Add file path mapping for FileTransfer

Match by longest prefix to get host paths from guest ones

sidebus-broker/src/main.rs

@@ -4,6 +4,7 @@ mod vsock;
 
 use bus::SharedHostedBus;
 use clap::Parser;
+use eyre::OptionExt;
 use futures::{TryFutureExt, stream::FuturesUnordered};
 use std::{path::PathBuf, sync::Arc, time::Duration};
 use tokio::{net::UnixListener, process::Command, sync::Mutex};
@@ -36,6 +37,10 @@ struct BrokerCli {
     #[clap(long, default_value = "/run/vm-doc-portal")]
     guest_mountpoint: PathBuf,
 
+    /// Mappings from guest paths to host paths for passthrough file systems (for file transfer), in guest=host format
+    #[clap(long)]
+    path_mapping: Vec<String>,
+
     /// Vsock port number to listen on for the VM bus
     #[clap(long)]
     vsock_port: Option<u32>,
@@ -65,11 +70,31 @@ async fn new_hosted_bus() -> eyre::Result<(
     Ok((Arc::new(Mutex::new(bus)), guid, owner_stream))
 }
 
+fn parse_path_mapping(s: &str) -> eyre::Result<(PathBuf, PathBuf)> {
+    let mut split = s.split('=');
+    let guest_path = PathBuf::from(split.next().ok_or_eyre("failed to split mapping")?);
+    let host_path = PathBuf::from(split.next().ok_or_eyre("failed to split mapping")?);
+    Ok((guest_path, host_path))
+}
+
 #[tokio::main]
 async fn main() -> eyre::Result<()> {
     tracing_subscriber::fmt::init();
 
     let cli = BrokerCli::parse();
+    let mut path_prefix_to_host: Vec<(PathBuf, PathBuf)> = cli
+        .path_mapping
+        .iter()
+        .flat_map(|arg| match parse_path_mapping(arg) {
+            Ok(mapping) => Some(mapping),
+            Err(err) => {
+                error!(?err, %arg, "could not parse path mapping");
+                None
+            }
+        })
+        .collect();
+    path_prefix_to_host.sort_unstable_by_key(|(prefix, _)| -(prefix.as_os_str().len() as isize));
+    debug!(?path_prefix_to_host, "parsed path mappings");
 
     let (priv_bus, _, mut priv_lst) = new_hosted_bus().await?;
 
@@ -153,6 +178,7 @@ async fn main() -> eyre::Result<()> {
         &host_session_conn,
         &priv_bus_conn,
         cli.guest_mountpoint,
+        path_prefix_to_host,
     )
     .await?;
     let notification_imp = portal::notification::Notification::new(&host_session_conn).await?;