9ns --mntgen: a server that never answers stalls only its own name

2026-09-22T14:39:25Z

Opening a fish (self-wrapped in `9ns --mntgen`) and running an agent in it would sometimes freeze the whole session: no input reached it and nothing under /mnt/9p answered, until the shell was killed from outside. The cause was one posted server that accepted a connection and then never spoke 9P — pardes, answering its 9P from the same loop that was walking its own mount, was the one on this machine, but any wedged or half-dead server does it. Three things conspired, and each is fixed on its own: * The dispatcher dialed. A LOOKUP of an undialed name ran connect, Tversion, Tattach and Tstat on the one thread that reads /dev/fuse, so while that server kept quiet no request for any name was read, and no FUSE_INTERRUPT either. Now the dispatcher makes a Mount without touching the network and queues the walk to the mount's worker, which dials while serving it. The dial is the request in flight, so an interrupt of the walk abandons it at once (`Session.abort_on_cancel`: nothing to flush before a session exists) and the walk answers EINTR; a failed dial leaves the mount undialed for the next walk to retry; a full listen backlog (the server stopped accepting) is retried for 5s and then EIO. Every later LOOKUP of the name goes through the same queue and is answered from the remembered root attr, so the dispatcher never holds a session at all. * Once the dispatcher had read a request the process behind it was unkillable (FUSE waits out a request userspace has taken), and an INTERRUPT for a request still sitting in a mount's queue was dropped. The dispatcher now takes a queued request out and answers EINTR itself, and forwards only in-flight ones to the worker; queue and in-flight unique are read under the mount's mutex, where the worker moves a request from one to the other. A Tflush the server never answers is given 3s (`Session.flush_grace_ms`) and then the session is declared wedged: the request answers EINTR, the mount dies, the next walk makes a new one. * The kernel serialized the directory. Without FUSE_PARALLEL_DIROPS in the INIT reply every LOOKUP and READDIR in a directory takes its inode lock, so one parked walk held up every other name under /mnt/9p however free the dispatcher was (`cat` sat in fuse_lock_inode). The flag is now negotiated when the kernel offers it. What remains is the kernel's own serialization of lookups of one *name*: a second walker into the parked name waits for the first walk to end, and only then proceeds (and can be interrupted in its turn). An adversarial review of the above found three more things, fixed here: the single-connection bridge's one-slot stash stopped polling the FUSE fd while a second request was parked, so an INTERRUPT could not arrive (and parallel dirops make a second request routine) — the stash is now a queue of copies and the fd is always watched; a dead or wedged mount kept its socket open until exit, where a late-answering single-threaded server could block on it — the session is closed when the mount dies; and teardown after DESTROY or ENODEV (the child still alive, so stop_fd says nothing) could join a worker parked on a mute server forever — the sockets are shut down before the join. The flush grace is a deadline now, not a timer restarted on every wakeup. A black-box run against the binary (hostile servers: mute, garbage, close-after-accept, full backlog, 100 mute names, interrupt storms, 300 deaths of one server) found that a dead mount kept its socket, its interrupt pipe and a megabyte of buffers until exit — three descriptors per death — so `retire` now frees all of it and keeps only the slot; descriptors, threads and RSS stay flat across 400 deaths. The 4096-slot cap per process remains and is documented. Reproduced with a socket that accepts and never writes, posted beside 9agents in a scratch registry: before, `cat /mnt/9p/agents/pid` parked behind `stat /mnt/9p/hang` and SIGINT did nothing; after, it answers at once, the parked walker dies of its signal within milliseconds, and a server that answers the handshake but ignores reads and Tflush releases its reader after the grace. mntgen.sh and adv_bridge_interrupt.sh now check exactly that; nine.zig gains unit tests for the grace and the abort. Also in this change: the uncommitted ESTALE-on-death and FUSE_NOTIFY_INVAL_ENTRY work from the working copy, which the dead-mount path here builds on. Co-Authored-By: Claude Fable 5.1

9ns: --name and /mnt/9p/ mounts, qid.path as inode number, interrupts as Tflush

2026-09-20T02:55:47Z

- --name NAME (default derived from the transport: socket basename, tcp-IP-PORT, spawned command, fdN) mounts at /mnt/9p/; --mount still overrides. ensureMountpoint walks down and creates missing components, shadowing the deepest unwritable ancestor. NINE_MOUNT is the only exported variable. - The inode number reported to the kernel is the 9P qid.path for every node, root included; a server handing qid.path 1 to a file (Pardes /self) no longer collides with the root. - FUSE_INTERRUPT for the request in flight becomes Tflush; a blocked read returns EINTR when the server answers the flush, chunked transfers return short counts, other requests arriving meanwhile are stashed and served next. Servers ignoring Tflush still block until they answer. - 9ns-test now covers nine/bridge/fuse; new adv_bridge_interrupt suite (28); 9ns-itest grows to 88 checks. Co-Authored-By: Claude Fable 5.1

Rename programs: 9player -> 9ns, introspect -> 9proc, app -> web (9web)

2026-09-20T02:28:22Z

Directories, binaries, build options (-D9ns, -D9proc), step names, module name (9proc), thread and fs names, env var NINEPLAYER_MOUNT -> NINE_MOUNT, docs and test scripts. Browser assets move to web/static. Co-Authored-By: Claude Fable 5.1

cloud9.git/9ns/src/fuse.zig, branch main

9ns --mntgen: a server that never answers stalls only its own name

9ns: --name and /mnt/9p/ mounts, qid.path as inode number, interrupts as Tflush

Rename programs: 9player -> 9ns, introspect -> 9proc, app -> web (9web)