main: Enable the api-socket to be passed as an fd

To avoid race issues where the api-socket may not be created by the
time a cloud-hypervisor caller is ready to look for it, enable the
caller to pass the api-socket fd directly.

Avoid breaking current callers by allowing the --api-socket path to be
passed as it is now in addition to through the path argument.

Signed-off-by: William Douglas <william.r.douglas@gmail.com>

src/main.rs

@@ -25,7 +25,7 @@ use signal_hook::{
 };
 use std::env;
 use std::fs::File;
-use std::os::unix::io::FromRawFd;
+use std::os::unix::io::{FromRawFd, RawFd};
 use std::sync::mpsc::channel;
 use std::sync::{Arc, Mutex};
 use std::thread;
@@ -62,6 +62,8 @@ enum Error {
     ThreadJoin(std::boxed::Box<dyn std::any::Any + std::marker::Send>),
     #[error("VMM thread exited with error: {0}")]
     VmmThread(#[source] vmm::Error),
+    #[error("Error parsing --api-socket: {0}")]
+    ParsingApiSocket(std::num::ParseIntError),
     #[error("Error parsing --event-monitor: {0}")]
     ParsingEventMonitor(option_parser::OptionParserError),
     #[error("Error parsing --event-monitor: path or fd required")]
@@ -324,7 +326,7 @@ fn create_app<'a, 'b>(
         .arg(
             Arg::with_name("api-socket")
                 .long("api-socket")
-                .help("HTTP API socket path (UNIX domain socket).")
+                .help("HTTP API socket (UNIX domain socket): path=</path/to/a/file> or fd=<fd>.")
                 .takes_value(true)
                 .min_values(1)
                 .group("vmm-config"),
@@ -379,7 +381,7 @@ fn create_app<'a, 'b>(
     app
 }
 
-fn start_vmm(cmd_arguments: ArgMatches, api_socket_path: &Option<String>) -> Result<(), Error> {
+fn start_vmm(cmd_arguments: ArgMatches) -> Result<Option<String>, Error> {
     let log_level = match cmd_arguments.occurrences_of("v") {
         0 => LevelFilter::Warn,
         1 => LevelFilter::Info,
@@ -402,6 +404,29 @@ fn start_vmm(cmd_arguments: ArgMatches, api_socket_path: &Option<String>) -> Res
     .map(|()| log::set_max_level(log_level))
     .map_err(Error::LoggerSetup)?;
 
+    let (api_socket_path, api_socket_fd) =
+        if let Some(socket_config) = cmd_arguments.value_of("api-socket") {
+            let mut parser = OptionParser::new();
+            parser.add("path").add("fd");
+            parser.parse(socket_config).unwrap_or_default();
+
+            if let Some(fd) = parser.get("fd") {
+                (
+                    None,
+                    Some(fd.parse::<RawFd>().map_err(Error::ParsingApiSocket)?),
+                )
+            } else if let Some(path) = parser.get("path") {
+                (Some(path), None)
+            } else {
+                (
+                    cmd_arguments.value_of("api-socket").map(|s| s.to_string()),
+                    None,
+                )
+            }
+        } else {
+            (None, None)
+        };
+
     if let Some(monitor_config) = cmd_arguments.value_of("event-monitor") {
         let mut parser = OptionParser::new();
         parser.add("path").add("fd");
@@ -474,7 +499,8 @@ fn start_vmm(cmd_arguments: ArgMatches, api_socket_path: &Option<String>) -> Res
     let hypervisor = hypervisor::new().map_err(Error::CreateHypervisor)?;
     let vmm_thread = vmm::start_vmm_thread(
         env!("CARGO_PKG_VERSION").to_string(),
-        api_socket_path,
+        &api_socket_path,
+        api_socket_fd,
         api_evt.try_clone().unwrap(),
         http_sender,
         api_request_receiver,
@@ -510,7 +536,9 @@ fn start_vmm(cmd_arguments: ArgMatches, api_socket_path: &Option<String>) -> Res
     vmm_thread
         .join()
         .map_err(Error::ThreadJoin)?
-        .map_err(Error::VmmThread)
+        .map_err(Error::VmmThread)?;
+
+    Ok(api_socket_path)
 }
 
 fn main() {
@@ -519,16 +547,17 @@ fn main() {
 
     let (default_vcpus, default_memory, default_rng) = prepare_default_values();
     let cmd_arguments = create_app(&default_vcpus, &default_memory, &default_rng).get_matches();
-    let api_socket_path = cmd_arguments.value_of("api-socket").map(|s| s.to_string());
-
-    let exit_code = if let Err(e) = start_vmm(cmd_arguments, &api_socket_path) {
-        eprintln!("{}", e);
-        1
-    } else {
-        0
+    let exit_code = match start_vmm(cmd_arguments) {
+        Ok(path) => {
+            path.map(|s| std::fs::remove_file(s).ok());
+            0
+        }
+        Err(e) => {
+            eprintln!("{}", e);
+            1
+        }
     };
 
-    api_socket_path.map(|s| std::fs::remove_file(s).ok());
     std::process::exit(exit_code);
 }