agent: don't error of virtiofs share is already mounted

Port kata-containers/agent#883 to the Rust Agent.

In the event that the virtiofs device is already mounted at the
requested destination, don't error out. We'll check before attempting to
mount to see if the destination is already a mount point. If so, skip
doing the mount in the agent.

This facilitates mounting the sharedfs automatically in the guest before
the agent service starts.

Signed-off-by: Eric Ernst eric.g.ernst@gmail.com

Fixes: #1398

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

src/agent/src/mount.rs

@@ -44,6 +44,8 @@ pub const DRIVER_LOCAL_TYPE: &str = "local";
 
 pub const TYPE_ROOTFS: &str = "rootfs";
 
+pub const MOUNT_GUEST_TAG: &str = "kataShared";
+
 #[rustfmt::skip]
 lazy_static! {
     pub static ref FLAGS: HashMap<&'static str, (bool, MsFlags)> = {
@@ -383,6 +385,14 @@ async fn nvdimm_storage_handler(
 fn mount_storage(logger: &Logger, storage: &Storage) -> Result<()> {
     let logger = logger.new(o!("subsystem" => "mount"));
 
+    // Check share before attempting to mount to see if the destination is already a mount point.
+    // If so, skip doing the mount. This facilitates mounting the sharedfs automatically
+    // in the guest before the agent service starts.
+    if storage.source == MOUNT_GUEST_TAG && is_mounted(&storage.mount_point)? {
+        warn!(logger, "kataShared already mounted, ignoring...");
+        return Ok(());
+    }
+
     match storage.fstype.as_str() {
         DRIVER_9P_TYPE | DRIVER_VIRTIOFS_TYPE => {
             let dest_path = Path::new(storage.mount_point.as_str());
@@ -418,6 +428,24 @@ fn mount_storage(logger: &Logger, storage: &Storage) -> Result<()> {
     bare_mount.mount()
 }
 
+/// Looks for `mount_point` entry in the /proc/mounts.
+fn is_mounted(mount_point: &str) -> Result<bool> {
+    let mount_point = mount_point.trim_end_matches('/');
+    let found = fs::metadata(mount_point).is_ok()
+        // Looks through /proc/mounts and check if the mount exists
+        && fs::read_to_string("/proc/mounts")?
+            .lines()
+            .any(|line| {
+                // The 2nd column reveals the mount point.
+                line.split_whitespace()
+                    .nth(1)
+                    .map(|target| mount_point.eq(target))
+                    .unwrap_or(false)
+            });
+
+    Ok(found)
+}
+
 fn parse_mount_flags_and_options(options_vec: Vec<&str>) -> (MsFlags, String) {
     let mut flags = MsFlags::empty();
     let mut options: String = "".to_string();
@@ -897,6 +925,14 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_is_mounted() {
+        assert!(is_mounted("/proc").unwrap());
+        assert!(!is_mounted("").unwrap());
+        assert!(!is_mounted("!").unwrap());
+        assert!(!is_mounted("/not_existing_path").unwrap());
+    }
+
     #[test]
     fn test_remove_mounts() {
         skip_if_not_root!();