RTM_DELTFILTER, RTM_GETQDISC,
-    RTM_NEWQDISC, RTM_NEWTFILTER, RTM_SETLINK, SOCK_RAW, SOL_NETLINK,
+    RTM_GETTFILTER, RTM_NEWQDISC, RTM_NEWTFILTER, RTM_SETLINK, SOCK_RAW, SOL_NETLINK,
 };
 
 use crate::{
@@ -68,6 +75,46 @@ pub(crate) unsafe fn netlink_set_xdp_fd(
     Ok(())
 }
 
+pub(crate) unsafe fn netlink_clsact_qdisc_exists(if_index: i32) -> Result<bool, io::Error> {
+    let sock = NetlinkSocket::open()?;
+
+    let mut req = mem::zeroed::<TcRequest>();
+
+    let nlmsg_len = mem::size_of::<nlmsghdr>() + mem::size_of::<tcmsg>();
+
+    req.header = nlmsghdr {
+        nlmsg_len: nlmsg_len as u32,
+        nlmsg_flags: (NLM_F_REQUEST | NLM_F_ACK | NLM_F_DUMP) as u16,
+        nlmsg_type: RTM_GETQDISC,
+        nlmsg_pid: 0,
+        nlmsg_seq: 1,
+    };
+    req.tc_info.tcm_family = AF_UNSPEC as u8;
+
+    sock.send(&bytes_of(&req)[..req.header.nlmsg_len as usize])?;
+
+    for msg in sock.recv()? {
+        if msg.header.nlmsg_type != RTM_NEWQDISC {
+            continue;
+        }
+
+        let tc_msg = ptr::read_unaligned(msg.data.as_ptr() as *const tcmsg);
+        if tc_msg.tcm_ifindex != if_index {
+            continue;
+        }
+
+        let attrs = parse_attrs(&msg.data[mem::size_of::<tcmsg>()..])?;
+
+        if let Some(opts) = attrs.get(&(TCA_KIND as u16)) {
+            if opts.data == b"clsact\0" {
+                return Ok(true);
+            }
+        }
+    }
+
+    Ok(false)
+}
+
 pub(crate) unsafe fn netlink_qdisc_add_clsact(if_index: i32) -> Result<(), io::Error> {
     let sock = NetlinkSocket::open()?;
 

test/integration-test/src/tests/load.rs

@@ -5,7 +5,7 @@ use aya::{
     programs::{
         links::{FdLink, PinnedLink},
         loaded_links, loaded_programs,
-        tc::qdisc_add_clsact,
+        tc::{clsact_qdisc_exists, qdisc_add_clsact},
         KProbe, SchedClassifier, TcAttachType, TracePoint, UProbe, Xdp, XdpFlags,
     },
     util::KernelVersion,
@@ -17,7 +17,10 @@ const RETRY_DURATION: time::Duration = time::Duration::from_millis(10);
 
 #[test]
 fn tc_name_limit() {
-    let _ = qdisc_add_clsact("lo");
+    let clsact_exists = clsact_qdisc_exists("lo").unwrap();
+    if !clsact_exists {
+        qdisc_add_clsact("lo").unwrap();
+    }
 
     let mut bpf = Bpf::load(crate::TC_NAME_LIMIT_TEST).unwrap();