test(e2e): reproduce constrained dev shm failure

Co-authored-by: GPT-5.6 <gpt-5.6@openai.com>

Author: wan9chi

Cargo.lock

@@ -31,6 +31,9 @@ vite_str = { workspace = true }
 vite_task = { workspace = true }
 which = { workspace = true }
 
+[target.'cfg(target_os = "linux")'.dependencies]
+nix = { workspace = true, features = ["mount", "sched", "user"] }
+
 [dev-dependencies]
 cow-utils = { workspace = true }
 cp_r = { workspace = true }
@@ -64,5 +67,4 @@ name = "e2e_snapshots"
 harness = false
 
 [lib]
-test = false
 doctest = false

crates/vite_task_bin/Cargo.toml

@@ -23,7 +23,9 @@ mod print_file;
 mod read_stdin;
 mod replace_file_content;
 mod rm;
+mod small_dev_shm;
 mod stat_file;
+mod stat_long_filename;
 mod touch_file;
 mod write_file;
 
@@ -32,7 +34,7 @@ fn main() {
     if args.len() < 2 {
         eprintln!("Usage: vtt <subcommand> [args...]");
         eprintln!(
-            "Subcommands: barrier, check-tty, cp, exit, exit-on-ctrlc, grep-file, list-dir, mkdir, pipe-stdin, print, print-color, print-cwd, print-env, print-file, read-stdin, replace-file-content, rm, stat-file, touch-file, write-file"
+            "Subcommands: barrier, check-tty, cp, exit, exit-on-ctrlc, grep-file, list-dir, mkdir, pipe-stdin, print, print-color, print-cwd, print-env, print-file, read-stdin, replace-file-content, rm, small_dev_shm, stat-file, stat_long_filename, touch-file, write-file"
         );
         std::process::exit(1);
     }
@@ -64,10 +66,12 @@ fn main() {
         "read-stdin" => read_stdin::run(),
         "replace-file-content" => replace_file_content::run(&args[2..]),
         "rm" => rm::run(&args[2..]),
+        "small_dev_shm" => small_dev_shm::run(&args[2..]),
         "stat-file" => {
             stat_file::run(&args[2..]);
             Ok(())
         }
+        "stat_long_filename" => stat_long_filename::run(&args[2..]),
         "touch-file" => touch_file::run(&args[2..]),
         "write-file" => write_file::run(&args[2..]),
         other => {

crates/vite_task_bin/src/vtt/main.rs

@@ -0,0 +1,116 @@
+use std::error::Error;
+
+const USAGE: &str = "Usage: vtt small_dev_shm <command> [args...]";
+
+pub fn run(args: &[String]) -> Result<(), Box<dyn Error>> {
+    let (program, command_args) = parse_command(args)?;
+    run_platform(program, command_args)?;
+    Ok(())
+}
+
+fn parse_command(args: &[String]) -> Result<(&str, &[String]), &'static str> {
+    args.split_first().map(|(program, args)| (program.as_str(), args)).ok_or(USAGE)
+}
+
+#[cfg(target_os = "linux")]
+fn write_procfs(path: &str, content: &str) -> std::io::Result<()> {
+    use std::io::Write as _;
+
+    let mut file = std::fs::OpenOptions::new().write(true).open(path)?;
+    file.write_all(content.as_bytes())
+}
+
+#[cfg(target_os = "linux")]
+fn run_platform(program: &str, command_args: &[String]) -> std::io::Result<()> {
+    use std::{os::unix::process::ExitStatusExt as _, process::Command};
+
+    use nix::{
+        mount::{MsFlags, mount},
+        sched::{CloneFlags, unshare},
+        unistd::{Gid, Uid},
+    };
+
+    fn operation_error(operation: &str, error: impl std::fmt::Display) -> std::io::Error {
+        std::io::Error::other(format!("{operation}: {error}"))
+    }
+
+    let uid = Uid::current().as_raw();
+    let gid = Gid::current().as_raw();
+
+    unshare(CloneFlags::CLONE_NEWUSER | CloneFlags::CLONE_NEWNS)
+        .map_err(|error| operation_error("unshare user and mount namespaces", error))?;
+
+    write_procfs("/proc/self/uid_map", &format!("0 {uid} 1\n"))
+        .map_err(|error| operation_error("write /proc/self/uid_map", error))?;
+    match write_procfs("/proc/self/setgroups", "deny") {
+        Ok(()) => {}
+        Err(error) if error.kind() == std::io::ErrorKind::NotFound => {}
+        Err(error) => return Err(operation_error("write /proc/self/setgroups", error)),
+    }
+    write_procfs("/proc/self/gid_map", &format!("0 {gid} 1\n"))
+        .map_err(|error| operation_error("write /proc/self/gid_map", error))?;
+
+    mount(None::<&str>, "/", None::<&str>, MsFlags::MS_REC | MsFlags::MS_PRIVATE, None::<&str>)
+        .map_err(|error| operation_error("make / recursively private", error))?;
+
+    mount(
+        Some("tmpfs"),
+        "/dev/shm",
+        Some("tmpfs"),
+        MsFlags::empty(),
+        Some("nr_blocks=1,huge=never"),
+    )
+    .map_err(|error| operation_error("mount one-page tmpfs at /dev/shm", error))?;
+
+    let status = Command::new(program).args(command_args).status()?;
+    let code = status.code().unwrap_or_else(|| status.signal().map_or(1, |signal| 128 + signal));
+    std::process::exit(code);
+}
+
+#[cfg(not(target_os = "linux"))]
+fn run_platform(_program: &str, _command_args: &[String]) -> std::io::Result<()> {
+    Err(std::io::Error::new(
+        std::io::ErrorKind::Unsupported,
+        "vtt small_dev_shm is only supported on Linux",
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn requires_a_command() {
+        assert_eq!(parse_command(&[]).unwrap_err(), USAGE);
+    }
+
+    #[test]
+    fn parses_command_and_arguments() {
+        let args = ["vt".to_owned(), "run".to_owned(), "stress".to_owned()];
+        let (program, command_args) = parse_command(&args).unwrap();
+
+        assert_eq!(program, "vt");
+        assert_eq!(command_args, ["run", "stress"]);
+    }
+
+    #[cfg(target_os = "linux")]
+    #[test]
+    fn procfs_writer_does_not_create_missing_files() {
+        let tempdir = tempfile::tempdir().unwrap();
+        let missing = tempdir.path().join("missing");
+
+        let error = write_procfs(missing.to_str().unwrap(), "content").unwrap_err();
+
+        assert_eq!(error.kind(), std::io::ErrorKind::NotFound);
+        assert!(!missing.exists());
+    }
+
+    #[cfg(not(target_os = "linux"))]
+    #[test]
+    fn reports_unsupported_platform() {
+        let error = run_platform("vt", &[]).unwrap_err();
+
+        assert_eq!(error.kind(), std::io::ErrorKind::Unsupported);
+        assert_eq!(error.to_string(), "vtt small_dev_shm is only supported on Linux");
+    }
+}

crates/vite_task_bin/src/vtt/small_dev_shm.rs

@@ -0,0 +1,123 @@
+use std::{error::Error, io};
+
+const USAGE: &str = "Usage: vtt stat_long_filename <count>";
+#[cfg(target_os = "linux")]
+const STATX_BASIC_STATS: u32 = 0x07ff;
+
+pub fn run(args: &[String]) -> Result<(), Box<dyn Error>> {
+    let count = parse_count(args)?;
+    access_generated_path(count, metadata)?;
+    Ok(())
+}
+
+fn parse_count(args: &[String]) -> Result<usize, String> {
+    let [count] = args else { return Err(USAGE.to_owned()) };
+    count.parse().map_err(|_| USAGE.to_owned())
+}
+
+fn generated_path(count: usize) -> String {
+    "x".repeat(count)
+}
+
+fn access_generated_path(
+    count: usize,
+    mut metadata: impl FnMut(&str) -> io::Result<()>,
+) -> io::Result<()> {
+    let path = generated_path(count);
+    match metadata(&path) {
+        Ok(()) => Ok(()),
+        Err(error)
+            if error.kind() == io::ErrorKind::NotFound
+                || error.raw_os_error() == Some(libc::ENAMETOOLONG) =>
+        {
+            Ok(())
+        }
+        Err(error) => Err(error),
+    }
+}
+
+#[cfg(target_os = "linux")]
+fn metadata(path: &str) -> io::Result<()> {
+    use std::{ffi::CString, mem::MaybeUninit};
+
+    let path = CString::new(path)
+        .map_err(|_| io::Error::new(io::ErrorKind::InvalidInput, "path contains NUL"))?;
+    // Linux's `struct statx` is 256 bytes and 64-bit aligned on supported targets.
+    let mut statx = MaybeUninit::<[u64; 32]>::uninit();
+    // SAFETY: `path` is NUL-terminated, `statx` points to writable storage, and
+    // all six variadic arguments use the type read by fspy's syscall interceptor.
+    let result = unsafe {
+        libc::syscall(
+            libc::SYS_statx,
+            libc::c_long::from(libc::AT_FDCWD),
+            path.as_ptr() as libc::c_long,
+            0 as libc::c_long,
+            libc::c_long::from(STATX_BASIC_STATS),
+            statx.as_mut_ptr() as libc::c_long,
+            0 as libc::c_long,
+        )
+    };
+    if result == -1 { Err(io::Error::last_os_error()) } else { Ok(()) }
+}
+
+#[cfg(not(target_os = "linux"))]
+fn metadata(path: &str) -> io::Result<()> {
+    std::fs::metadata(path).map(|_| ())
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+
+    use super::*;
+
+    fn strings(args: &[&str]) -> Vec<String> {
+        args.iter().map(|arg| (*arg).to_owned()).collect()
+    }
+
+    #[test]
+    fn parses_exactly_one_usize_count() {
+        assert_eq!(parse_count(&strings(&["1048576"])).unwrap(), 1_048_576);
+        assert_eq!(parse_count(&[]).unwrap_err(), USAGE);
+        assert_eq!(parse_count(&strings(&["1", "2"])).unwrap_err(), USAGE);
+        assert_eq!(parse_count(&strings(&["many"])).unwrap_err(), USAGE);
+    }
+
+    #[test]
+    fn generates_an_exact_relative_non_nul_ascii_path() {
+        let path = generated_path(4096);
+
+        assert_eq!(path.len(), 4096);
+        assert!(Path::new(&path).is_relative());
+        assert!(path.is_ascii());
+        assert!(!path.as_bytes().contains(&0));
+    }
+
+    #[test]
+    fn makes_one_metadata_access_and_accepts_enametoolong() {
+        let mut calls = 0;
+
+        access_generated_path(4096, |path| {
+            calls += 1;
+            assert_eq!(path.len(), 4096);
+            Err(io::Error::from_raw_os_error(libc::ENAMETOOLONG))
+        })
+        .unwrap();
+
+        assert_eq!(calls, 1);
+    }
+
+    #[test]
+    fn accepts_a_missing_path() {
+        access_generated_path(8, |_| Err(io::Error::from(io::ErrorKind::NotFound))).unwrap();
+    }
+
+    #[test]
+    fn propagates_unexpected_metadata_errors() {
+        let error =
+            access_generated_path(8, |_| Err(io::Error::from(io::ErrorKind::PermissionDenied)))
+                .unwrap_err();
+
+        assert_eq!(error.kind(), io::ErrorKind::PermissionDenied);
+    }
+}

crates/vite_task_bin/src/vtt/stat_long_filename.rs

@@ -0,0 +1 @@
+{}

crates/vite_task_bin/tests/e2e_snapshots/fixtures/constrained_dev_shm/package.json

@@ -0,0 +1,7 @@
+[[e2e]]
+name = "constrained_dev_shm"
+comment = """
+Mounting a one-page `/dev/shm` reproduces the SIGBUS seen before fspy moved its shared-memory backing to memfd.
+"""
+platform = "linux-gnu"
+steps = [["vtt", "small_dev_shm", "vt", "run", "stress"]]

crates/vite_task_bin/tests/e2e_snapshots/fixtures/constrained_dev_shm/snapshots.toml

@@ -0,0 +1,11 @@
+# constrained_dev_shm
+
+Mounting a one-page `/dev/shm` reproduces the SIGBUS seen before fspy moved its shared-memory backing to memfd.
+
+## `vtt small_dev_shm vt run stress`
+
+**Exit code:** 135
+
+```
+$ vtt stat_long_filename 1048576
+```

crates/vite_task_bin/tests/e2e_snapshots/fixtures/constrained_dev_shm/snapshots/constrained_dev_shm.md

@@ -0,0 +1,8 @@
+{
+  "tasks": {
+    "stress": {
+      "command": "vtt stat_long_filename 1048576",
+      "cache": true
+    }
+  }
+}