cloud9 re-pinned at e66b2cf, whose 9ns opens files with FOPEN_PARALLEL_DIRECT_WRITES: an Edit filter writing, through a mount, the ctl its Edit came by (without truncating it) answers at once, not after 10 s; selfmount checks it

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 11 insertions, 0 deletions

diff --git a/test/selfmount.py b/test/selfmount.py
index 347093e1..c6565b5e 100644
--- a/test/selfmount.py
+++ b/test/selfmount.py
@@ -256,6 +256,17 @@ def run(binary):
                 time.sleep(.05)
             check(got == '0' and all(f' held-{i}\n' in log for i in range(1, 41)),
                   f'40 closes holding a last line each through the mount, all answered, every line run ({got!r})')
+            # An Edit whose filter writes the very ctl the Edit came by: 9ns
+            # opens with FOPEN_PARALLEL_DIRECT_WRITES, so the filter's write
+            # is not queued behind the one waiting for it. (Its own open may
+            # not truncate, `1<>`, not `>`: Linux takes the file's lock
+            # outright for an O_TRUNC open, and the waiting write holds it
+            # shared; nothing a server answers can change that.)
+            started = time.monotonic()
+            got = run(f"printf 'Edit ,>echo Msg filter-hi 1<> {mount}/pane/{scratch}/ctl\\n' > {mount}/pane/{scratch}/ctl\n".encode())
+            took = time.monotonic() - started
+            check(got == '0' and took < 5 and 'filter-hi' in client.read('/log').decode(),
+                  f'an Edit filter writing its own ctl through the mount answers promptly ({got!r}, {took:.1f}s)')
             # Forty event reads held through the mount, a follower each, and
             # the mount still answers the rest: 9ns keeps workers past what
             # the editor holds (128), so `cat layout` is not queued behind