Add support for getpgrp/getpgid/setpgid/TIOCGPGRP/TIOCSPGRP by wdcui · Pull Request #640 · microsoft/litebox

wdcui · 2026-02-04T21:16:40Z

This PR adds the support for getpgrp/getpgid/setpgid/TIOCGPGRP/TIOCSPGRP.

- Add Getpgrp variant to SyscallRequest enum in litebox_common_linux - Add syscall number mapping for Sysno::getpgrp - Implement sys_getpgrp() in litebox_shim_linux/syscalls/process.rs - Add dispatch case for SyscallRequest::Getpgrp in litebox_shim_linux - Add unit test for getpgrp syscall The getpgrp syscall returns the process group ID. This implementation returns the process ID, which is the default behavior for a process that hasn't explicitly joined another process group via setpgid. This is required for bash initialization.

- Add TIOCGPGRP constant (0x540F) to litebox_common_linux - Add TIOCGPGRP variant to IoctlArg enum - Add TIOCGPGRP to ioctl syscall parsing - Implement TIOCGPGRP handler in litebox_shim_linux/syscalls/file.rs TIOCGPGRP returns the process group ID of the foreground process group on the terminal. In LiteBox's simplified model, each process forms its own process group where PGID equals PID. This is required for bash shell initialization along with getpgrp syscall.

CvvT · 2026-02-04T21:29:58Z

litebox_shim_linux/src/syscalls/file.rs

+                // In LiteBox, processes are simplified: each process forms its own process group
+                // where the process group ID equals the process ID. This is a simplification
+                // compared to standard Unix where processes can explicitly join different groups.
+                let pid = self.sys_getpid();


TIOCGPGRP is not equivalent to getpgrp, it returns the pgid of the foreground process on the terminal. If litebox is running in background, it should not return its own pid. I'm not sure here what value we should return as the foreground process on the terminal is outside LiteBox. Maybe just log and return an error code for now?

Fixed. I added TIOCSPGRP.

CvvT · 2026-02-04T21:41:11Z

litebox_shim_linux/src/syscalls/process.rs

+    /// explicitly joined another process group via `setpgid`.
+    pub(crate) fn sys_getpgrp(&self) -> i32 {
+        // In a full implementation, we'd track pgid separately. For now, return pid
+        // which is the default pgid for a new process.


For a forked process, the pgid is the same as its parent, but right now we don't support fork yet. Should we just implement setpgid if it is simple for an agent to do?

Yes, added the support for setpgid.

… group support Extends the partial getpgrp/TIOCGPGRP implementation with proper pgrp tracking per task, setpgid/getpgid syscalls, and TIOCSPGRP ioctl backed by a global foreground process group state. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

github-actions · 2026-02-05T05:16:45Z

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_no_repr_variant_discriminant_changed: enum variant had its discriminant change value ---

Description:
The enum's variant had its discriminant value change. This breaks downstream code that used its value via a numeric cast like `as isize`.
        ref: https://doc.rust-lang.org/reference/items/enumerations.html#assigning-discriminant-values
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/enum_no_repr_variant_discriminant_changed.ron

Failed in:
  variant SyscallRequest::Getuid 78 -> 81 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2234
  variant SyscallRequest::Geteuid 79 -> 82 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2235
  variant SyscallRequest::Getgid 80 -> 83 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2236
  variant SyscallRequest::Getegid 81 -> 84 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2237
  variant SyscallRequest::Sysinfo 82 -> 85 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2238
  variant SyscallRequest::CapGet 83 -> 86 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2241
  variant SyscallRequest::GetDirent64 84 -> 87 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2245
  variant SyscallRequest::SchedGetAffinity 85 -> 88 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2250
  variant SyscallRequest::SchedYield 86 -> 89 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2255
  variant SyscallRequest::Futex 87 -> 90 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2256
  variant SyscallRequest::Execve 88 -> 91 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2259
  variant SyscallRequest::Umask 89 -> 92 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2264
  variant SyscallRequest::Prctl 90 -> 93 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2267
  variant SyscallRequest::Alarm 91 -> 94 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2270
  variant SyscallRequest::SetITimer 92 -> 95 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2273

CvvT · 2026-02-06T21:57:13Z

litebox_shim_linux/src/syscalls/process.rs

+        if pid == 0 || pid == self.pid {
+            Ok(self.pgrp.load(core::sync::atomic::Ordering::Relaxed))
+        } else {
+            Err(Errno::ESRCH)


ERRORS [top](https://man7.org/linux/man-pages/man3/getpgid.3p.html#top_of_page) The getpgid() function shall fail if: EPERM The process whose process ID is equal to pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of that process from the calling process. ESRCH There is no process with a process ID equal to pid. The getpgid() function may fail if: EINVAL The value of the pid argument is invalid.

Add some comment here? Currently there is only process so we always return ESRCH.

CvvT · 2026-02-06T22:10:27Z

litebox_shim_linux/src/syscalls/process.rs

+            return Err(Errno::EINVAL);
+        }
+        if target_pid != self.pid {
+            return Err(Errno::ESRCH);


CvvT · 2026-02-06T22:33:46Z

litebox_shim_linux/src/syscalls/process.rs

+        self.pgrp
+            .store(target_pgid, core::sync::atomic::Ordering::Relaxed);


We should add some check to ensure that pgid is valid. Since we only have one process, we can just return an error if pgid differs from the current one. Don't need to change pgid at all.

CvvT · 2026-02-06T22:40:21Z

litebox_shim_linux/src/lib.rs

            boot_time: self.platform.now(),
            load_filter: self.load_filter,
            next_thread_id: 2.into(), // start from 2, as 1 is used by the main thread
+            fg_pgrp: core::sync::atomic::AtomicI32::new(1),


In LiteBox, there is no concept of forground and background process. Initializing it to 1 indicates that LiteBox always runs in foreground, but I can also run it in background (cargo run -p litebox_runner_linux_userland ... &). In the latter case, LiteBox does not control the foreground process. Depending on how applications use this syscall, we may have different designs. For now, maybe we could just return some error code and print out some warnings.

wdcui added 2 commits February 4, 2026 05:41

wdcui requested a review from CvvT February 4, 2026 21:16

CvvT reviewed Feb 4, 2026

View reviewed changes

wdcui force-pushed the wdcui/implement-getpgrp-syscall branch from 5e3ab6a to bf807a4 Compare February 5, 2026 04:46

Fix process group sharing and validation

7f62435

wdcui changed the title ~~Add support for getpgrp~~ Add support for getpgrp/getpgid/setpgid/TIOCGPGRP/TIOCSPGRP Feb 5, 2026

CvvT reviewed Feb 6, 2026

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add support for getpgrp/getpgid/setpgid/TIOCGPGRP/TIOCSPGRP#640

Add support for getpgrp/getpgid/setpgid/TIOCGPGRP/TIOCSPGRP#640
wdcui wants to merge 4 commits intomainfrom
wdcui/implement-getpgrp-syscall

wdcui commented Feb 4, 2026 •

edited

Loading

Uh oh!

CvvT Feb 4, 2026

Uh oh!

wdcui Feb 5, 2026

Uh oh!

CvvT Feb 4, 2026

Uh oh!

wdcui Feb 5, 2026

Uh oh!

github-actions bot commented Feb 5, 2026

Uh oh!

CvvT Feb 6, 2026

Uh oh!

CvvT Feb 6, 2026

Uh oh!

CvvT Feb 6, 2026

Uh oh!

CvvT Feb 6, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

		self.pgrp
		.store(target_pgid, core::sync::atomic::Ordering::Relaxed);

Conversation

wdcui commented Feb 4, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

github-actions bot commented Feb 5, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

wdcui commented Feb 4, 2026 •

edited

Loading