DHCP snooper: use coarse time to avoid clock_gettime() overhead

Cargo.lock

@@ -401,6 +401,17 @@ version = "0.7.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f46ad14479a25103f283c0f10005961cf086d8dc42205bb44c46ac563475dca6"
 
+[[package]]
+name = "coarsetime"
+version = "0.1.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e58eb270476aa4fc7843849f8a35063e8743b4dbcdf6dd0f8ea0886980c204c2"
+dependencies = [
+ "libc",
+ "wasix",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "colorchoice"
 version = "1.0.2"
@@ -2296,6 +2307,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "clap",
+ "coarsetime",
  "dhcproto",
  "ip_network",
  "ipnet",
@@ -2853,6 +2865,15 @@ dependencies = [
  "wit-bindgen-rt",
 ]
 
+[[package]]
+name = "wasix"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1757e0d1f8456693c7e5c6c629bdb54884e032aa0bb53c155f6a39f94440d332"
+dependencies = [
+ "wasi 0.11.0+wasi-snapshot-preview1",
+]
+
 [[package]]
 name = "wasm-bindgen"
 version = "0.2.106"

Cargo.toml

@@ -33,6 +33,7 @@ ipnet = "2"
 oslog = "0.2.0"
 log = "0.4.29"
 serial_test = "3"
+coarsetime = "0.1.37"
 
 [profile.release]
 debug = true

lib/dhcp_snooper.rs

@@ -2,7 +2,7 @@ use dhcproto::Decodable;
 use dhcproto::v4::{DhcpOption, MessageType, OptionCode};
 use smoltcp::wire::Ipv4Address;
 use std::collections::HashSet;
-use std::time::{Duration, Instant};
+use std::time::Duration;
 
 #[derive(Default)]
 pub struct DhcpSnooper {
@@ -66,7 +66,7 @@ impl DhcpSnooper {
 #[derive(Debug)]
 pub struct Lease {
     address: Ipv4Address,
-    valid_until: Instant,
+    valid_until: coarsetime::Instant,
     dns_ips: HashSet<Ipv4Address>,
 }
 
@@ -74,7 +74,7 @@ impl Lease {
     pub fn new(address: Ipv4Address, lease_time: Duration, dns_ips: HashSet<Ipv4Address>) -> Lease {
         Lease {
             address,
-            valid_until: Instant::now() + lease_time,
+            valid_until: coarsetime::Instant::recent() + lease_time.into(),
             dns_ips,
         }
     }
@@ -84,7 +84,7 @@ impl Lease {
     }
 
     pub fn valid(&self) -> bool {
-        Instant::now() < self.valid_until
+        coarsetime::Instant::recent() < self.valid_until
     }
 
     pub fn valid_ip_source(&self, address: Ipv4Address) -> bool {

lib/proxy/mod.rs

@@ -90,6 +90,9 @@ impl Proxy<'_> {
         self.poller.arm()?;
 
         loop {
+            // Update coarse time for the DHCP snooper
+            coarsetime::Instant::update();
+
             let (vm_readable, host_readable, interrupt) = self.poller.wait()?;
 
             if vm_readable {