M7 Phase 1: /proc Root Directory PID Enumeration

The /proc filesystem has existed in Kevlar since M5, but it had a blind spot: readdir("/proc/") only returned the 10 static files (cpuinfo, meminfo, mounts, etc.). It never enumerated live PIDs or showed the self symlink. Any program that iterates /proc to discover processes — ps, top, htop, systemd's process tracker — would see an empty process list.

Phase 1 closes this gap. ls /proc now shows self, every live PID directory, and all static files.

The gap

ProcRootDir already handled lookups correctly: open("/proc/42/stat") worked because lookup() parsed numeric names and constructed ProcPidDir on the fly. But readdir() — the function behind getdents64(2) — only delegated to the underlying tmpfs, which knew about the 10 static files and nothing else.

The fix has two parts: a way to enumerate PIDs, and a readdir that stitches static entries, self, and PIDs together.

list_pids()

The process table is a SpinLock<BTreeMap<PId, Arc<Process>>>. We already had process_count() that locks and returns .len(). The new list_pids() follows the same pattern:

#![allow(unused)]
fn main() {
pub fn list_pids() -> Vec<PId> {
    PROCESSES.lock().keys().cloned().collect()
}
}

BTreeMap iteration yields keys in sorted order, so the PID list comes out naturally sorted — ls /proc shows 1 2 3 ... without extra work.

Stitched readdir

The readdir protocol is index-based: the VFS calls readdir(0), readdir(1), readdir(2), etc., until it gets None. Our readdir partitions the index space into three regions:

Static entries (indices 0..N): delegated to the tmpfs directory (metrics, mounts, cpuinfo, meminfo, stat, version, etc.)
"self" symlink (index N): a DirEntry with FileType::Link
PID directories (indices N+1..): one DirEntry per live process with FileType::Directory and the PID as the name

When the static directory exhausts its entries, we count how many it had and use the remainder as an offset into the dynamic entries.

Contract test

The new proc_mount.c contract test verifies four things:

readdir("/proc/") contains a self entry
readdir("/proc/") contains at least one numeric PID entry
readlink("/proc/self") resolves to the current process's PID
/proc/1/stat is readable

This runs on both Linux and Kevlar through the contract comparison framework. Both produce identical output: proc_readdir_self: ok, proc_readdir_pid: ok, proc_self_readlink: ok, proc_1_stat: ok, CONTRACT_PASS.

Results

20/20 contract tests pass, including the new proc_mount test. No regressions in existing tests.

What's next

Phase 2 enriches the global /proc files. Most of these already exist (/proc/cpuinfo, /proc/version, /proc/meminfo, /proc/mounts) but need verification against glibc's expectations and multi-CPU accuracy for /proc/cpuinfo. The goal is that every file ls /proc shows is actually readable with correct content.

Kevlar Documentation