From c82d6556f226572e925c0049dab5fa8e3693c830 Mon Sep 17 00:00:00 2001
From: Val Packett <val@invisiblethingslab.com>
Date: Thu, 7 May 2026 05:51:45 -0300
Subject: [PATCH] muvm: Add a --passt-args argument to pass args to passt

Sometimes it's necessary to pass additional args (such as the network
interface) to passt. It's already been possible to spawn passt externally
and give muvm its socket, but that's inconvenient especially when one
wants to keep using the nicer muvm syntax for the exposed ports.

Signed-off-by: Val Packett <val@invisiblethingslab.com>
---
 Cargo.lock                     |  7 +++++++
 crates/muvm/Cargo.toml         |  1 +
 crates/muvm/src/bin/muvm.rs    |  2 +-
 crates/muvm/src/cli_options.rs | 11 +++++++++++
 crates/muvm/src/net.rs         |  5 ++++-
 5 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index f1d1f12a..784506bc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -576,6 +576,7 @@ dependencies = [
  "rustix 0.38.34",
  "serde",
  "serde_json",
+ "shell-words",
  "tempfile",
  "tokio",
  "tokio-stream",
@@ -897,6 +898,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "shell-words"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc6fe69c597f9c37bfeeeeeb33da3530379845f10be461a66d16d03eca2ded77"
+
 [[package]]
 name = "shlex"
 version = "1.3.0"
diff --git a/crates/muvm/Cargo.toml b/crates/muvm/Cargo.toml
index f011bca8..60a1d733 100644
--- a/crates/muvm/Cargo.toml
+++ b/crates/muvm/Cargo.toml
@@ -24,6 +24,7 @@ procfs = { version = "0.18.0", default-features = false, features = [] }
 rustix = { version = "0.38.34", default-features = false, features = ["fs", "mount", "process", "pty", "std", "stdio", "system", "termios", "use-libc-auxv"] }
 serde = { version = "1.0.203", default-features = false, features = ["derive"] }
 serde_json = { version = "1.0.117", default-features = false, features = ["std"] }
+shell-words = { version = "1.1.1", default-features = false, features = ["std"] }
 tempfile = { version = "3.10.1", default-features = false, features = [] }
 tokio = { version = "1.38.0", default-features = false, features = ["io-util", "macros", "net", "process", "rt-multi-thread", "sync"] }
 tokio-stream = { version = "0.1.15", default-features = false, features = ["net", "sync"] }
diff --git a/crates/muvm/src/bin/muvm.rs b/crates/muvm/src/bin/muvm.rs
index 0827e8db..1c9fe28d 100644
--- a/crates/muvm/src/bin/muvm.rs
+++ b/crates/muvm/src/bin/muvm.rs
@@ -278,7 +278,7 @@ fn main() -> Result<ExitCode> {
                 .context("Failed to connect to `passt`")?
                 .into()
         } else {
-            start_passt(&options.publish_ports)
+            start_passt(&options.publish_ports, &options.passt_args)
                 .context("Failed to start `passt`")?
                 .into()
         };
diff --git a/crates/muvm/src/cli_options.rs b/crates/muvm/src/cli_options.rs
index 5080c911..fc3ccf74 100644
--- a/crates/muvm/src/cli_options.rs
+++ b/crates/muvm/src/cli_options.rs
@@ -37,6 +37,7 @@ pub struct Options {
     pub mem: Option<MiB>,
     pub vram: Option<MiB>,
     pub passt_socket: Option<PathBuf>,
+    pub passt_args: Vec<String>,
     pub fex_images: Vec<String>,
     pub merged_rootfs: bool,
     pub interactive: bool,
@@ -135,6 +136,15 @@ pub fn options() -> OptionParser<Options> {
         .help("Instead of starting passt, connect to passt socket at PATH")
         .argument("PATH")
         .optional();
+    let passt_args = long("passt-args")
+        .help(
+            "When starting passt, append the given arguments.
+            May contain shell-quoted args, like so: --passt-args '-l \"my log file.txt\"'",
+        )
+        .argument::<String>("ARGS")
+        .parse(|s| shell_words::split(&s))
+        .many()
+        .map(|nested| nested.into_iter().flatten().collect());
     let interactive = long("interactive")
         .short('i')
         .help("Attach to the command's stdin/out after starting it")
@@ -192,6 +202,7 @@ pub fn options() -> OptionParser<Options> {
         mem,
         vram,
         passt_socket,
+        passt_args,
         fex_images,
         merged_rootfs,
         interactive,
diff --git a/crates/muvm/src/net.rs b/crates/muvm/src/net.rs
index 8543e1c1..bc6323d4 100644
--- a/crates/muvm/src/net.rs
+++ b/crates/muvm/src/net.rs
@@ -82,7 +82,7 @@ where
     Ok(UnixStream::connect(passt_socket_path)?)
 }
 
-pub fn start_passt(publish_ports: &[String]) -> Result<UnixStream> {
+pub fn start_passt(publish_ports: &[String], passt_args: &[String]) -> Result<UnixStream> {
     // SAFETY: The child process should not inherit the file descriptor of
     // `parent_socket`. There is no documented guarantee of this, but the
     // implementation as of writing atomically sets `SOCK_CLOEXEC`.
@@ -112,6 +112,9 @@ pub fn start_passt(publish_ports: &[String]) -> Result<UnixStream> {
     for spec in publish_ports {
         cmd.args(PublishSpec::parse(spec)?.to_args());
     }
+    for arg in passt_args {
+        cmd.arg(arg);
+    }
     let child = cmd.spawn();
     if let Err(err) = child {
         return Err(err).context("Failed to execute `passt` as child process");