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/testing.zig | 26 +++++++------------------- 1 file changed, 7 insertions(+), 19 deletions(-) (limited to 'src/ninep/testing.zig') diff --git a/src/ninep/testing.zig b/src/ninep/testing.zig index ad1d84e4..44329eee 100644 --- a/src/ninep/testing.zig +++ b/src/ninep/testing.zig @@ -69,26 +69,14 @@ pub fn look_up(p: *Pardes, dir: u64, name: []const u8) Answer { return call(p, .{ .tag = 3, .op = .lookup, .node = dir, .data = name }); } -/// Creates a pane in /pane, as a client's mkdir does, and returns its serial. +/// Makes a pane the way a client does, by walking to /pane/new, and answers +/// the serial of the pane the walk landed on. +/// The open is what makes the pane; the handle it answers is the serial, which +/// is also what a read of that fid reports. pub fn newPane(p: *Pardes) !u32 { - const made = mkdir(p, "scratch"); - if (made.reply.status != .ok) return error.NoPane; - const target = tree.Node.target(made.reply.attr.node) orelse return error.NoPane; - return switch (target) { - .pane => |t| t.serial, - .top => error.NoPane, - }; -} - -pub fn mkdir(p: *Pardes, name: []const u8) Answer { - return call(p, .{ - .tag = 9, - .op = .open, - .node = @intFromEnum(tree.TopFile.pane), - .data = name, - .create = true, - .perm = 0x8000_0000 | 0o755, - }); + const made = call(p, .{ .tag = 8, .op = .open, .node = @intFromEnum(tree.TopFile.new) }); + if (made.reply.status != .ok or made.reply.handle == 0) return error.NoPane; + return made.reply.handle; } pub fn rmdir(p: *Pardes, node: u64) Answer { -- cgit v1.3