fix(redox): translate POSIX F_DUPFD_CLOEXEC (1030) to Redox syscall ABI (5)

fcntl(F_DUPFD_CLOEXEC) reached redox_rt/kernel with the POSIX/C value 1030
instead of the Redox syscall value (syscall::F_DUPFD_CLOEXEC=5). redox_rt did
not recognize it as a dup, forwarded the raw command to the kernel, and the
kernel's fcntl fell through to its EINVAL catch-all. That made
OwnedFd::try_clone() return EINVAL, which broke tokio Runtime::build() (its I/O
reactor try_clones the epoll fd) for every tokio user on Redox: all the zbus
system daemons (sessiond/polkit/udisks/upower) and the login shell. F_DUPFD and
plain dup worked because they share the same value in both namespaces;
F_DUPFD_CLOEXEC was the sole untranslated command.

Also drop the ineffective epoll_ctl EINVAL/EBADF retry loop: it was based on a
disproven 'transient scheme churn' theory; epoll registrations always succeed
immediately. The real dup failure is fixed above.

src/platform/redox/epoll.rs

@@ -64,36 +64,7 @@ impl PalEpoll for Sys {
                     // systems. If this is needed, use a box or something
                     data: unsafe { (*event).data.u64 as usize },
                 };
-                // Registering an fd with /scheme/event can transiently fail
+                Sys::write(epfd, &ev)?;
-                // with EINVAL/EBADF while the scheme backing `fd` is still
-                // starting up or the fd-table is churning during early boot
-                // (e.g. a tokio/mio reactor built by a daemon that races ahead
-                // of ipcd's uds_stream scheme). Without recovery, tokio's
-                // Runtime::build aborts the whole runtime, killing every
-                // zbus-based daemon and any tokio program (including the login
-                // shell). Retry with a short backoff so the registration
-                // succeeds once the scheme settles; a genuinely permanent
-                // failure still surfaces after the bounded window. This mirrors
-                // the park-path recovery in the P0-epoll-redox-recovery tokio
-                // patch, but at the registration site the patch cannot reach.
-                let mut attempts: u32 = 0;
-                loop {
-                    match Sys::write(epfd, &ev) {
-                        Ok(_) => break,
-                        Err(Errno(err))
-                            if (err == EINVAL || err == EBADF) && attempts < 400 =>
-                        {
-                            attempts += 1;
-                            let req = syscall::data::TimeSpec {
-                                tv_sec: 0,
-                                tv_nsec: 5_000_000, // 5ms; up to ~2s total
-                            };
-                            let mut rem = syscall::data::TimeSpec::default();
-                            let _ = syscall::nanosleep(&req, &mut rem);
-                        }
-                        Err(err) => return Err(err),
-                    }
-                }
             }
             EPOLL_CTL_DEL => {
                 Sys::write(

src/platform/redox/mod.rs

@@ -477,7 +477,24 @@ impl Pal for Sys {
             _ => {}
         }
 
-        Ok(redox_rt::sys::fcntl(fd as usize, cmd as usize, args as usize)? as c_int)
+        // The POSIX/C value of `F_DUPFD_CLOEXEC` exposed by <fcntl.h> (1030,
+        // matching Linux so that libc/std/mio hardcode it) does NOT match the
+        // Redox syscall-ABI value that redox_rt and the kernel understand
+        // (`syscall::F_DUPFD_CLOEXEC`, 5). Every other fcntl command that reaches
+        // redox_rt shares the same numeric value in both namespaces, so
+        // F_DUPFD_CLOEXEC is the single command that must be translated here.
+        // Without this, redox_rt does not recognize 1030 as a dup, forwards the
+        // raw command to the kernel, and the kernel's fcntl falls through to its
+        // catch-all EINVAL arm. That made `OwnedFd::try_clone()` fail with
+        // EINVAL, which in turn broke `tokio::runtime::Builder::build()` (its I/O
+        // reactor try_clones the epoll fd) for every tokio user on Redox — all
+        // the zbus system daemons and the login shell.
+        let redox_cmd = if cmd == fcntl::F_DUPFD_CLOEXEC {
+            syscall::F_DUPFD_CLOEXEC
+        } else {
+            cmd as usize
+        };
+        Ok(redox_rt::sys::fcntl(fd as usize, redox_cmd, args as usize)? as c_int)
     }
 
     fn fdatasync(fd: c_int) -> Result<()> {