From 5dcfade5f102256de787b2157b01293160780411 Mon Sep 17 00:00:00 2001 From: Gabriel Schneider Date: Mon, 21 Sep 2026 22:37:06 -0300 Subject: Make a pane by opening /pane/new, and a Plan 9 idiom pass The Tcreate that replaced acme's /new was a step away from the idiom dressed up as a step toward it. A pane is named by a server-assigned serial, so the create ignored the client's name: `mkdir /pane/foo` succeeded and left you /pane/12. A mkdir that does not make the directory you named is worse than the read-with-side-effect it replaced, and it broke in the shell workflow that motivated the change. `create` is out of the declared features, so Tcreate is EPERM again; Tremove stays, since `rm` to close a pane is unambiguously right. /pane/new is now opened, not created: the open makes the pane, the read of that fid answers its serial, two reads agree, and closing it leaves the pane. That is /net/tcp/clone's mechanism (kernel/network/ip/devip.c, in ipopen), not acme's, and the difference is deliberate. acme allocates during the walk and lands inside the new window, so /dev/new/body works in one step, and it can afford to list `new` because a Plan 9 directory read carries every entry's stat and nothing walks. A kernel or FUSE mount walks and stats each name a listing gave it, so allocate-on-walk would make a pane per `ls -l`. Allocating on open keeps `new` listed -- a stat is not an open -- at the cost of the one-step new/body. `new` stays unreachable from an editor path, because that resolution serves Look hover previews. The idiom pass behind it, read out of the Plan 9 tree at ~/05-genizah/principia-softwarica rather than recalled: Rerror carries a string, not an errno (man 5 error: `ename[s]`), and acme names every refusal. The five refusals pardes shares with acme now say what they mean; the generic sites keep their bare errno rather than invent strings acme does not have. body and tag declare DMAPPEND, which they had always behaved as (acme(4): "always appended; the file offset is ignored"), checked first against Linux's fs/9p, which never maps the bit. excl stays unset everywhere, because acme sets DMEXCL on nothing. Blocking reads, per-object addr scope and the readable pane ctl were already right. Real stat sizes and qid versions stay: acme reports length 0 and version 0 for everything, and Linux clients need better. One bug fell out of it. open reset the addr range, so `echo '#0,#5' >addr; cat addr` answered `0 0` and `cp addr dot` copied zeros. acme(4) makes the contract explicit -- "a regular expression may be evaluated by writing it to addr and reading it back" -- and acme gets away with resetting on the 0-to-1 open only because its clients hold the fid across both. A shell cannot: that is two opens. The register is cleared by truncating it now. Co-Authored-By: Claude Opus 5 (1M context) --- src/ninep/pane.zig | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'src/ninep/pane.zig') diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig index 42c0c48e..4b34cf96 100644 --- a/src/ninep/pane.zig +++ b/src/ninep/pane.zig @@ -24,6 +24,12 @@ const Node = tree.Node; /// Filesystem state a pane carries beside its editor state. pub const State = struct { + /// The range `data` and `xdata` read and write through. acme clears it + /// when the first client opens `addr` (editors/acme/xfid.c:105), which + /// suits a client that holds the fid open and leaves a shell reading back + /// `0 0` from the address it just wrote. Here it is the pane's own + /// register, cleared by truncating the file, so that `cp addr dot` and + /// `cat addr` answer what was written. addr: Range = .{}, limit: ?Range = null, readers: u16 = 0, @@ -458,7 +464,7 @@ fn writeRange(p: *Pardes, req: Req, id: usize, pane: *Pane, file: PaneFile) Repl const pf = &p.fs.panes[id]; const text = bodyOf(pane); clampAddr(pf, text.len); - const r = rangeOf(pf, text, req.data) orelse return Reply.fail(req.tag, E.INVAL); + const r = rangeOf(pf, text, req.data) orelse return tree.failText(req.tag, E.INVAL, tree.e_bad_addr); switch (file) { .addr => pf.addr = r, .limit => pf.limit = r, -- cgit v1.3