1 files changed, 29 insertions, 4 deletions

diff --git a/src/ninep/tree.zig b/src/ninep/tree.zig
index f98429ab..a85a1873 100644
--- a/src/ninep/tree.zig
+++ b/src/ninep/tree.zig
@@ -61,6 +61,20 @@ pub fn failText(tag: u64, errno: u16, text: []const u8) Reply {
 pub const e_bad_addr = "bad address syntax";
 pub const e_bad_ctl = "ill-formed control message";
 pub const e_bad_event = "bad event syntax";
+/// A second open reading a file whose reads consume: rio's word for it
+/// (windows/rio/xfid.c:25), which 9ns turns into EBUSY.
+pub const e_in_use = "file in use";
+
+/// Handles that mark an open as the one reading `event` or `pty/data`, so the
+/// release knows to give the file up; other opens get `open_handle`.
+const open_handle: u32 = 1;
+// ponytail: EBUSY spelled locally; use E.BUSY once cloud9 names it and pardes bumps the pin.
+const e_busy: u16 = 16;
+const reader_handle: u32 = 2;
+
+fn reads(omode: u8) bool {
+    return omode & 3 != 1; // OWRITE is the one access mode that never reads
+}
 
 /// Tremove closes a pane; nothing else in the tree is created or destroyed by
 /// the protocol, and wstat stays a truncation. Making a pane is an open of
@@ -167,7 +181,7 @@ pub const PaneFile = enum(u5) {
     pub fn mode(f: PaneFile) u16 {
         return switch (f) {
             .dir, .pty => 0o755,
-            .errors, .pty_ctl => 0o222,
+            .errors => 0o222,
             .pty_status => 0o444,
             else => 0o666,
         };
@@ -507,16 +521,26 @@ fn open(p: *Pardes, req: Req, target: Target) Reply {
             if (t.file.inPty() and !pn.isTerminal()) return Reply.fail(req.tag, E.NOENT);
             switch (t.file) {
                 .body => if (pn.isTerminal()) return screen.openSnapshot(p, req, false),
+                // Reads of these consume, so two readers would each see half
+                // the stream; the second is refused rather than robbed.
                 .event => {
+                    const reader = reads(req.omode);
+                    if (reader and pf.event_reader) return failText(req.tag, e_busy, e_in_use);
                     pf.readers +|= 1;
                     p.fs.listeners +|= 1;
+                    pf.event_reader = pf.event_reader or reader;
+                    if (reader) return .{ .tag = req.tag, .handle = reader_handle };
+                },
+                .pty_data => if (reads(req.omode)) {
+                    if (pf.pty_readers > 0) return failText(req.tag, e_busy, e_in_use);
+                    pf.pty_readers = 1;
+                    return .{ .tag = req.tag, .handle = reader_handle };
                 },
-                .pty_data => pf.pty_readers +|= 1,
                 else => {},
             }
         },
     }
-    return .{ .tag = req.tag, .handle = 1 };
+    return .{ .tag = req.tag, .handle = open_handle };
 }
 
 /// Tremove closes a pane. Nothing else in the tree can be removed, and this
@@ -549,12 +573,13 @@ fn releaseHandle(p: *Pardes, req: Req) Reply {
             const id = p.paneBySerial(t.serial) orelse return .{ .tag = req.tag };
             const pf = &p.fs.panes[id];
             if (t.file == .pty_data) {
-                if (pf.pty_readers == 0) return .{ .tag = req.tag };
+                if (req.handle != reader_handle or pf.pty_readers == 0) return .{ .tag = req.tag };
                 pf.pty_readers -= 1;
                 if (pf.pty_readers == 0) pf.pty_out.clearAndFree(p.gpa);
                 return .{ .tag = req.tag };
             }
             if (pf.readers == 0) return .{ .tag = req.tag };
+            if (req.handle == reader_handle) pf.event_reader = false;
             pf.readers -= 1;
             p.fs.listeners -|= 1;
             if (pf.readers == 0) pf.tag_snap.clearAndFree(p.gpa);