tools/daemon: dup the TcpListener file descriptor

Now that we let hyper shutdown gracefully we need an owned
version of the listening socket to prevent it from closing
before running the reload preparations.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/tools/daemon.rs

@@ -1,7 +1,7 @@
 //! Helpers for daemons/services.
 
 use std::ffi::CString;
-use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 use std::os::unix::ffi::OsStrExt;
 use std::panic::UnwindSafe;
 
@@ -9,16 +9,16 @@ use failure::*;
 use tokio::prelude::*;
 
 use crate::server;
-use crate::tools::fd_change_cloexec;
+use crate::tools::{fd_change_cloexec, self};
 
 // Unfortunately FnBox is nightly-only and Box<FnOnce> is unusable, so just use Box<Fn>...
-pub type BoxedStoreFunc = Box<dyn Fn() -> Result<String, Error> + UnwindSafe + Send>;
+pub type BoxedStoreFunc = Box<dyn FnMut() -> Result<String, Error> + UnwindSafe + Send>;
 
 /// Helper trait to "store" something in the environment to be re-used after re-executing the
 /// service on a reload.
 pub trait Reloadable: Sized {
     fn restore(var: &str) -> Result<Self, Error>;
-    fn get_store_func(&self) -> BoxedStoreFunc;
+    fn get_store_func(&self) -> Result<BoxedStoreFunc, Error>;
 }
 
 /// Manages things to be stored and reloaded upon reexec.
@@ -58,13 +58,13 @@ impl Reloader {
 
         self.pre_exec.push(PreExecEntry {
             name,
-            store_fn: res.get_store_func(),
+            store_fn: res.get_store_func()?,
         });
         Ok(res)
     }
 
     fn pre_exec(self) -> Result<(), Error> {
-        for item in self.pre_exec {
+        for mut item in self.pre_exec {
             std::env::set_var(item.name, (item.store_fn)()?);
         }
         Ok(())
@@ -124,12 +124,15 @@ impl Reloadable for tokio::net::TcpListener {
     // NOTE: The socket must not be closed when the store-function is called:
     // FIXME: We could become "independent" of the TcpListener and its reference to the file
     // descriptor by `dup()`ing it (and check if the listener still exists via kcmp()?)
-    fn get_store_func(&self) -> BoxedStoreFunc {
-        let fd = self.as_raw_fd();
-        Box::new(move || {
-            fd_change_cloexec(fd, false)?;
-            Ok(fd.to_string())
-        })
+    fn get_store_func(&self) -> Result<BoxedStoreFunc, Error> {
+        let mut fd_opt = Some(tools::Fd(
+            nix::fcntl::fcntl(self.as_raw_fd(), nix::fcntl::FcntlArg::F_DUPFD_CLOEXEC(0))?
+        ));
+        Ok(Box::new(move || {
+            let fd = fd_opt.take().unwrap();
+            fd_change_cloexec(fd.as_raw_fd(), false)?;
+            Ok(fd.into_raw_fd().to_string())
+        }))
     }
 
     fn restore(var: &str) -> Result<Self, Error> {