[pbs-devel] [PATCH proxmox-backup v4] client: mount: wait for child to return before exiting

[Gabriel Goller]

When using the `proxmox-backup-client mount` command, the parent sometimes
exits before we can print any error message. Most notably this happens
when no PBS_REPOSITORY is passed, as this is the first option checked.
If the underlying file descriptor has been closed, wait for the client
to complete and return the error message.

Reported-by: Friedrich Weber <f.weber at proxmox.com>
Suggested-by: Christian Ebner <c.ebner at proxmox.com>
Signed-off-by: Gabriel Goller <g.goller at proxmox.com>
---

v4, thanks @Wobu:
 - Use [u8] instead of Vec

v3, thanks @Christian, @Friedrich:
 - Removed stdout/stderr flush (which didn't solve the problem)
 - Wait for child to finish

v2, thanks @Christian:
 - Removed unneeded pw.try_clone()
 proxmox-backup-client/src/mount.rs | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/proxmox-backup-client/src/mount.rs b/proxmox-backup-client/src/mount.rs
index b69e7e80..ee7cfec2 100644
--- a/proxmox-backup-client/src/mount.rs
+++ b/proxmox-backup-client/src/mount.rs
@@ -183,7 +183,17 @@ fn mount(
         Ok(ForkResult::Parent { .. }) => {
             drop(pw);
             // Blocks the parent process until we are ready to go in the child
-            let _res = nix::unistd::read(pr.as_raw_fd(), &mut [0]).unwrap();
+            let mut buffer = [0u8];
+            nix::unistd::read(pr.as_raw_fd(), &mut buffer).unwrap();
+
+            // Read buffer didn't change, which indicates that nothing has been read and the file
+            // descriptor has probably been closed. This means that there was an error in the child
+            // process and it did not daemonize correctly.
+            if buffer[0] == 0 {
+                // Wait for the child process to finish, so it can return a nice error.
+                nix::sys::wait::wait().unwrap();
+            }
+
             Ok(Value::Null)
         }
         Ok(ForkResult::Child) => {
@@ -264,7 +274,7 @@ async fn mount_do(param: Value, pipe: Option<OwnedFd>) -> Result<Value, Error> {
             }
             // Signal the parent process that we are done with the setup and it can
             // terminate.
-            nix::unistd::write(pipe.as_raw_fd(), &[0u8])?;
+            nix::unistd::write(pipe.as_raw_fd(), &[1u8])?;
             let _: OwnedFd = pipe;
         }
 
-- 
2.43.0