fuse_loop: add automatic cleanup of run files and dangling instances

A 'map' call will only clean up what it needs, that is only leftover
files or dangling instances of it's own name.

For a full cleanup the user can call 'unmap' without any arguments.

The 'cleanup on error' behaviour of map_loop is removed. It is no longer
needed (since the next call will clean up anyway), and in fact fixes a
bug where trying to map an image twice would result in an error, but
also cleanup the .pid file of the running instance, causing 'unmap' to
fail afterwards.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

src/bin/proxmox_backup_client/mount.rs

@@ -83,7 +83,8 @@ const API_METHOD_UNMAP: ApiMethod = ApiMethod::new(
         "Unmap a loop device mapped with 'map' and release all resources.",
         &sorted!([
             ("name", true, &StringSchema::new(
-                "Archive name, path to loopdev (/dev/loopX) or loop device number. Omit to list all current mappings."
+                concat!("Archive name, path to loopdev (/dev/loopX) or loop device number. ",
+                        "Omit to list all current mappings and force cleaning up leftover instances.")
             ).schema()),
         ]),
     )
@@ -337,6 +338,7 @@ fn unmap(
     let mut name = match param["name"].as_str() {
         Some(name) => name.to_owned(),
         None => {
+            tools::fuse_loop::cleanup_unused_run_files(None);
             let mut any = false;
             for (backing, loopdev) in tools::fuse_loop::find_all_mappings()? {
                 let name = tools::systemd::unescape_unit(&backing)?;

src/tools/fuse_loop.rs

@@ -15,7 +15,7 @@ use tokio::io::{AsyncRead, AsyncSeek, AsyncReadExt, AsyncSeekExt};
 use futures::stream::{StreamExt, TryStreamExt};
 use futures::channel::mpsc::{Sender, Receiver};
 
-use proxmox::{try_block, const_regex};
+use proxmox::const_regex;
 use proxmox_fuse::{*, requests::FuseRequest};
 use super::loopdev;
 use super::fs;
@@ -55,6 +55,11 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
         let mut pid_path = path.clone();
         pid_path.set_extension("pid");
 
+        // cleanup previous instance with same name
+        // if loopdev is actually still mapped, this will do nothing and the
+        // create_new below will fail as intended
+        cleanup_unused_run_files(Some(name.as_ref().to_owned()));
+
         match OpenOptions::new().write(true).create_new(true).open(&path) {
             Ok(_) => { /* file created, continue on */ },
             Err(e) => {
@@ -66,7 +71,6 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
             },
         }
 
-        let res: Result<(Fuse, String), Error> = try_block!{
         let session = Fuse::builder("pbs-block-dev")?
             .options_os(options)?
             .enable_read()
@@ -80,11 +84,6 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
         // write pidfile so unmap can later send us a signal to exit
         Self::write_pidfile(&pid_path)?;
 
-            Ok((session, loopdev_path))
-        };
-
-        match res {
-            Ok((session, loopdev_path)) =>
         Ok(Self {
             session: Some(session),
             reader,
@@ -92,14 +91,7 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
             fuse_path: path.to_string_lossy().into_owned(),
             pid_path: pid_path.to_string_lossy().into_owned(),
             loopdev_path,
-                }),
-            Err(e) => {
-                // best-effort temp file cleanup in case of error
-                let _ = remove_file(&path);
-                let _ = remove_file(&pid_path);
-                Err(e)
-            }
-        }
+        })
     }
 
     fn write_pidfile(path: &Path) -> Result<(), Error> {
@@ -229,6 +221,38 @@ impl<R: AsyncRead + AsyncSeek + Unpin> FuseLoopSession<R> {
     }
 }
 
+/// Clean up leftover files as well as FUSE instances without a loop device
+/// connected. Best effort, never returns an error.
+/// If filter_name is Some("..."), only this name will be cleaned up.
+pub fn cleanup_unused_run_files(filter_name: Option<String>) {
+    if let Ok(maps) = find_all_mappings() {
+        for (name, loopdev) in maps {
+            if loopdev.is_none() &&
+                (filter_name.is_none() || &name == filter_name.as_ref().unwrap())
+            {
+                let mut path = PathBuf::from(RUN_DIR);
+                path.push(&name);
+
+                // clean leftover FUSE instances (e.g. user called 'losetup -d' or similar)
+                // does nothing if files are already stagnant (e.g. instance crashed etc...)
+                if let Ok(_) = unmap_from_backing(&path) {
+                    // we have reaped some leftover instance, tell the user
+                    eprintln!(
+                        "Cleaned up dangling mapping '{}': no loop device assigned",
+                        &name
+                    );
+                }
+
+                // remove remnant files
+                // these we're not doing anything, so no need to inform the user
+                let _ = remove_file(&path);
+                path.set_extension("pid");
+                let _ = remove_file(&path);
+            }
+        }
+    }
+}
+
 fn get_backing_file(loopdev: &str) -> Result<String, Error> {
     let num = loopdev.split_at(9).1.parse::<u8>().map_err(|err|
         format_err!("malformed loopdev path, does not end with valid number - {}", err))?;